WO2010107784A1

WO2010107784A1 - Methods for activation control of photopolymerization for holographic data storage using at least two wavelengths

Info

Publication number: WO2010107784A1
Application number: PCT/US2010/027466
Authority: WO
Inventors: Eric S. Kolb; David A. Waldman; Richard A. Minns
Original assignee: STX Aprilis Inc
Current assignee: STX Aprilis Inc
Priority date: 2009-03-16
Filing date: 2010-03-16
Publication date: 2010-09-23
Anticipated expiration: 2011-09-16

Abstract

A polymerizable media includes a holographic recording media. The media includes at least one monomer or oligomer that undergoes polymerization; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength.

Description

METHODS FOR ACTIVATION CONTROL OF

PHOTOPOLYMERIZATION FOR HOLOGRAPHIC DATA

STORAGE USING AT LEAST TWO WAVELENGTHS

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application

No. 61/210,230 filed on March 16, 2009, which is incorporated herein by reference, for any and all purposes.

BACKGROUND

[0002] As the need for increased data storage changes, the search for higher density and faster access for data storage technologies also increases. One of these, holographic data storage, provides the promise for fast access times , fast data transfer rates, and higher data density for optical storage. In holographic data storage, information is recorded as an ensemble of interference fringe patterns formed by the intersection of two coherent energy sources in the volume of the recording material. Typically, coherent light beams from lasers are utilized to perform the addressing, namely writing and reading of the data to and from the storage media by directing these beams at a specific region on the surface of the media. Interference fringes are then formed within a holographic recording media (HRM) including a homogeneous mixture of monomer or oligomer and a binder and a polymerization initiator. In the holographic media, this initiation, followed by polymerization, occurs in the light areas of the interference fringe pattern. In this process, monomer or oligomer diffuses into the light areas of the fringe structure to be incorporated into the growing polymer chains. Polymerization induced chemical segregation, in the case of a diffusible binder, drives the binder into the dark regions of the fringe structure. Since the monomer or oligomer and the binder have differing index of refraction an index modulation is achieved during the exposure process, thereby forming the hologram. [0003] The recording media is made sensitive to actinic radiation of a desired energy level (wavelength) by the incorporation of a photo initiator. The photo initiator may absorb light energy directly or may be sensitized to a desired wavelength or energy of irradiation by incorporation of a sensitizing dye. The normal polymerization procedure is to irradiate the photopolymerizable material with photons having energy that initiates the polymerization process. The reaction sequence associated with this process is complex. A simplified, but reasonably good model is as follows: the sensitizing dye compound is first exited by a photon of proper energy, and then the excited dye transfers energy to the initiator, photo acid generator, (PAG), for example, to provide an activated initiator species, or the excited state dye reacts with the initiator via a oxidation-reduction process to form an initiative species. In either case, the initiative species, or activated initiator, then combines with or actives a monomer, which begins a chain reaction with additional monomers to result in polymerization.

[0004] The sensitizer dyes that are typically used are linear absorbers at the exposure wavelengths for recordation. These sensitizer dyes work by converting light energy into chemical initiative species at some quantum efficiency associated with the molecular make-up of the dye molecule and its chemical surroundings. The use of said dye in conjunction with, by example, a PAG leads to holographic media with high recording sensitivity as well as other favorable characteristics, such as bleaching. The utilization of a linear absorber yields a holographic or photo-polymerizable medium with a linear response to the exposure energy of actinic radiation. In such a system, the initiation of polymerization, the strength of the hologram formed and the amount of monomer or oligomer polymerized after a particular photo-initiated event is proportional to the amount of actinic radiation or exposure fluence the media has been received in a location or storage volume.

[0005] One problem with the utilization of linear absorbers in a holographic media for data storage is evident when angle multiplexing volume holograms, particularly in thick media. Holograms are recorded in a photopolymer medium with a finite angle between the reference beam and the signal beam, this angle is generally referred to as the inter beam angle. Many volume holograms can be recorded in the same volume location, such as by changing the inter beam angle for each recording or by changing the angle of incidence of either beam with respect to the volume location in the medium so as to change the angle by an amount that satisfies the Bragg selectivity criteria. Each angle combination between the signal beam and the reference beam represents a unique volume hologram. The process of recording a grouping of volume holograms in the same volume element is referred to co- locational multiplexing. The larger the dynamic range, the greater the number of holograms that can be recorded in the particular location, and thus a larger data storage density. Typically the dynamic range in a photopolymer medium is proportional to the amount of active monomer and or oligomer available for polymerization and the magnitude of the difference in the index of refraction between the monomer and the binder that chemically segregate during the recording process. In one method of recording, after fully consuming the dynamic range in a particular location, hologram recording can commence in a grouping of new locations until all the dynamic range in the media is fully consumed. Ideally, each storage location is arranged in a closest-packed geometry to optimally use the media's dynamic range and thus maximize the storage density. The recordation of holograms, however, only takes place in the beam overlap region in the hologram recording material (i.e. in the volume of the interference pattern of the recording beams). Outside the region of the interference pattern, where the reference and signal beam impinge on, or in, the recording material but do not overlap, photopolymerization is initiated at a rate, or amount, associated with the photon flux and the quantum efficiency of initiation. This unintended polymerization consumes photoinitiator as well as monomers/oligomers, thus wasting the dynamic range in the volume element surrounding a particular storage location. This unintended polymerization has a significant impact on the overall storage density achievable in a holographic media and is exacerbated as the thickness of the recording material increases.

[0006] One proposed solution to this problem is to include an inhibitor in the recording medium. The inhibitor prevents premature polymerization and keeps the media in an inactive state by consuming or quenching initiating species as they are formed, either by reacting with the photoinitiator or by reacting/quenching growing polymer chain ends, thereby limiting or preventing polymerization and preventing formation of holograms. In order to form holograms, the inhibitor needs to be removed or otherwise chemically reacted or depleted. After the inhibitor is depleted in a region then the initiator can then react with monomer(s) to effect polymerization and record holograms. Once the threshold exposure is achieved, depleting an inhibitor in the storage location, the hologram recording process can initiate. In such a system, especially for thick media, exposure outside the overlap region of the recording beams is significant and will lead to premature consumption of inhibitor. Without sophisticated tracking of the amount of exposure in the regions outside the overlap regions it will remain difficult to properly track the amount of inhibitor in regions abutting a storage location, and the degree of exposure to deplete inhibitor will fluctuate during the exposure process. Additionally, as an inhibitor is depleted, so too is the initiator used to initiate polymerization for hologram recording. This will reduce the amount of photoinitiator available for hologram recording and in turn reduce the recording sensitivity, and, further, will cause fluctuation in the amount of photoinitiator.

[0007] One approach to achieve high storage density is to use a non-linear absorber as the photosensitizer in the photopolymerizable medium. In such a system a two-photon process, or multi-photon process, is used to create a localized region for polymerization. The polymerization region is localized due to the non-linear absorption properties of the two-photon dye, where the absorption probability depends quadratically on light intensity. Thus a two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution. Unfortunately, the non- linear nature of the absorption makes the use of a two-photon absorber unsuitable for display holography or for data page recoding, where the hologram is recorded uniformly throughout the storage volume, and, further, the nonlinear nature equates to low quantum efficiency and thus low recording sensitivity. SUMMARY

[0008] The present invention relates to a polymerizable media in which a sensitizer is produced in situ as well as to the methods of use of such a polymerizable media.

[0009] In one aspect, a polymerizable media is provided, including at least one monomer or oligomer which undergoes polymerization to form a polymer; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength.

[0010] In another aspect, a method of polymerizing a polymerizable media is provided. The polymerizable media includes at least one monomer or oligomer which undergoes polymerization to form a polymer; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength. The method includes (a) exposing a first location in the polymerizable media to actinic radiation of the first wavelength, thereby forming the sensitizer from the compound; and (b) exposing the first location in the polymerizable media to actinic radiation of the second wavelength, thereby initiating polymerization of the at least one monomer or oligomer.

[0011] In another aspect, a method of recording a hologram in a HRM is provided. The HRM includes at least one monomer or oligomer which undergoes polymerization; a binder; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer initiates polymerization of the at least one monomer or oligomer, when said sensitizer is exposed to actinic radiation of the second wavelength. The method includes (a) exposing a first storage location in the HRM to a beam of actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing actinic radiation of a second wavelength; and (b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer in the volume of the said interference pattern and thereby recording the interference pattern as a hologram within said first storage location.

[0012] In another aspect, a method of recording a micrograting hologram in a

HRM is provided, which includes at least one monomer or oligomer which undergoes polymerization; a binder; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer initiates polymerization of the at least one monomer or oligomer, when said sensitizer is exposed to actinic radiation of the second wavelength. The method includes (a) exposing a first storage location in the HRM to actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing electromagnetic radiation of a second wavelength, said first storage location being located in a portion of the depth of the HRM; and (b) directing a reference beam of the second wavelength and an object beam of the second wavelength at the first storage location, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, and initiating polymerization of the at least one monomer or oligomer in the volume of the interference pattern in the first storage location and thereby recording the interference pattern as a hologram within said first storage location. As used herein, the phrase "a portion of the depth of the HRM" means a fraction of the thickness of the HRM, usually corresponding to Rayleigh length(s). The fraction can be any number between 0 and 1, e.g. 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the thickness. Further, the reference or signal beam can optionally be created by reflection of the signal or reference beam, respectively.

[0013] In another aspect, a method of recording a hologram, in a HRM is provided. The HRM includes at least one monomer or oligomer which undergoes polymerization; a binder; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer initiates polymerization of the at least one monomer or oligomer, when said sensitizer is exposed to actinic radiation of the second wavelength. The method includes (a) exposing a first storage location in the HRM to a beam of actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing electromagnetic radiation of a second wavelength; and (b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location in the HRM, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer and recording the interference pattern therefrom as a hologram within said first storage location. In some embodiments, the beam of actinic radiation of the first wavelength, and the reference and object beams, is each independently generated, such as by a tunable light source. The sensitizer is formed in the volume of the exposure of the first storage location in the HRM, therefore the region of overlap between the reference beam and object beam of the second wavelength that occurs in the volume comprising the sensitizer formed by the exposure of the first storage location in the HRM to the first wavelength corresponds to the volume in the HRM where the interference pattern is recorded as a hologram.

[0014] In another aspect, an optical article is provided. The optical article includes one, or two or more substrates; and a HRM thereon or therebetween. The HRM includes at least one monomer or oligomer which undergoes polymerization; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength.

[0015] In another aspect, a media for holographic recording is provided that exhibits a controlled threshold for a recording event. Consequently, multiple recordings (e.g., multiplexed holograms) can be made in a given volume of the polymerizable media without loss of dynamic range due to depletion of photoreactive media components or undesirable light absorption on the sensitizer dye molecules.

[0016] The polymerizable media and the disclosed methods provide for substantial increase in the storage density, as illustrated in FIG. 5.

In some embodiments, the polymerizable media and disclosed methods allow for the recording of one or more holograms at a sensitized active location in a HRM while substantially no preconsumption of dynamic range of the HRM (e.g. due to spillover of the holographic recording beams) occurs at unsensitized inactive locations in the HRM. This feature is an improvement over certain prior sensitizable HRM, in which preconsumption of dynamic range was reduced but not substantially eliminated at inactive locations in the HRM.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.

[0018] FIG. 1 is a schematic diagram showing an exemplary optical architecture for recording Fourier transform volume holograms, according to various embodiments.

[0019] FIG. 2 is a schematic diagram showing a portion of the HRM at the area of impact of the object and reference beams, according to various embodiments. [0020] FIG. 3(A) is a schematic representation of one embodiment of the optical geometry of reference beam and the object beam, according to various embodiments.

[0021] FIG. 3(B) illustrates a detail of FIG. 3(A) at the area where the reference and object beams are incident onto the HRM, according to various embodiments.

[0022] FIG. 4 is a schematic representation a selected storage location in a

HRM in cross section view being illuminating with actinic radiation at a first wavelength 1' that activates the storage location in the HRM for recording holograms, according to various embodiments.

[0023] FIG. 5 is a plot the storage density in bits/μm² as a function of thickness of the recording material in μm, according to various embodiments.

[0024] FIG. 6 is a plot showing diffraction efficiency, η, of multiplexed holograms as a function of recording exposure energy E, according to various embodiments.

[0025] FIGs. 7A and 7B are ¹HNMR spectra for compound S7-closed.

[0026] FIG. 8 is a ¹HNMR spectra for compound S8a.

[0027] FIG. 9 is a graph of the Photo Differential Scanning Calorimetry

(PDSC) results for 5,5"-Dimethyl-2,2':5',2"-terthiophene (DMTT) sensitized photopolymerization with 407 nm light, according to one example.

[0028] FIG. 10 is a comparative graph of the PDSC results for open and closed compound S7, according to the examples.

[0029] FIG. 11 is a graph showing the growth in cumulative grating strength versus the cumulative recording fluence in mJ/cm for the nine co-locationally multiplexed planar angle volume holograms recorded in the material at the second wavelength (λ₂) immediately after the in situ activation was carried out at the first wavelength (X₁) and after a wait time of 17 hours after the same activation step before recording at the second wavelength (λ₂), according to the examples.

[0030] FIG. 12 is a graph showing the recording sensitivity versus the cumulative recording fluence in mJ/cm² for the nine co-locationally multiplexed planar angle volume holograms recorded in the material at the second wavelength (λ₂) immediately after the in situ activation was carried out at the first wavelength (X₁) and after a wait time of 17 hours after the same activation step before recording at the second wavelength (λ₂), according to the examples.

DETAILED DESCRIPTION

Glossary

[0031] As used herein, the term "actinic radiation" refers to any electromagnetic radiation capable of initiating photochemical reactions. It includes microwave, IR, VIS and UV wavebands.

[0032] As used herein, the term "conjugation" refers to a set of contiguous and covalently bonded atoms where each atom posses a p-orbital and the molecular arrangement results in a derealization of electrons across adjacent parallel aligned or substantially parallel aligned p-orbitals. A conjugated sequence typically includes a sequence of alternating single and double bonds, (e.g., -C=C-C=C-) or single and triple bonds, (e.g.,-C≡C-C≡) or a combination of alternating single and double and single and triple bonds (e.g. -C=C-C=C), wherein the sequence can be acyclic or cyclic and can comprise a hetero atom such a O, S, N atom as long as derealization is maintained.

[0033] As used herein the term "delocalized" refers to orbital character where the electrons are distributed or shared along a contiguous sequence of atoms.

[0034] As used herein, an "alkyl group", alone or as a part of a larger moiety

(alkoxy, alkylammonium, and the like) is preferably a straight chain or branched saturated aliphatic group with 1 to about 12 carbon atoms, e.g., methyl, ethyl, n- propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl or octyl, or a saturated cycloaliphatic group with 3 to about 12 carbon atoms.

[0035] The term "cycloalkyl", as used herein, means saturated cyclic hydrocarbons, i.e. compounds where all ring atoms are carbons. Examples of cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl.

[0036] The term "haloalkyl", as used herein, includes an alkyl substituted with one or more F, Cl, Br, or I, wherein alkyl is defined above.

[0037] The terms "alkoxy", as used herein, means an "alkyl-O-" group, wherein alkyl is defined above. Examples of alkoxy group include methoxy or ethoxy or propoxy or butoxy groups and may be branched.

[0038] As used herein, an "alkenyl group", alone or as a part of a larger moiety (e.g., cycloalkene oxide), is preferably a straight chain or branched aliphatic group having one or more double bonds with 2 to about 12 carbon atoms, e.g., ethenyl, 1-propenyl, 1-butenyl, 2-butenyl, 2-methyl-l-propenyl, pentenyl, hexenyl, heptenyl or octenyl, or a cycloaliphatic group having one or more double bonds with 3 to about 12 carbon atoms.

[0039] As used herein, an alkynyl group, alone or as a part of a larger moiety, is preferably a straight chain or branched aliphatic group having one or more triple bonds with 2 to about 12 carbon atoms, e.g., ethynyl, 1-propynyl, 1-butynyl, 3- methyl-1-butynyl, 3, 3 -dimethyl- 1-butynyl, pentynyl, hexynyl, heptynyl or octynyl, or a cycloaliphatic group having one or more triple bonds with 3 to about 12 carbon atoms.

[0040] As used herein, an "aryl", alone or as part of a larger moiety (e.g. diaryl ammonium) is a carbocyclic aromatic group, preferably including 6-22 carbon atoms. Suitable aryl groups for the present invention are those which 1) do not react directly with light in the absence of an initiator to initiate or induce polymerization of any type, and 2) do not interfere with polymerization. Examples include, but are not limited to, carbocyclic groups such as phenyl, naphthyl, biphenyl, anthracenyl, and phenanthryl.

[0041] The term "heteroaryl", as used herein, alone or as a part of a larger group, refers to aromatic groups containing one or more heteroatoms (O, S, or N). A heteroaryl group can be monocyclic or polycyclic, e.g. a monocyclic heteroaryl ring fused to one or more carbocyclic aromatic groups or other monocyclic heteroaryl groups. The heteroaryl groups of this invention can also include ring systems substituted with one or more oxo moieties. Examples of heteroaryl groups include, but are not limited to, pyridinyl, pyridazinyl, imidazolyl, pyrimidinyl, pyrazolyl, triazolyl, pyrazinyl, quinolyl, isoquinolyl, tetrazolyl, furyl, thienyl, isoxazolyl, thiazolyl, oxazolyl, isothiazolyl, pyrrolyl, quinolinyl, isoquinolinyl, indolyl, benzimidazolyl, benzofuranyl, cinnolinyl, indazolyl, indolizinyl, phthalazinyl, pyridazinyl, triazinyl, isoindolyl, purinyl, oxadiazolyl, thiazolyl, thiadiazolyl, furazanyl, benzofurazanyl, benzothiophenyl, benzotriazolyl, benzothiazolyl, benzoxazolyl, quinazolinyl, quinoxalinyl, naphthyridinyl, dihydroquinolyl, tetrahydroquinolyl, dihydroisoquinolyl, tetrahydroisoquinolyl, benzofuryl, furopyridinyl, pyrolopyrimidinyl, and azaindolyl.

[0042] The foregoing heteroaryl groups may be C-attached or N-attached

(where such is possible). For instance, a group derived from pyrrole may be pyrrol- 1- yl (N-attached) or pyrrol-3-yl (C-attached).

[0043] Suitable substituents on alkyl, alkoxy, alkenyl, alkynyl, aryl, and heteroaryl groups are those which 1) do not react directly with light in the absence of an initiator to initiate or induce polymerization of any type and 2) do not interfere with polymerization. Examples of suitable substituents include, but are not limited to Cl -C 12 alkyl, C6-C14 aryl, -OH, halogen (-Br, -Cl, -I and -F), -O(R'), -O-CO-(R'), - COOH, -N(R')₂, -COO(R'), -S(R') and -Si(R'₃). Each R' is -H or independently a substituted or unsubstituted aliphatic group or a substituted or unsubstituted aryl group. In one embodiment, R' is an unsubstituted alkyl group or an unsubstituted aryl group. Preferably, R' is a C1-C12 alkyl, C1-C12 halogenated alkyl, C3-C10 cycloalkyl; in other embodiments, more preferably R' is methyl, ethyl, 2-ethylhexyl, cyclohexyl, benzyl or a phenyl group. In another embodiment, R' is a phenyl substituted with one or more substituent groups such as Cl -C 12 alkyl, Cl -C 12 halogenated alkyl, C3-C10 cycloalkyl, halogen, phenyl or benzyl, or C1-C12 alkoxy, optionally substituted with C1-C12 alkyl or C1-C6 haloalkyl or C3-C10 cycloalkyl. More preferably, the substituents on phenyl are methyl, ethyl, 2-ethylhexyl, Cl -C 12 fluorinated or perfluorinated alkyl, cyclohexyl, benzyl, phenyl, 2-ethylhexyloxy, - OCH₃, chloro, or trifluoromethyl. In some embodiments, alkyl, alkoxy, alkenyl, alkynyl, aryl, and heteroaryl groups can optionally be substituted with one or more halogen, hydroxyl, Cl -C 12 alkyl, C2-C12 alkenyl or C2-C12 alkynyl group, Cl -C 12 alkoxy, or Cl -C 12 haloalkyl.

[0044] Further examples of suitable substituents for a substitutable carbon atom in alkyl, alkoxy, alkenyl, alkynyl, aryl, and heteroaryl groups include but are not limited to -OH, halogen (-F, -Cl, -Br, and -I), -R, -OR, -CH₂R, -CH₂OR, -CH₂CH₂OR. Each R is independently an alkyl group. In addition, alkyl, alkenyl, alkynyl, cycloalkyl, alkyl ene, a heterocyclyl, and any saturated portion of alkenyl, cycloalkenyl, alkynyl, arylalkyl, and heteroaralkyl groups, may also be substituted with =0, =S, =N-R.

[0045] In some embodiments, a C6-C14 aryl is a phenyl, indenyl, naphthyl, azulenyl, heptalenyl, biphenyl, indacenyl, acenaphthylenyl, fluorenyl, phenalenyl, phenanthrenyl, anthracenyl, cyclopentacyclooctenyl or benzocyclooctenyl.

[0046] In other embodiments, a 5-14-membered heteroaryl group is a pyridyl,

1-oxo-pyridyl, furanyl, benzo[l,3]dioxolyl, benzo[l,4]dioxinyl, thienyl, pyrrolyl, oxazolyl, imidazolyl, thiazolyl, a isoxazolyl, quinolinyl, pyrazolyl, isothiazolyl, pyridazinyl, pyrimidinyl, pyrazinyl, a triazinyl, triazolyl, thiadiazolyl, isoquinolinyl, indazolyl, benzoxazolyl, benzofuryl, indolizinyl, imidazopyridyl, tetrazolyl, benzimidazolyl, benzothiazolyl, benzothiadiazolyl, benzoxadiazolyl, indolyl, tetrahydroindolyl, azaindolyl, imidazopyridyl, quinazolinyl, purinyl, pyrrolo[2,3]pyrimidinyl, pyrazolo[3,4]pyrimidinyl, imidazo[l,2-a]pyridyl, and benzothienyl. [0047] In some embodiments, a C6-C14 aryl is a phenyl, naphthalene, anthracene, lH-phenalene, tetracene, or pentacene. In other embodiments, a C6-C14 aryl is an indenyl, azulenyl, heptalenyl, biphenyl, indacenyl, acenaphthylenyl, fluorenyl, phenalenyl, phenanthrenyl, cyclopentacyclooctenyl or benzocyclooctenyl. In some embodiments, a C6-C14 aryl is a phenyl, naphthalene, anthracene, tetracene, or pentacene.

[0048] In some embodiments, a 5-14-membered heteroaryl group is a pyridyl, furanyl, thienyl, pyrrolyl, imidazolyl, quinolinyl, pyrazolyl, indolyl, purinyl, or benzothienyl. In other embodiments, a 5-14-membered heteroaryl group is a 1-oxo- pyridyl, benzo[l,3]dioxolyl, benzo[l,4]dioxinyl, isoxazolyl, isothiazolyl, isoquinolinyl, benzofuryl, imidazopyridyl, pyrrolo[2,3]pyrimidinyl, pyrazolo[3,4]pyrimidinyl, or imidazo[l,2-a]pyridyl. In some embodiments, a 5-14- membered heteroaryl group is a pyridyl, furanyl, thienyl, pyrrolyl, imidazolyl, pyrazolyl, indolyl, and benzothienyl.

[0049] In some embodiments, any of the above C6-C14 aryl and/or 5-14- membered heteroaryl are optionally substituted. The substituents are selected from one or more of C1-C12 alkyl, C6-C14 aryl, -OH, halogen, -O(R'), -O-CO-(R'), - COOH, -N(R')₂, -COO(R'), -S(R') and -Si(R'₃). Preferably, the substituents are one or more of C1-C12 alkyl, -OH, halogen (preferably F, Cl, Br, or I), -O(R'), -O-CO- (R'), -N(R')₂, -COO(R'), and -Si(R'₃). More preferably, the substituents are one or more of C1-C12 alkyl, -OH, -F, -O(C1-C12 alkyl), amine, -N(R')₂, and -Si(R'₃).

[0050] R' can be any of the above C6-C14 aryl or 5-14-membered heteroaryl groups, or a C1-C12 alkyl, C1-C12 halogenated alkyl, C3-C10 cycloalkyl. Preferably, R' is a C1-C12 alkyl, C1-C12 halogenated alkyl, C3-C10 cycloalkyl; more preferably, R' is -H, methyl, ethyl, 2-ethylhexyl, cyclohexyl, benzyl or a phenyl group.

Polymerizable Media

[0051] As used herein, a "binder" refers to a compound or composition used in the polymerizable media which is chosen such that it does not inhibit polymerization of the monomers used, such that it is miscible with the monomers used as well as the polymerized or copolymerized structure, and such that its refractive index is significantly different from that of the polymerized monomer or oligomer. In some embodiments, the refractive index of the binder differs from the refractive index of the polymerized monomer by at least 0.04. In other embodiments, the refractive index of the binder differs from the refractive index of the polymerized monomer by at least 0.09. In some embodiments, the refractive index of the binder differs from the refractive index of the polymerized monomer 0.04 to 0.20. According to various embodiments, a binder is inert to the polymerization processes of the one or more polymerizable monomer(s). In some embodiments, the binder is diffusible. As used herein, the term diffusable refers to a material that may migrate or reorganize in a polymerizable media, as the polymerization of the media progresses. Diffusion of the monomer(s) and/or oligomer(s) into the illuminated regions during polymerization reactions, with consequent chemical segregation of binder from these areas and alteration in its concentration in the illuminated and non-illuminated regions, produces spatial separation between the polymer formed from the monomer(s) and/or oligomer(s) and the binder thereby providing the refractive index modulation needed to form a hologram. Diffusible binders can, by way of example, segregate from the polymerizing monomer(s) or oligomer(s) during holographic recording via diffusion-type motion of the binder component. Examples of binders for use in HRM are polysiloxanes, due in part to availability of a wide variety of polysiloxanes and the well documented properties of these oligomers and polymers. The physical, optical, and chemical properties of the polysiloxane binder can all be adjusted for optimum performance in the recording medium inclusive of, for example, dynamic range, recording sensitivity, image fidelity, level of light scattering, and data lifetime. The efficiency of holograms produced by the present process in the present medium is markedly dependent upon the particular binder employed. Commonly used binders include poly(methyl phenyl siloxanes) and oligomers thereof, 1,3,5- trimethyl-l,l,3,5,5-pentaphenyltrisiloxane and other pentaphenyltrimethyl siloxanes, or cyclic siloxanes that may be optionally substituted with Cl -C 12 alkyl or optionally substituted C3-C12 cycloalkyl or an optionally substituted aryl or an optionally substituted heteroaryl. Examples are sold by Dow Corning Corporation under the trade name Dow Corning 710, Dow Corning 705, and oligio (poly)phenylethers sold as Convalex Oils have been found to give efficient holograms. More preferable binders comprise a star of a multi-armed (at least 3 arms) siloxane core, wherein the terminus of each arm is a high refractive index moiety (see for example Structural Formula (I) in PCT publication WO 2007/047840 A3. The refractive index of the terminus of each arm should be at least 1.545, more preferably 1.565, still more preferably 1.585. As used herein, the term "multiarmed siloxane core terminated with high refractive index moieties" refers to a composition of matter having the refractive index of at least 1.550, preferably at least 1.600. In a preferred embodiment, refractive index of any one moiety attached as the terminus of an arm to the siloxane core should preferably be at least about 1.545, more preferably at least 1.565, still more preferably at least 1.585. Other binders can comprise a cyclic methyl-siloxane core with pendent aromatic moieties, as shown in Structural Formula (II) in WO 2007/047840 A3, wherein n is the number of methylsiloxane units in the cyclic structure. The cyclic siloxane core comprises at least 3 substituted methylsiloxane units. The cyclic siloxane core is preferably composed of at least 4 repeat units and more preferably the siloxane core comprises a mixture of ring sizes from n = 3 to about n=6 repeat units.

[0052] In one embodiment, the polymerizable media includes a compound that undergoes a molecular rearrangement reaction upon exposure to actinic radiation of the first wavelength to form the sensitizer which absorbs actinic radiation of the second wavelength. An example of such a rearrangement is a 6π electrocyclic cyclization upon exposure to actinic radiation of the first wavelength.

[0053] In some embodiments, the compound that undergoes a molecular rearrangement is a spiropyran, spiro-oxazine, fulgide (dialkylidenesuccinic anhydride), triarylmethane, naphthopyran, diarylethene or diheteroarylethene. In some embodiments, the compound is a diarylethene or a diheteroarylethene, where the aryl or heteroaryl moiety is a substituted or unsubstituted phenyl, a substituted or unsubstituted naphthyl, a substituted or unsubstituted thiophene, a substituted or unsubstituted benzathiophene, a substituted or unsubstituted pyrrole, and a substituted or unsubstituted indole. In some embodiments, the ethene moiety of the diarylethene and diheteroarylethene is optionally substituted and/or is a part of an optionally substituted cycloalkene, an optionally substituted anhydride, or optionally substituted maleimide. Where the ethene moiety is an optionally substituted cycloalkene, the cycloalkene moiety is a C4-C6, optionally perfluorinated, cycloalkene. In some embodiments, alkyl, alkenyl, aryl and heteroaryl groups and suitable substituents are as described above for the corresponding groups.

[0054] In some embodiments, the compound that undergoes a molecular rearrangement is represented by the following structural formula:

(V), and the sensitizer is represented by the following structural formula

(VI).

[0055] In the structural formulas V and VI, ring C is an optionally fluorinated or perfluorinated C3-C7 cycloalkenyl and ring C is an optionally fluorinated or perfluorinated C3-C7 cycloalkane; X₁ is a linker group that provides for conjugation between Ar₁ and the thienyl group with which X₁ is connected; X₂ is absent or is a linker group that provides for conjugation between Ar₂ and the thienyl group with which X₂ is connected; Ar₁ is an optionally substituted C6-C22 aryl or an optionally 5-14-membered heteroaryl; Ar₂ is independently an Ar₁, wherein the optical absorbance characteristics for the Ar₁ or Ar₂ moiety can be for a specific wavelength or range of wavelengths of actinic radiation. Alternatively, -X₂-Ar₂ is an electron donating group or an electron withdrawing group. R₃ and R₄ are each independently selected form a Cl-Cl 2 alkyl group, a Cl-Cl 2 alkenyl group, or a Cl-C 12 alkoxy group. Preferred alkyl, alkenyl, aryl and heteroaryl groups and suitable substituents are as defined above for the corresponding groups.

[0056] As used herein, the term " linker" or "linking group" refers to a moiety which: 1) does not react under conditions which induce or initiate polymerization; 2) does not interfere with polymerization; 3) does not interfere with chemical segregation of the binder from a polymer formed during polymerization; 4) and provides for conjugation between the groups linked together. Examples of linking groups include, but are not limited to, an alkenyl group, an alkynyl group, a carbonyl group, a grouping including a carbonyl, a sequence of alternating single and double bonds (e.g. ,-C=C-C=C-), a sequence of alternating single and triple bonds (e.g.,-C≡C- C≡), or a combination of alternating single and double and single and triple bonds (e.g. -C=C-C=C), wherein the sequence can be acyclic or cyclic and can comprise a hetero atom such a O, S, or N atom as long as derealization providing for conjugation is maintained. In some embodiments, X₁ and X₂ are the same. In other embodiments, X₁ and X₂ are not the same.

[0057] In some embodiments, in the compounds of Formula V or VI, Ar₁ for each occasion is independently optionally substituted with a group represented by R^y, where R^y is an optionally substituted Cl -C 12 alkyl, an optionally substituted C2-C12 alkenyl, an optionally substituted C2-C12 alkynyl, an optionally substituted C3-C12 cycloalkyl, an optionally substituted C3-C12 cycloalkenyl, an optionally substituted C6-C14 aryl, or an optionally substituted 5-14-membered heteroaryl or is an electron- donating group selected from Cl -C 12 alkoxy, Cl -C 14 dialkylamine, and a C6-C14 diarylamine, or is an electron-withdrawing group selected from -NO₂, -CF₃, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', and a halogen, wherein R' is -H or a Cl -C 12 alkyl.

[0058] In some embodiments, in the compounds of Formula V or VI, wherein each linker group is independently an ethynyl group or an ethenyl group; Ar₁ is an optionally substituted C6-C22 aryl; and Ar₂ is an optionally substituted C6-C22 aryl. Preferably, where each linker group is independently an ethynyl group or an ethenyl group; Ar₁ is substituted or unsubstituted phenyl, naphthyl, or anthracenyl; and Ar₂ is substituted or unsubstituted phenyl, naphthyl, or anthracenyl.

[0059] Preferably, in some embodiments, in the compounds of Formula V or

VI, Ar₁ and Ar₂ have the values as described in the previous paragraph and are independently unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3-C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14- membered heteroaryl, an optionally substituted Cl -C 12 alkoxy, Cl -C 14 dialkylamine, a C6-C14 diarylamine, -NO₂, -CF₃, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', or a halogen, and further wherein R' is -H or a Cl-Cl 2 alkyl. More preferably, Ar₁ and Ar₂ are independently unsubstituted or substituted with -Si(R₅)₃; C1-C12 alkyl group, optionally substituted with -Si(R₅)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; or a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; and wherein each Rs is independently a C1-C12 alkyl. Still more preferably, Ar₁ and Ar₂ are independently unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.

[0060] In some embodiments, in the compounds of Formula V or VI, each linker group is an ethynyl group; and Ar₁ and Ar₂ are anthracen-9-yl or 6- methoxynaphthalen-2-yl. In other embodiments, each linker group is thienyl.

[0061] In some embodiments, in the compounds of Formula V or VI, X₁ is phenyl or 5-6 membered heteroaryl and X₂ is absent, wherein the group represented by X₁ is optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl- C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano. In other embodiments, X₂ is absent and X₁ is thienyl optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl -C 12 haloalkoxy or cyano. Preferably, Ar₁ is optionally substituted phenyl or optionally substituted thienyl; and Ar₂ is optionally substituted phenyl. In other preferred embodiments, Ar₁ is optionally substituted thienyl.

[0062] For the compounds of Formula V or VI, X₁ and for the embodiments described in the previous paragraph is phenyl or 5-6 membered heteroaryl and X₂ is absent, Ar₁ and Ar₂ are independently unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3-C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14-membered heteroaryl, an optionally substituted C1-C12 alkoxy, Cl- C14 dialkylamine, a C6-C14 diarylamine, -NO₂, -CF3, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', or a halogen, and further wherein R' is -H or a Cl-Cl 2 alkyl. Preferably, Ar₁ and Ar₂ are independently unsubstituted or substituted with - Si(Rs)₃; C1-C12 alkyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; and wherein each R₅ is independently a Cl-C 12 alkyl. More preferably, Ar₁ and Ar₂ are independently unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl- C 12 haloalkoxy or cyano. In some embodiments, Ar₁ is optionally substituted with Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl and Cl -C 12 haloalkyl and the group represented by Ar₂ is optionally substituted with halogen, Cl -C 12 alkyl, Cl- C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl -C 12 haloalkoxy or cyano.

[0063] In some embodiments, in the compounds of Formula V or VI, -X₂-Ar₂ is an electron withdrawing group. Preferably, -X₂-Ar₂ is halogen, Cl -C 12 alkyl or

C1-C12 haloalkyl. In some such embodiments, X₁ is phenyl or 5-6 membered heteroaryl and wherein the group represented by X₁ is optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl- C 12 alkoxy, Cl -C 12 haloalkoxy or cyano. Preferably, X₁ is thienyl optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.

[0064] Also, for the embodiments described in the previous paragraph, Ar₁ is preferably optionally substituted phenyl or thienyl. In some such embodiments, -X₂-Ar₂ is as described in the previous sentences and Ar₁ is optionally substituted thienyl. In some embodiments, Ar₁ is unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3-C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14-membered heteroaryl, an optionally substituted C1-C12 alkoxy, Cl- C14 dialkylamine, a C6-C14 diarylamine, -NO₂, -CF₃, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', or a halogen, and further wherein R' is -H or a Cl -C 12 alkyl. In other embodiments, the group represented by Ar₁ is unsubstituted or substituted with -Si(Rs)₃; C1-C12 alkyl group, optionally substituted with -Si(R₅ )₃, a Cl -C 12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; or a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; and wherein each R₅ is independently a C1-C12 alkyl. Preferably, Ar₁ is unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano. More preferably, Ar₁ is optionally substituted with C1-C12 alkyl, C1-C12 alkenyl, Cl -C 12 haloalkenyl and Cl -C 12 haloalkyl and the group represented.

[0065] In some embodiments, in the compounds of Formula V or VI, Ar₁ is thienyl optionally substituted with F, Cl, Br, I, CN, Cl -C 12 alkyl, or haloalkyl. [0066] In some embodiments, in the compounds of Formula V or VI, Ar₁ is a hexylthienyl group, a phenyl group, a methoxyphenyl group, a naphthyl group, an anthracenyl group, a phenylanthracenyl group, a methoxyanthracenyl group, or methylthienyl group; and Ar₂ is a hexylthienyl group, a phenyl group, a methoxyphenyl group, a naphthyl group, an anthracenyl group, a phenylanthracenyl group, a methoxyanthracenyl group, methylthienyl group, a trifluoromethylphenyl group, a bis-trifluoromethylphenyl group, or Br.

[0067] For the embodiments in the ten previous paragraphs, ring C is preferably a perfluorocyclopentene and ring C is a perfluorocyclopentane.

[0068] Another embodiment of the invention is a compound of Formula V or

VI, or any one of the more specific embodiments thereof described herein.

[0069] Some examples of sensitizers described and depicted below are intended to be instructive and are by no means limiting as to the scope of the present invention:

[0070] Alternatively, the Sensitizer dye can be asymmetric wherein the substituents directly on the ethene moiety are not the same, e.g.,

[0071] In some embodiments, Ar₁, Ar₂, or Ar₃ can have optical absorbance characteristics at a specific wavelength or grouping of wavelengths of actinic radiation. In the compounds of Formula VII and VIII, Ar₁, Ar₂, or Ar₃ for each occasion is independently optionally substituted with a group represented by an optionally substituted Cl -C 12 alkyl, an optionally substituted C2-C12 alkenyl, an optionally substituted C2-C12 alkynyl, an optionally substituted C3-C12 cycloalkyl, an optionally substituted C3-C12 cycloalkenyl, an optionally substituted C6-C14 aryl, or an optionally substituted 5-14-membered heteroaryl or is an electron-donating group selected from Cl -C 12 alkoxy, Cl -C 14 dialkylamine, or a C6-C14 diarylamine. Preferably, the optional substituent for each occurrence, is independently selected from -Si(Rs)₃; C1-C12 alkyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl- C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine, and wherein each R₅ is independently a C1-C12 alkyl, a C6-C14 aryl, or a 5-14-membered heteroaryl group. Preferred alkyl, alkenyl, aryl and heteroaryl groups and suitable substituents are as described above for the corresponding groups. In the compound of Formula VII, X is a linker group that provides for conjugation between Ar₃ and the thienyl group with which X₁ is connected.

[0072] In one embodiment of the present invention, the formed sensitizer is a linear absorbing dye. Alternatively, the formed sensitizer is a non-linear-absorbing dye. In one embodiment, the formed sensitizer is a 2-photon absorbing dye.

[0073] According to some embodiments, the polymerizable media includes an initiator. The initiator can initiate any type of a polymerization reaction. In one embodiment, the initiator is a photoacid generator (PAG), wherein the PAG produces acid in combination with the sensitizer. Preferably, the PAG is a sulfonium, sulfoxonium, iodonium, diazonium, or phosphonium salt.

[0074] In some embodiments, at least one monomer or oligomer included into the polymerizable media undergoes cationic polymerization. Preferably, the monomer or oligomer which is capable of undergoing polymerization contains one or more epoxide, oxetane, cyclic ether, 1-alkenyl ether, unsaturated hydrocarbon, lactone, cyclic ester, lactam, cyclic carbonate, cyclic acetal, aldehyde, cyclic sulfide, cyclosiloxane, cyclotriphosphazene, or polyol functional groups, or a combination thereof. More preferably, the epoxide monomer is a siloxane or siloxysilane including two or more cyclohexene oxide groups, or a polyfunctional siloxane including three or more cyclohexene oxide groups. For example, the monomer is an epoxide monomer that includes one or more cyclohexene oxide groups. Further description of suitable siloxane monomers can be found in aforementioned U.S. Patent Nos. 6,784,300 and 7,070,886 and PCT Publication WO 02/19040.

[0075] Alternatively, the polymerizable media includes an initiator that is a free radical generator, and wherein the free radical generator produces free radicals in combination with the sensitizer. In such an embodiment, the polymerizable media includes at least one monomer or oligomer undergoes free radical polymerization. Preferably, the produced free radicals initiate free radical polymerization reactions. In some embodiments, the initiator is a photoacid generator (PAG), wherein the PAG produces acid in combination with the sensitizer. Preferably, the PAG is a sulfonium, sulfoxonium, iodonium, diazonium, or phosphonium salt. An example of a sensitizer that can be formed from a compound in such a polymerizable media is diphenylanthracene.

Methods of polymerization and recording holograms

[0076] In one aspect, a method of polymerizing a polymerizable media is provided. The method includes (a) exposing a first location in the polymerizable media to actinic radiation of the first wavelength, thereby forming a sensitizer from the compound in a volume in the first location; and (b) exposing the first location in the polymerizable media to actinic radiation of the second wavelength, thereby initiating polymerization of the at least one monomer or oligomer in volume in the said first location.

[0077] In another aspect, a method of recording a hologram is provided. The method includes steps (a) exposing a first storage location in the HRM to a beam actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing actinic radiation of a second wavelength; and (b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer and thereby recording the interference pattern as a hologram within said first storage location. The sensitizer is formed from the compound in the volume of the exposure of the first storage location in the HRM, therefore the region of overlap between the reference beam and object beam of the second wavelength that occurs in the said volume comprising the sensitizer formed by the exposure of the first storage location in the HRM to the first wavelength is the volume in the HRM where the interference pattern is recorded as a hologram.

[0078] A hologram can be a binary data page hologram. For example, the data page hologram can be recorded with an object beam that is amplitude modulated or phase modulated and a reference beam that, by way of example, is a collimated or spherical wavefront and can optionally be phase coded or phase modulated.

[0079] Alternatively, the hologram can be a micrograting recorded in a portion of a volume of the first storage location in the HRM such as a portion of the depth of the volume. The micrograting can be recorded in a portion of the volume in the thickness direction of the HRM at the first storage location or in portion of the volume in the lateral direction at the first storage location, or combinations thereof. One or more microgratings can be recorded in a portion of the volume of the first storage location by repeating step (b) at the first storage location, thereby recording multiplexed microgratings that overlap at least in part in the said portion of the volume of the first storage location. The multiplexed microgratings can be recorded with two or more different wavelengths or two or more different phases.

[0080] In either the method of polymerizing, or the method of recording holograms, steps (a) and (b) can be repeated, and for each repetition of step (a), step (b) is repeated one or more times. Steps (a) and (b) can occur substantially at the same time. Preferably, steps (a) and (b) are performed at a second location in the polymerizable media. The second location can be abutting or at least partially overlapping the first location in one or more directions. Alternatively, the second location is neither abutting or overlapping the first location.

[0081] In some embodiments, the beam of actinic radiation of the first wavelength, the reference beam or the object beam are produced by a source of actinic radiation that is a continuous emitting source or a pulsed source. Examples of the source of actinic radiation include a frequency doubled diode pumped solid state laser (DPSS) or diode laser, and further, wherein the diode laser optionally includes an external cavity that is optionally temperature controlled. In some embodiments, the beam of actinic radiation of the first wavelength, the reference beam, or the object beam is each independently generated by a tunable light source such as tunable laser. In other embodiments, the beam of actinic radiation of the first wavelength is a light emitting diode (LED).

[0082] In some embodiments, the beam of actinic radiation of the first wavelength is a collimated or a substantially collimated beam.

[0083] The beam of actinic radiation of the first wavelength, the reference beam or the object beam can each independently have a Gaussian intensity distribution at the first storage location. Alternatively, the beam of actinic radiation of the first wavelength, the reference beam or the object beam can each independently have a truncated Gaussian intensity distribution at the first location in the HRM, wherein the minimum diameter of the truncated Gaussian intensity distribution is less than or equal to the diameter of said beam,

measured at the 1/e intensity point.

[0084] In certain embodiments, exposing the first location to actinic radiation of the first wavelength, the reference beam or the object beam exposes a volume element of the HRM having a cross-sectional area that changes as a function of depth through the HRM. [0085] The amount of formed sensitizer can be controlled by the intensity of the actinic radiation of a first wavelength or by the duration of the exposure of the compound to the actinic radiation of a first wavelength or combinations thereof.

[0086] The actinic radiation of a first wavelength can be used as a source of light for generating a servo signal from the media.

[0087] In some embodiments, the method of polymerizing the media and the method of recording a hologram can further include a step (c) of reading the recorded hologram after recording the hologram at the first storage location, wherein the reading step confirms the recording of the hologram at the first storage location (i.e. direct read after write). Step (c) can further include reading the recorded micrograting hologram after recording the micrograting hologram at the first storage location, wherein the reading step confirms the recording of the micrograting hologram at the first storage location.

[0088] In some embodiments, the method of polymerizing the media and the method of recording a hologram can further include performing steps (a) and (b) at a second storage location in the HRM before steps (a) and (b) or step (b) are repeated at the first storage location in the HRM for recording multiplexed holograms at the first storage location. Steps (a) and (b) are repeated at the first storage location for recording multiplexed holograms at the first storage location, after performing steps (a) and (b) at the second storage location in the HRM. This embodiment can be useful for further homogenizing recording sensitivity, such as during recording along a track on a disk or card, where multiple passes along the track can occur during recording so as to record using steps (a) and (b) at each of the storage locations along the track before repeating step (a) or step (b) at each of the said locations along the track.

In various embodiments, the multiplexed holograms recorded in the HRM at the first storage location using two or more multiplexing methods. In some embodiments, the multiplexed holograms are multiplexed with at least one multiplexing method selected from planar angle multiplexing, shift-multiplexing including co-linear shift multiplexing, phase-multiplexing, phase encoded multiplexing, azimuthally multiplexing, out-of-plane tilt-multiplexing, and polytopic spatial multiplexing.

[0089] It is desirable for a media for holographic recording, where multiple recordings are taking place in a simultaneous or sequential manner, or during interrupted recording sessions, to have a photoactive media that exhibits a true and controlled threshold for a recording event. This is desirable for a number of reasons, for example, to simplify the recording schedule, to improve image fidelity, to improve efficiency of polymerizing monomer or oligomer for recording holograms, to improve the handling quality and possibly improve pre-recorded shelf-life. Thus, initiation systems that can be activated in-situ in a specific location while the surrounding location(s) are left in an inactive state are provided. In such a system, the photosensitizer, the dye-like compound that imparts photosensitivity at a desired wavelength, can be activated or switched from a non-reactive state to a reactive state using an external stimuli such as light, heat or a combination of both. Once the dye compound has been switched or activated to the reactive state, the dye compound can be used as an actinic light sensitizer for initiation of a photopolymerization process, where such processes could be used for micro lithography or hologram recording.

[0090] In such a system the media would be prepared and conditioned so as to be nonreactive to a 1^st wavelength λ_\ , the wavelength of data recording or the desired wavelength for photo-activity. Recording data would follow the steps of (1) activating a region to be recorded by action of light of a second wavelength λ₂, or by the action of heat or a combination of both, (2) followed by data recording at the desired wavelength, λ_\ and (3); subsequently moving to a new recording location, say an abutting region or an overlapping region that is at least partially overlapping, where the process could be repeated. In the dye activation process the abutting regions are desirably inactive to the recording wavelength and thus abutting regions are not impacted by recording in neighboring areas. Even the spillover light due to the excess volume of illumination by the recording beams would desirably not cause pre-consumption of recording dynamic range in these regions. [0091] In such a system, the photosensitizer can be switched from a non- reactive state to a reactive state by a molecular reorganization such as exhibited, by way of example, in photochromic compounds. Such reorganization may be a cis-trans isomerization. In some embodiments, the re-organization is a cycloreversion process initiated by an external stimuli such as light, heat or a combination of both. Following the activation or switching process the dye compound can be used as a actinic light sensitizer for initiation of a photo-polymerization process, where such processes could be for hologram recording.

[0092] An initiator may also be introduced into a formulation for photopolymerization and holographic recording including monomers, oligomers, binders and the like, and said initiator can be introduced in a form that makes the media substantially nonreactive to a particular and desirable wavelength of light. In some embodiments, the initiator can be converted directly or indirectly to a new species either through action of light or heat.

[0093] In some embodiments, the initiator of the present invention is a photochromic compound that can be introduced into a formulation in an inactive state and that said initiator in the inactive state can be converted via a molecular reorganization to an active state by the action of light or heat.

[0094] Examples of photochromic compounds include but are not limited to:

Spiropyrans, spiro-oxazines, fulgides, triarylmethanes, quinones, naphthopyrans and diarylethenes. Diarylethenes are represented by stilbene, azoarene, diaryleperfluorocycloalkenes (butane, pentene, hexene), diarylmaleic anhydrides and diarylmaleimides and other such compound that undergo a reversible transformation, as indicated in the reaction scheme below, from a colorless to a colored form.

λl

A . B

X₂

Colorless Form Colored Form In some embodiments, a dye/sensitizer is coupled to a photochromic compound or switch, wherein the dye is attached via a linking group defined above.

[0095] In one embodiment, after the initiator is converted into the active state, the formulation will be reactive when exposed to actinic radiation of a desirable wavelength and that photopolymerization can occur.

Recording Wavelength λ{A λ₃ Energy Transfer

A . B *- I B

Inactive Form ^2 Active Form

Excited State Initiation/polymerization

[0096] In some embodiments, the initiator is a photo-sensitizer that interacts with a photoacid generator, photobase generator or photoradical generator to provide an initiating species when the initiator is in the active form.

[0097] In some embodiments, the heat process can be initiated via a direct method such via radiant heating. For example, the heat process can be initiated via an indirect methods by incorporation of an IR of NIR sensitive dye or a colloidal metal particle and use of an IR source or a visible light source, such as laser diode. The heat step may be done via secondary process where a laser source such as an IR or near IR laser can be used to heat a location in the storage medium thereby causing a heat activated dye forming reaction. In some embodiments, the media can be made susceptible to IR or Near IR irradiance by incorporating an IR dye or colloidal metal particles to absorb said IR irradiance. In some embodiments, the IR dye can be attached to a nano-particle. In some embodiments, the precursor dye compound can be attached to a nanoparticle and that both the precursor and the IR dye can be attached to the same nanoparticle to facilitate the efficiency of dye activation.

[0098] Methods of reducing extinction coefficient or changing concentration of the compounds for photoinitiation can improve uniformity of developed refractive index modulation during recording as a function of depth into the recording material, however, photopolymerization is still initiated at the wavelength(s) used for recording the holograms and the extent of polymerization is directly dependent upon the magnitude of the irradiance, typically in units of mJ/cm , of the exposure used for recording. Consequently, photoinitiation of polymerization reactions occurs wherever light is incident in the volume of the material during recording, such as where the Reference beam and Object beam must overlap for formation of the interference pattern needed to record a hologram as well as where light incident from the Reference and Object beams does not overlap. Further, if the Reference beam is incident at oblique angles with respect to the optical axis of the Object beam, or if the said volume of overlap has varying cross-sectional area as a function of depth through the recording material, both of which can occur during recording of volume holograms and at least one such condition generally occurs for recording of volume holograms, then an excess of the volume at or near a selected storage location(s) is exposed to light that causes photoinitiation and thus occurrence of undesirable polymerization reactions. The effects of the said excess volume being exposed during a recording event is further compounded by the need to achieve as high a multiplexing number as possible for each storage location so as to achieve a high value for areal storage density, and thus a grouping of exposures are made in substantially the same storage location wherein each said exposure initiates polymerization reactions undesirably in the said excess volume.

[0099] Further, although areal density of stored information in a storage location can be increased by increasing the numerical aperture (NA) of the imaging optics due to concomitant reduction in the Nyquist aperture, defined as Ny '=1.2 '2 *2λf/δ, wherein λ is wavelength of recording light, /is focal length of imaging lens, and ^is pitch of the pixels of the encoding device such as a spatial light modulator (SLM), or the Rayleigh length for recording of microgratings, the degree of differentiation for cross-sectional area as a function of depth through the recording material also increases with NA. For example, for Fourier transform holograms the area of the Object beam at the Fourier plane in the recording material is Ny², but, by way of example, if the Fourier plane is at the center of the recording material than the area of the Object beam is larger at or near the top and bottom surfaces of the material. [0100] By way of example, a classical optical architecture for recording

Fourier transform volume holograms such as of binary data pages is depicted in FIG. 1, wherein the Fourier plane is at location (21) in the recording material and where/} = fi for the lens elements (2) and (3) in a 4f recording/reading geometry having SLM (1) and detector (4). The Reference beam depicted as (10), by way of example, is incident upon the storage location in recording material (8) at an oblique angle with respect to the optical axis (25) of the Object beam (20), and the Reference beam (10) is incremented by an amount Δθ_t for the case of planar-angle multiplexing over an aggregate range of incident angles Δθ, such as up to a largest incident Reference beam angle (9), wherein the magnitude of Δθ_t for the ith recorded hologram in a storage location is related inversely to the thickness of the recording material for a given optical geometry and wavelength.

[0101] The undesirable use of a portion of the limited number of available chemical reactions for hologram formation for each multiplexing recording event in a selected storage location, due to the said excess volume being exposed, is further exacerbated by the need to increase the thickness of the recording material so as to achieve larger values for areal density. The impact of increasing thickness on the said excess exposed volume is depicted in FIG. 2. Reference beam (10) of FIG. 1 needs to be oversized in its lateral dimension at front face of the substrate of media (5) by an amount x to compensate for it propagating at an oblique angle through thickness T_g of the front substrate (e.g. glass) of media (5), and by an amount x' to further propagate through the thickness (T_ph) of recording material (8) so as to intersect the edge of the cross-section area of the Object beam (20) at the back plane of the recording material (8), wherein d is the lateral dimension of the Object beam (20) and d' is the corresponding oversize amount at the front and back surfaces of recording material (8) that is needed to provide for overlap of the interaction volume of the Reference beam (10) and Object beam (20) throughout the thickness (T_ph) of the recording material (8). The said oversize amount is an excess lateral dimension that results in an excess volume being undesirably exposed. In FIG. 2 the lateral dimension of the Object beam (20) is depicted as being uniform throughout the thickness of the media (5), for purposes of simplification, whereas for Fourier transform holograms the lateral dimension is often a minimum in the center and is larger at or near the front and back surfaces of media (5), as shown in FIG. 3(a) and FIG 3(b), so as to maximize storage density. An adjustable blocking of a portion of the Reference beam can optionally be used to reduce the amount of scattered light originating from excess volume in the substrates that may propagate in the forward direction from the substrates of media (5) into recording material (8), wherein the dimension or size of the adjustable portion can be changed as a function of the incident angle of Reference beam (10).

[0102] By way of example, for a Reference beam incident on the media at non-perpendicular angles (i.e. oblique angles), the size of the excess lateral dimension exposed in the media during recording is proportionally affected by the thickness of the recording material, T_ph, for the range of Reference beam angles used during multiplexed recording up to the maximum angle as shown in Equation (3) as

tan (90 - θ_Reflnt) = T_ph/d' Eqn. (3)

where 0R_ef_Int is the maximum internal angle for the Reference beam (10) in recording material (8) such as for a grouping of planar-angle multiplexing recordings in a selected storage location in the material (8).

[0103] FIG. 3(a) is a schematic representation of one embodiment of the optical geometry of reference beam 10 and object beam 20, wherein object beam 20 is relayed by optical element 2 to HRM 8 and reference beam 10 is incident onto HRM 8 at oblique angles of incidence.

[0104] FIG. 3(b) illustrates a detail of FIG. 3 (a) at the area of impact of the beams 10 and 20 onto HRM 8. FIG. 3(b) depicts schematically in cross-sectional view an example case for recording Fourier transform data page holograms with 2- axis multiplexing methods wherein the parameters for purposes of calculation of areal density of recorded holograms are size of the SLM is N_SLM=1024 pixels having pitch δ= 12 microns, wavelength λ = 0.407μm, average refractive index of the recording material is n_ave = 1.52, the range of the external angles of the Reference beam is between 35-65 degrees from the perpendicular to the recording material, φ is the maximum internal cone angle of the FT intensity distribution for the Object beam, θκef_jnt is the maximum internal angle for the Reference beam for 2-axis recording methods, the minimum diffraction efficiency for two-axis recording of binary data pages is η_eff=\. Oe-3 for minimum acceptable signal-to-noise of the reconstructed multiplexed data page holograms for this exemplification, and the cumulative grating strength of the recording material in an isolated storage location is set for a dynamic range of 5 per 200 μm thickness of the recording material for this exemplification and is attainable in thinner materials by use of dual multiplexing methods such as, by of example, combination of planar-angle and out-of-plane angle multiplexing. The maximum internal cone angle of FT intensity distribution for the Object beam, φ, can thus be defined as

φ = sin ¹ {sin [tan⁴ (N_SLM * δ/2j)]/n_me } Eqn. (4)

and the excess lateral dimension of the Object beam, ΔW, at the top and bottom surfaces of the recording material reduces the areal storage density of recorded holograms due to the lateral dimension of the Object beam, W, being expanded to W at the surface as

W= W+2ΔW Eqn. (5)

The lateral dimension of the recording Reference beam, W", must therefore be set to

W '= W+2ΔW + T_ph * tan θ_Reflnt Eqn. (6)

so as to compensate fully for the oblique angle of incidence of the Reference beam to provide for overlap of the Object and Reference beams in the interaction volume of the selected storage location(s). Consequently, the excess lateral dimension of the exposure area at the storage location increases monotonically with the thickness of the recording material, T_ph, and, further, the dependence of areal storage density of multiplexed recording is diminished from the linear scaling of dynamic range of the recording material with material thickness, T_ph, that could otherwise be exhibited if no excess lateral dimension occurred for the exposure area during recording.

[0105] FIG. 4 shows illumination of a selected storage location in a holographic recording medium, in cross section view, by actinic radiation at a first wavelength, λ' that activates the said medium for the step of recording holograms. The lateral dimension of the exposure with actinic radiation at a first wavelength is shown as the dimension W corresponding to the minimum dimension of the object beam during recording in the volume of the selected storage location. In certain embodiments the said lateral dimension of the exposure with actinic radiation at a first wavelength can be smaller or larger than W. Further, in certain embodiments the lateral dimension can change its size through the thickness of the recording material at the selected storage location, such as due to converging or diverging wavefronts for said illumination, and, further, can have a shape that is not symmetric in the lateral dimensions. The exposure with actinic radiation at a first wavelength can have an intensity distribution that is a Gaussian intensity distribution in the volume of the selected storage location for activating the location to recording. In certain embodiments, the intensity distribution of the exposure with actinic radiation at a first wavelength can be a truncated Gaussian intensity distribution such that the intensity distribution has a lateral dimension that is less than or equal to the diameter of a Gaussian beam, di_/e2, measured at the 1/e² intensity point of the intensity distribution, wherein d is defined to be the diameter of the beam waist for a Gaussian intensity distribution. During subsequent recording in the volume of the said selected storage location, the lateral dimension of the exposure with actinic radiation at a first wavelength defines the lateral dimension that is activated for the overlap of the recording object and reference beams. Thus, hologram recording occurs within the overlap volume at the selected storage location, but only where the activating exposure with actinic radiation firstly occurred.

[0106] The light source providing for said illumination means can, by way of example, be a CW or pulsed or otherwise modulated laser such as a diode pumped solid state laser, or diode laser, or can be a continuous emitting or modulated light emitting diode, or a lamp or other suitable light source, or combinations thereof, and can optionally be tunable in wavelength. The illumination means for recording includes an optical system including a means for illuminating at least one selected location that has been activated for carrying out photopolymerization in the said location of the recording material, wherein the optical system providing for said illumination means for recording can comprise one or more optical elements that, by way of example, can be one or more lens, or mirrors, or waveplates, or beamsplitters or polarizers, or combinations thereof as needed for illuminating the said activated selected location with at least one wavelength for the purpose of recording at least one hologram, and the light source for the recording illumination means can be the same light source as for the illumination means to provide for the threshold or activation event or can be another suitable light source that, by way of example, can be a CW or pulsed or otherwise modulated laser such as a diode pumped solid state laser, or diode laser, optionally with temperature controlled external cavity, or can be a continuous emitting or modulated light emitting diode, or a lamp or other suitable light source, or combinations thereof, and can optionally be tunable in wavelength.

[0107] The effect of the excess lateral dimensions of the Object beam and of the Reference beam can be represented as shown in FIG. 5 as a function of increased thickness of the recording material for the parameters defined above. The plot shows the theoretical relation between achievable storage density in bits/μm and thickness of the recording material in μm when the requirements for excess lateral dimensions of the Reference beam and Object beam are not considered for achieving optimal overlap throughout the depth of the material. FIG. 5 further shows the diminution in achievable storage density for the case of planar-angle multiplexing, when all of the dynamic range in a storage location cannot be consumed due to the limitations imposed by Bragg selectivity criteria as a function of thickness of the recording material, and additionally for the case of dual multiplexing when all of the dynamic range can be consumed in a storage location for a value that linearly scales as 5/200 μm thickness. [0108] Thus, the achievable cumulative grating strength for the ensemble of multiplexed volume holograms recorded in a selected storage location is undesirably substantially reduced from what otherwise could be achieved if excess lateral dimensions were not required for proper overlap of the Reference and Object beams in the interaction volume of the storage location, and, further, the scaling of achievable storage density versus thickness of the recording material, T_ph, is clearly not linearly increasing with the thickness, T_ph, as otherwise expected from the theoretical relation between cumulative grating strength, storage density and thickness.

[0109] In some embodiments, a method for photoinitiation of polymerization during recording volume holograms, in accordance with the method and apparatus of the present invention, is to threshold or activate the holographic recording events by (i) providing for a recording material that is otherwise not sensitive or is inactive to the recording and/or reading wavelength(s) until the threshold or activation event has occurred, and (ii) further providing a means to create and/or control the amount of the photoinitiator or sensitizer compound(s) that is formed in the recording material in one or more selected storage locations in an induced activation event prior to and/or at the time of recording, for the expressed purpose of activating photoinitiation processes that can be used to initiate polymerization reactions during the recording of holograms, or otherwise activate polymerization reactions for recording of holograms, particularly in the case of thicker materials, wherein the said created amount (i.e. concentration) is at least the amount of the photoinitiator or sensitizer compound required for any specific holographic recording exposure or desired grouping of exposures that record at least one hologram(s) at the recording wavelength, such as in a grouping of multiplexed recording events.

[0110] For example, it is desirable to threshold or activate the hologram recording process in one or more selected locations so that the recording material is substantially insensitive or inactive to the recording or reading laser light wavelengths in said one or more selected locations unless and until the said threshold or activation event has occurred in said locations. In this manner reading from media that is not fully recorded (i.e. chemistry of recording can still occur), such as reading from storage locations previously recorded along an z⁴ track when recording can still be carried out elsewhere on the z^th track or in another track or location that may be abutting or at least partially overlapping or otherwise affected by light incident from scattered light, fluorescence, stray light, oversized area of illumination compared to the area of the stored information, or other sources of incident light that arise during recording at and/or reading from said locations in the z^th track, does not alter the ability to record or write information later in locations along the z^-th track or proximal tracks of said media.

[0111] Additionally, during recording at least portions of the Reference beam light are typically incident upon the recording location at an oblique angle(s) and the cross-section area illuminated by the Reference beam should preferably be at least the size of the cross-section area illuminated by the Object beam throughout the interaction volume of the selected storage location. Consequently, the reference beam covers an area at or near the front of the recording material that is displaced laterally from the area it exits or impinges upon at the opposing surface of the said recording material. The effect of the said lateral displacement, as described above, is that the Reference beam is preferably oversized relative to the Object beam such that the cross-section area of its illumination overlaps the cross-section area of illumination of the Object beam at all depths throughout the said recording material in which the recording is to occur. Similarly, if the Object beam is incident upon the recording material at angles more oblique than the Reference beam then the Object beam is preferably oversized relative to the Reference beam.

[0112] In the general case of linear absorber compounds used for photoinitiation reactions in holographic recording materials, the oversized Reference or Object beam causes photosensitization and thus initiation of polymerization reactions to take place in a cross-section area that is larger than the cross-section area corresponding to the holographically stored information at substantially all depths in the selected storage location in which the recording is to occur. The undesired polymerization reactions in the volume of the selected storage location wastes chemistry that can otherwise be utilized for formation of holograms at one or more storage locations, so as to maximize areal density in said locations, and, consequently, the undesired reactions can reduce recording sensitivity and achievable dynamic range, and thus substantially limit the attainable storage density. This undesirable effect is exacerbated as thickness of the recording material is increased.

[0113] In another aspect, a method and apparatus are provided for photoinitiating polymerization or otherwise initiating polymerization for holographic recording in one or more selected locations in a recording media such that the initiation of polymerization reactions for recording holograms in said locations exhibits a threshold to the recording wavelength(s) provided by the optical system of the apparatus. In some embodiments, the one or more selected locations in the recording media are substantially insensitive or inactive to the wavelength of recording laser light provided by the optical system of the apparatus unless and until the threshold event for sensitizing the medium to the recording wavelength(s) has firstly occurred in the one or more selected locations. Herein, the term "insensitive" or "inactive" shall mean a chemical state of the medium, such as a photochemical state of the medium, or conformational state of molecular compounds in the medium, or other chemical or physical chemical structural state of components of the medium, in which photoinitiation of polymerization of the polymerizable compounds in one or more selected locations in the recording material for recording holograms is substantially insensitive or inactive to light at the recording wavelength(s) that is incident said locations unless the threshold or activation event that results in activating the medium so that polymerization events can be initiated using the wavelength(s) of the recording laser light to record holograms has firstly occurred. By way of example, the threshold or activation event of the present invention and the recording events for recording holograms may occur sequentially or simultaneously in a selected storage location in the recording medium, or may occur sequentially or simultaneously in a grouping of selected storage locations in the recording medium. By way of example, the required said threshold event for creating an active chemical state in at least one selected location in the recording medium for sensitizing the selected volume in the recording medium to record holograms at the recording wavelength(s) provides the means to prevent or otherwise substantially mitigate the effects of the excess lateral dimension of the Reference beam and, optionally the Object beam, from diminishing the areal information density that is achievable if such said excess dimension did not occur and, further, prevent or substantially diminish undesirably consuming monomer intended for polymerization reactions that are optimally for recording holograms.

[0114] According to various embodiments, the threshold event for sensitizing the medium to the recording wavelength(s) can preferably occur by use of light and/or heat for in- situ creation of the desired population of the active compound(s) in the volume of a selected storage location, said created active compound to be subsequently utilized for the process of photoinitiation of polymerization or other means of initiation of polymerization at the recording wavelength in the said volume of said storage location so as to provide a means for recording holograms at the recording wavelength. By way of example, the in-situ created active compound resulting from the said threshold or activation event can act as a linearly absorbing dye compound for photoinitiating polymerization reactions for the purpose of recording holograms, such as, for example, by the methods of free radical, cationic, anionic or step polymerization reactions. Alternatively, the in-situ created active compound resulting from said threshold event can act directly, such as, for example, by formation of a compound capable of acting as an acid or base or radical initiator, to initiate polymerization reactions for recording holograms in the selected storage location. Preferably, but not required, the population or concentration of the in-situ created active compound is both controllable by the threshold or activation event and, additionally, relates to the subsequent recording sensitivity in the selected storage location. The selected storage location for inducing the threshold event for in situ creation of the active compound may be a location at any position in the recording media, that, by way of example, can be any position about the area of the media such as any position along a tangential, radial or helical direction, or row or column direction, and, further, the induced threshold event at said selected location may occur throughout the thickness of the recording material at the selected location, or at any thickness location or position within the recording material that includes a thickness that is less than the thickness of the recording material such as may be desired for recording information in one or more layers in the recording material. [0115] If the induced threshold event for in- situ creation of the active compound at a selected location in the recording media occurs throughout the thickness of the recording material, then the population or concentration of the in situ created compound can be substantially uniform throughout the thickness of the recording material or, alternatively, can be non-uniform such as, for example, to compensate for the transmission function of the recording light that propagates through the recording material and may be used during recording of one or more holograms at the selected storage location. The size of the selected location in the recording material for inducing the threshold or activation event for in situ creation of the active compound may be a size that is equal to or substantially similar to the desired area of the selected storage location for recording one or more holograms, or the size may be an area that is larger or smaller than the desired area of the selected storage location for recording one or more holograms. If the threshold or activation event occurs by use of light incident upon one or more selected locations of the recording medium, then the wavelength of light for inducing the threshold or activation event is preferably different from the wavelength used for recording or reading the holograms, so that illumination of a selected storage location that is not firstly prepared or activated by the said threshold event results in substantially no polymerization reactions for recording holograms.

[0116] A grouping of other advantages can be realized by the method and apparatus, according to various embodiments. For example, by providing for inducing or creating the said threshold or activation event at a selected location(s), the storage system can further provide for direct read after write capability to verify recording of holograms with suitable diffraction efficiency and/or signal-to-noise characteristics, such as may be desired for purposes of error checking, alignment tracking or checking, in-situ evaluation of recording sensitivity and/or remaining dynamic range in a storage location, adjustment of exposure times or intensity of exposure, and the like. Further, the design of apertures for defining lateral dimensions of recording area at a storage location and/or reading from one or more storage locations can be substantially simplified. Said apertures of the apparatus and method of the present invention may be different sizes for the illumination wavelength(s) used for the threshold or activation event by comparison to the illumination wavelength(s) used for recording or reading holograms. Still further, the media of the apparatus and method of the present invention can be encased or otherwise protected in a cassette or other suitable holder that is primarily used to protect it from dust, dirt, particulate, scratching, etc., rather than from exposure to light having the recording or reading wavelength.

[0117] Still further, the recorded holograms by way of the induced said threshold event can exhibit improved uniformity of refractive index modulation achieved during recording as a function of depth into the volume hologram, particularly for thick recording materials on the order of 500 microns or thicker. By way of example, the optical density in the volume of the storage location, whether throughout the thickness of the recording material or in one or more layers in the material, can be optionally tuned or controlled in relation to the created population of the active species for photoinitiation for each recording event or a grouping of recording events specifically for the recording sensitivity that is needed or otherwise desired for said recording event(s). For example, the in-situ tuning of the optical density for recording events at one or more selected locations can take into account the declining population of monomer in the volume of the selected location(s), as well as other consumable compounds that may be part of the photoinitiation or other initiation process for the polymerization reactions, so as to provide for more uniform recording sensitivity throughout the manifold of the grouping of multiplexed recordings in the selected storage location. Further, the threshold event for creation of the population of the active species for photoinitiation of polymerization reactions for holographic recording events can be optionally carried out from the reverse direction of the propagation direction of the Reference and/or Object beams for recording holograms, so as to further compensate for absorbance effects on intensity of transmitted light through the thickness of the recording material during recording events. The deleterious impact of exposure of the recording material to stray light during recording or direct read after write or reading of holograms in the same storage location or nearby storage locations can be substantially diminished or eliminated. Further, recording sessions can be interrupted along a recording track, whether along tangential or radial directions or other suitable directions over the surface area of the media or the thickness direction in the recording material, and may even be interrupted within a selected storage location for advantageous recording of smaller amounts information then by comparison to restrictions imposed by single recording sessions for an entire media or for recording sessions carried out along one or more tracks in tangential or radial directions or along row or column directions, or carried out in one or more layers or in one or more directions within one or more layers.

[0118] According to one embodiment of the method and apparatus, it is provided to threshold or activate volume holographic recording by providing for a recording material that is otherwise not sensitive to the recording and/or reading wavelength until the threshold or activation event has occurred, and to control the amount formed of a sensitizer compound or other compound, in one or more locations in the recording media, to the amount of an active compound that is needed for any specific multiplexed holographic exposure or grouping of exposures for recording holograms at the recording wavelength, wherein the holograms can be recorded throughout the thickness such as for the case of binary data page holograms or, alternatively, in an increment of thickness such as corresponding to the double Rayleigh length that relates to the thickness of micro-localized gratings.

[0119] By way of example, heat and/or a first wavelength can be used to activate or pre-sensitize the recording media in the volume of a selected storage location that is to be used subsequently for one or more recording events, and the media can, preferably, be substantially insensitive or inactive to the recording wavelength until the threshold or activation event occurs. The threshold or activation event can comprise application of heat and/or illumination of the recording media at the one or more desired selected storage locations, such as with a diode laser, light emitting diode, diode pumped solid state laser, flash lamp and the like, that outputs light at a first wavelength or grouping of first wavelengths hereinafter referred to as first wavelength. By way of example, the apparatus and method of the present invention can provide illumination with a diode laser, light emitting diode, diode pumped solid state laser or flash lamp at a first wavelength and can, by way of example, use one or more lens elements or one or more reflective optical elements, or combinations thereof, or other suitable optical components including, for example, beamsplitters, waveplates, gratings, dichroic films, optical filters, polarizers and the like to provide said illumination.

[0120] Said first wavelength can be longer or shorter than the wavelength used for hologram recording or reading, such that substantially no absorbance exists at the recording or reading wavelength at the selected location for active initiation of polymerization reactions prior to the induced threshold or activation event, or optionally only nominal low absorbance exists near the recording or reading wavelength prior to the threshold event, wherein the said nominal low absorbance can only result in slow photoinitation induced polymerization or other initiation induced polymerization reactions, or substantially incomplete polymerization reactions at the recording or reading wavelength. In one embodiment, the threshold or activation event can comprise illumination at a combination of 1^st wavelengths, such as in a stepwise fashion, or, alternatively, simultaneously such as emitted, by way of example, from a light emitting diode or flash lamp or from two or more light sources that output light of different wavelengths, wherein the 1^st wavelengths are longer or shorter than the recording or reading wavelength such that substantially no absorbance exists at the recording or reading wavelength, prior to the threshold or activation event, that can activate initiation of polymerization, or only nominal low absorbance exists near the recording or reading wavelength prior to the threshold event such that substantially no photoinitation induced polymerization, or relatively slow photoinitation induced or other initiation induced polymerization reactions occurs at the recording or reading wavelength, or substantially incomplete polymerization reactions occur at the recording or reading wavelength.

[0121] The shape of the exposed area at a selected storage location when illuminated by the 1^st wavelength to induce the threshold or activation event for formation of the desired photoinitiation or initiator compound can be a circle or square or rectangle or diamond or oval or other suitable shape. In FIG. 3(b), by way of example, the area at the Fourier plane for recording data page holograms in the recording material (8) will be W as it will be a square of dimension W on all sides corresponding the Nyquist aperture. The exposed area at the top or bottom surface of the recording material (8) can similarly be a square of area W , and the illumination at the said 1^st wavelength can propagate through the depth of the recording material (8) so as to have a uniform cross section area of W at all depths within the material, as shown in FIG. 4. This can be achieved, for example, by use of collimated illumination for said 1^st wavelength. Alternatively, the exposed area can be within the material at a certain depth position in the material, and can extend through the depth dimension by an amount that exceeds the lateral dimension of the exposed area but is less than the total thickness of the recording material, such as would be the case for recording micro-localized gratings wherein the lateral dimension of the exposed area for a typical micrograting is on the order of about 200 nm to 1000 nm.

[0122] In another aspect, the direction of said illumination at said 1^st wavelength for the threshold or activation event can be the same direction as the propagation of the Object beam and/or Reference beam used during recording of the volume holograms in the storage location. Alternatively, the direction of the said illumination at said 1^st wavelength for the threshold or activation event can be in the opposing direction to the propagation direction of the Object beam and/or Reference beams so as to provide for formation of a concentration profile of the photo initiation compound created by the threshold event, said profile being in the reverse direction of the transmission function occurring during recording holograms. Further, in still another embodiment, the cross section area of the illumination at the said 1^st wavelength at a storage location can match the profile of the Object beam through the recording material. In FIG. 5, plotted with symbol (♦), is the relation between achievable storage density in bits/μm and thickness of the recording material in μm when a threshold or activation event is utilized with illumination at a said 1^st wavelength that has uniform cross section area throughout the thickness of the recording material that equals the area at the Fourier plane for the Nyquist aperture. The effect of the said threshold event on achievable storage density versus thickness of the recording material is to substantially increase the storage density from what is otherwise achieved when no method of threshold event is used. [0123] A recording material can, by way of example, comprise a uniformly dispersed dye compound, or a dye compound adsorbed to the surface of a particle, such as a nanoparticle or core-shell particle that is dispersed in the material. Said dye compound, by way of example, can be a Near Infrared (NIR) dye or Infrared (IR) dye compound that absorbs NIR or IR light, respectively, or can be a compound that absorbs in the short to middle range of visible wavelengths (i.e. about 380 nm to 620 nm) such as, by way of example, a compound including at least one substituted or unsubstituted napthalene or anthracene or phenanthrene, or pyrene or naphthacene grouping, wherein the conjugation length of the said substituted or unsubstituted groupings can be optionally extended by way of donor/acceptor chemical structure or functionality or by at least one substituted or unsubstituted ethynyl or ethenyl grouping, or at least one substituted or unsubstituted bisethynyl or bisethenyl grouping, or at least one substituted or unsubstituted phenyl or thiophene or furan or pyrrole or pyridine grouping, or the compound can absorb in the long visible wavelengths (i.e. about 620 to 750 nm) such as a compound including at least one substituted or unsubstituted pentacene grouping. Further, the dye molecule can be part of a larger molecule including chemical structure that undergoes other chemical or photochemical or stereochemical or conformational processes or changes, including, by way of example, changes in molecular or chemical structure such as geometric isomerization and rearrangement, ring opening, ring closure, formation of cyclic products or intermediates including bicyclic products, such as by cycloaddition reactions, wherein said processes or changes, by way of example, can be related to the wavelength and/or intensity of light that illuminates the recording material at the selected location(s) and said processes or changes may, optionally, be reversible or partially reversible between two or more chemical or photochemical or structural states.

[0124] In one embodiment, the recording material includes a compound that can be chemically or structurally altered by exposure of one or more locations in the recording material to UV, or visible, or NIR or IR radiation, or combinations thereof, such as in a stepwise process, or alternatively simultaneously, so as to form the desirable active species during the threshold or activation event for photoinitiation of polymerization or other initiation of polymerization in the recording material at the recording wavelength. Said active species (activated dye compound) can, for example, further react at one or more selected locations in the recording medium due to oxidation reactions of the compound or oxidation/reduction reactions that can involve one or more other compounds and in one embodiment thereby initiate polymerization of one or more monomers or oligomers. In one embodiment, the formation of the active species for photoinitiation of polymerization in the recording material at the recording wavelength can, alternatively, occur due to presence of oxygen, or to reducing or substantially eliminating the presence of oxygen, or to reducing or substantially eliminating the population of other molecule(s) that can act as a retarder(s) or inhibitor(s) to slow or prevent photoinitiation processes for initiating polymerization in the one or more selected locations of the recording material. The compounds that act as a retarder or inhibitor may additionally be diffusible in the recording medium. In one aspect, oxidation/reduction reaction(s) of the compound can occur due to reactions with a suitable photoacid generator that does not form sufficiently strong acid for initiating photopolymerization of siloxy silane epoxy compounds or vinyl ethers and the like.

[0125] According to some embodiments, the amount of the in-situ formed absorber species that is formed during or after exposure to said 1^st wavelength can preferably be tuned or controlled to the amount required to achieve suitable recording sensitivity for a particular exposure fluence, or tuned or controlled for the population of monomer that can polymerize in the volume of the interaction volume of the Object and Reference beam wherein the population can change during a sequence of recording events utilizing co-locational multiplexing, or tuned or controlled for the population of other compounds that can participate in the photoinitiation process for polymerization reactions in the said interaction volume, and the like, such as in a sequence of multiplexed holographic recordings. This metering process for in-situ formation of the active compound, implemented by intensity and/or time conditions for the exposure with the said 1^st wavelength, can be particularly advantageous for achieving high fidelity in thicker recording materials. It can also provide for direct read after write capability, such as may be used for evaluating BER of recorded holograms, and can be advantageous for achieving more uniform recording sensitivity during a sequence of multiplexed recording event, as well as tuning or controlling other holographic performance attributes.

[0126] Alternatively, compounds for the threshold event can absorb short wavelength radiation, such as UV radiation, that causes chemical structure change and formation of a new compound that absorbs at the recording wavelength or some other visible wavelength that can be additionally be used for illumination of the volume at the selected storage location and thereby create the compound for photoinitiation or other initiation of polymerization at the recording wavelength. Still further, the compound formed from the threshold or activation event can optionally be reversibly converted back to the species that is inactive at the recording wavelength, and then converted again by another threshold or activation event to the compound that can photoinitiate or otherwise initiate polymerization during hologram recording.

[0127] In one embodiment of the apparatus and method, the same optical system, or portions of the same optical system, used for delivering the Object beam to the selected location(s) in the recording material can be used for delivering the irradiation from the said 1st wavelength that is used for activation. A longer 1st wavelength would result in longer focal length due to dispersion of the refractive index of the glass materials used for optics, but the spot sizes would not differ significantly for the two wavelengths for suitable optical designs. Similarly, a shorter 1^st wavelength would result in shorter focal length due to said dispersion. Alternatively, a separate optical element or optical system or portion of an optical system can be used for delivering the said 1^st wavelength to a storage location for the threshold or activation event. Still further, in another embodiment of the apparatus and method, the threshold or activation event can be carried out as part of a servo system, such as used for tracking, addressing and/or alignment, that can optionally interact with the media at locations forward of the recording events such that activation occurs prior to recording. An optical system of the apparatus can be designed advantageously with approximately equal focal lengths for both wavelengths, or to provide for a correction using one or more other optical elements, optionally adaptive optics, so that when the two wavelengths are coupled in the same optical path then the focal distances would be similar for optimizing the similarity of the areas of illumination.

[0128] FIG. 6 is a plot showing diffraction efficiency, η, as a function of recording exposure energy E. Diffraction efficiency, η, in a selected location in the recording material does not change and is nominally a value of zero as a function of exposure energy at a recording wavelength λ₂ until an activation event occurs at the selected location at the activation or threshold wavelength X_\. Further, η, in the selected location in the recording material does not change and is nominally a value of zero as a function of exposure energy at the said activation wavelength λ_\. Once suitable exposure has occurred at the activation wavelength λ_\ to create or otherwise induce the threshold or activation event required to record one or more holograms at the selected location, then holographic exposure at the recording wavelength λ₂ can form hologram(s) that exhibit a value of η that is related to the magnitude of the exposure energy at the recording wavelength X₂. Thus, η_Ε and η_El can represent two values of η achieved for two values of recording exposure energy E_a and E_b, respectively, in mJ/cm², wherein Eb > E_a and the exposure energy E_a and Eb occur at the recording wavelength X₂.

[0129] Further, the magnitude of exposure in mJ/cm² at the activation or threshold wavelength

can influence the magnitude of η achieved at the recording wavelength λ₂ for two values of activation exposure energy E_a and E_b at the activation wavelength X_\. For example, if activation exposure energy at wavelength X_\ for purposes of activation at a selected location forms a compound having a population that is sufficient to activate polymerization at wavelength X₂, but only for recording a portion of the whole dynamic range of the material at the selected location on the basis of the population of monomer that can polymerize if full activation was achieved, then, by way of example, a diffraction efficiency of η < η_Ε can occur for an energy of E_a for the activation or threshold event for the range of exposure energy at the recording wavelength X₂. Similarly, if the exposure energy at X₁ is E_b for the activation or threshold event, and Eb provides for an activation state at a selected location that is greater than the activation state provided for by E_a, but the formed compound has a population that is insufficient to fully activate polymerization at wavelength λ₂ on the basis of the population of monomer that can polymerize if full activation was achieved, then a diffraction efficiency of η < η_E can occur for an energy of Eb for the activation or threshold event for the range of exposure energy at the recording wavelength λ₂.

[0130] The present technology, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration and are not intended to be limiting of the present technology.

EXAMPLES

[0131] Scheme 1 illustrates a general procedure that may be used for the preparation of switch compounds, according to various embodiments.

Scheme 1 :

[0132] Compounds A, B, E, and G are commercially available from Sigma-

Aldrich. Compounds C and D may be prepared according to the procedure set forth in Macromolecules, (2003), p. 298-303. Compounds H, J, and K may be prepared according to the procedures as set forth in J. Am. Chem. Soc. (2006), pl3680-13681 or Org. Lett. (2003), 3195-3198.

[0133] Preparation of Compound F: To a dry 200 mL flask under argon was charged 2,4-dibromo-5-methylthiophene (12.80 g, 50 mmol). The flask was then evacuated and refilled 3 times with argon, and anhydrous tetrahydrofuran (100 ml) was added via cannula. The solution was cooled to -78°C and n-butyl lithium (20 niL, 2.7 M, 54 mmol) was added slowly over 15 minutes. After the addition was complete, the mixture was stirred for 15 minutes at -78°C. Triisopropylsilyl chloride (12.2 mL, 57 mmol) was then added at -78°C and the reaction slowly warmed up to room temperature overnight and stirred for three days. The solvents were removed in vacuo and the solid applied to a silica hexanes column. The fractions were collected and the solvents removed in vacuo. The product was recrystallized from isopropanol and dried under vacuum at 60⁰C. A second recrystallization from isopropanol afforded compound (F) as white crystals (10.0 g, 60% yield; m.p. 58-60⁰C).

[0134] Preparation of Compound Sl : A dry 100 mL round-bottom flask was charged with compound F (2.38 g, 7.14 mmol) and tetrahydrofuran (50 ml), cooled to -78°C and n-butyl lithium (2.8 mL, 2.7 M, 7.6 mmol) was added slowly. The mixture was then stirred for 15 minutes at -78°C. Compound D was then dissolved tetrahydrofuran (8 ml) and added to the mixture at -78°C. To reaction was then stirred for 30 minutes, followed by slow warming to room temperature overnight. Solvent was stripped and silica hexanes column separation afforded a yellow oil product, 2.89 g Sl (72% yield).

[0135] Preparation of compound S2 : Compound Sl (1.19 g, 2.15 mmol) was dissolved in dichloromethane (100 ml) in a 250 mL flask and cooled to -20⁰C. Triflic acid (0.5 mL) was then added and the reaction warmed to room temperature, followed by stirring for one hour. The solvent was then removed in vacuo and solid applied to a hexanes silica column. Separation afforded compound S2 (0.850 g, 98%) as a clear colorless oil.

[0136] Preparation of compound S3 : Several attempts were made to run this bromination in dichloromethane/acetic acid mixtures but these produced incomplete reactions. These incomplete reactions were combined, approximately 2.5 mmol, dissolved in 15 mL N,N-dimethylformamide. Excess N-bromosuccinimide (620 mg, 3.5 mmol) was then added and the mixture stirred overnight in the dark. The DMF was removed in vacuo and the solid applied to a silica hexanes column separation to afford compound S3 (1.145 g, 2.38 mmol, 95% yield). [0137] Preparation of Compound S4: A dry 50 mL round bottom flask was charged with compound K (1.75 g, -3.2 mmol), compound S3 (1.10 g, 2.3 mmol), tris(dibenzylideneacetone) dipalladium (105 mg, 0.11 mmol, 10 mol% Pd) and triphenyl phosphine (240 mg, 0.92 mmol). The flask was evacuated and refilled three times with nitrogen, and then anhydrous, de-gassed toluene (25 ml) was added and the reaction was de-gassed for 5 minutes with nitrogen. The reaction mixture was heated to 115°C for 30 minutes. Silica TLC in hexanes indicated a new purple switch compound and consumption of starting bromo-chloro switch compound S3. The reaction was mixture was cooled and stirred at room temperature overnight. The toluene was then removed in vacuo and the solid applied to a silica/hexanes column. The fractions were collected and the solvent removed in vacuo. The solid was then boiled in methanol, cooled and filtered. After dried under vacuum compound S4 (1.00 g, 75% yield) was recovered.

[0138] Preparation of compounds S5 (using compound S5a as an example):

Switch compound S4, (58 mg, 0.10 mmol), arylboronic acid (0.2 mmol), tris(dibenzylideneacetone) dipalladium(O) (5 mg, 10 mol% Pd), SPhos (9 mg, 20 mol% L)and anhydrous potassium phosphate tribasic (85 mg, 400 mol%) were placed in a dry 3 mL vial with Teflon septum screw cap and evacuated/refilled three times with argon or nitrogen. De-gassed, anhydrous n-butanol (1 ml) was added and the mixture heated overnight at 100⁰C. The reaction mixture was then cooled, the solvent removed in vacuo, and the crude product applied to a silica column packed in hexane. The column was then eluted with a gradient of methylene chloride/hexanes (5% 100 mL, 10% 100 mL, 20% 100 mL). The pure fractions were combined, the solvent again removed in vacuo, and methanol was added to form a slurry. The slurry was transferred to a centrifuge tube and stored in the freezer overnight. The slurry was then centrifuged cold and decanted. The light green solid product was dried under high vacuum to afford ~25 mg (-40% yield) product. The final structures of the grouping of molecular switch products were confirmed by NMR.

Compound S5-a was characterized by ¹HNMR (400 MHz, CDCl₃): 1.254, 1.554 (a, b); 1.934, 1.982, 2.491 (1); 6.668, 6.671, 6.677, 6.680 (k); 6.959, 6.967, 6.974, 6.983, 6.999, 7.008 (j, i, h); 7.270 (f); 7.283, 7.302, 7.320 (e); 7.308, 7.388, 7.407 (d); 7.534, 7.553 (c); where the protons are assigned as:

Compound S5-b was characterized by ¹HNMR (400 MHz, CDCl₃): 1.935, 1.962 (a, b); 2.489, 2.490 (1); 3.837 (c); 6.667. 6.670, 6.676, 6.679 (k); 6.903, 6.925 (e); 6.958, 6.966, 6.972, 6.982, 6.996, 7.005 (j, i, h); 7.109 (g); 7.144 (f); 7.454, 7.476 (d); where the protons are assigned as:

Compound S5-c was characterized by ¹HNMR (400 MHz, CDCl₃): 1.964, 2.0303 (a, b); 2.488 and 2.491 (k); 6.669, 6.672, 6.678, 6.681 (j); 6.957, 6.996 (i); 6.976, 6.985 (h); 7.001, 7.011 (g); 7.090 (f); 7.402 (e); 7.791, 7.923 (d); where the protons are assigned as:

Compound S5-d was characterized by ¹HNMR (400 MHz, CDCl₃): 1.948, 2.003 (a, b); 2.489, 2.491 (m); 6.669, 6.672, 6.677, 6.680 (1); 6.958, 6.967, 6.975, 6.984, 7.001, 7.009 (k, j, i); 7.102 (h); 7.331 (g); 7.491, 7.510, 7.529, 7.545, 7.565 (d, c); 7.700, 7.720 (e); 7.758 (f); where the protons are assigned as:

[0139] Asymmetric switch compounds may be prepared according to the example provided by Scheme 2.

Scheme 2:

[0140] The dibromo-switch (S6) (520 mg, 1.0 mmol), was charged to an argon-flushed 50 ml three neck reaction vessel equipped with a magnetic stir bar, a reflux condenser, an argon inlet/outlet and a thermometer. PdCl₂(PPh_S)₂ (22 mg) was then added along with toluene (12 ml), and Na₂CO₃ (700 mg) dissolved in H₂O (4 ml). This mixture was degassed by flushing with argon for 10 min. While degassing 5'-hexyl-2,2'-bithiophene-5-boronic acid pinacol ester (L; Sigma- Aldrich) (400mg, l.Oβmmol) was dissolved in ethanol (4 ml) and then added to the reaction mixture. The reaction mixture was heated via an oil bath to an internal reaction temperature of 75°C and maintained at 75⁰C overnight. The reaction was then cooled and the solvent removed in vacuo. The crude product was then applied to a silica hexanes column run with gradient with methylene chloride (5% 100 mL, 10% 100 mL, 20% 100 mL). Pure fractions were combined and stripped to yield a dark colored solid which was dried under high vacuum to yield ~40 mg (~6% yield) of (S7). The structure of product (S7) was confirmed by ¹HNMR. Note that the ¹HNMR was obtained on the switch in the "closed" conformation by irradiating the ¹HNMR sample tube with UV light from an LED source for 1 hour. Compound S7- closed was characterized by ¹HNMR, which is provided as FIGs. 7A and B.

[0141] Other symmetric switch compounds may be prepared according to the example provided in Scheme 3.

Scheme 3:

[0142] The symmetric molecular switch compounds S8a/b with acetylene linking groups to the switch core were prepared following the general procedure below. [0143] A reaction vessel equipped with a stir bar was charged with S6 (100 mg, 0.19 mmol), ethynylarene ( 0.47 mmol), triphenylphosphine (22 mg, 0.08 mmol), tris(dibenzylideneacetone)dipalladium(0) (8 mg, 0.009 mmol), and copper(I) iodide (32 mg, 0.17 mmol). The vessel was fitted with a Teflon-septum screw cap and evacuated/refilled three times with nitrogen. De-gassed triethyl amine (1 mL) was added via syringe and needle. The reaction was then degassed with nitrogen for 5 minutes, sealed, wrapped in aluminum foil, and heated in an oil bath at 85°C for 4 hours. Then the reaction mixture was then cooled, filtered through Celite while eluting with triethyl amine, and then the solvent was removed in vacuo. The bis- anthracenylethynyl switch (S8a) was isolated by chromatography in 4% yield as a greenish solid (see ¹HNMR (400MHz) provided as FIG. 8). The bis- methoxynaphthylethynyl switch (S 8b) was isolated in 50% yield by recrystallization from toluene (MP 205-207⁰C), as a pale white crystalline solid.

Compound S6 was characterized by ¹HNMR (400 MHz, CDCl₃): 1.88 (a); 3.49 (b); where the protons are assigned as:

[0144] Comparative Example 1. Photosensitization of polymerization with

Thiophene Dye compound.

[0145] 5,5"-Dimethyl-2,2':5',2"-terthiophene (DMTT) was prepared by

Kumada coupling of 5-methylthien-2-ylmagnesium bromide with 2,5- dibromothiophene in diethyl ether with NiCl₂(dppp) (0.5 mol%) as the catalyst, analogous to the preparation of 2,2':5',2"-terthiophene (K. Tamao, S. Kodama, I. Nakajima, M. Kumada, A. Minato, and K. Suzuki, Tetrahedron (1982), 38(22), 3347). After chromatography through silica gel with dichloromethane, Soxhlet extraction from a 1 :1 mixture with silica gel with hexanes, and crystallization from hexanes, the product was obtained as yellow crystals in 77% yield, mp 101-103⁰C (literature mp 100-101⁰C, Ann. (1941), 546, 180-199).

[0146] A polymerizable formulation was prepared including the photo- sensitizer DMTT, 0.032%, and Rhodorsil PI2074, 4.8% in Diepoxy monomer PClOOO. The sensitization properties of DMTT for initiating cationic polymerization were evaluated using calorimetry (PDSC) as described below.

[0147] Cationic ring-opening polymerization is an exothermic process, therefore polymerization rates and extents of monomer conversion can be determined through calorimetry. Calorimetric analysis was performed on a Perkin- Elmer DSC-7 Differential Scanning Calorimeter equipped with an integrated DPC-7 Photocalorimeter Module including a medium pressure IOOW Hg lamp, transfer optics and a monochromator to control the wavelength of light exposure. Samples, 1.5-2.5 mg, were weighed into a standard DSC sample pan, placed into the calorimeter sample chamber and equilibrated at 30⁰C prior to illumination. After equilibration, samples were irradiated in the calorimeter with light at 407 nm from the Hg lamp using the monochromator, with incident intensity on the sample of 4.2 mW/cm . The heat flow required to maintain the sample at a constant temperature (30⁰C) was recorded at time intervals of 0.05 seconds. This data was integrated to determine the evolved heat of reaction versus illumination time which, after appropriate normalization, was converted to the extent of reaction versus time. The fractional extent of polymerization reaction as a function of time, φ(t), was then determined from the relation

QQ)

where q(t) is the heat evolved after illumination time t, and ΔH_rxn, the heat of light- induced reaction, is taken as the area under the complete corrected heat flow curve. [0148] The sample was subjected to an eight minute experimental protocol including three steps. The first step, from t=0 to t=2.0 minutes, establishes the baseline for isothermal condition of 30⁰C. The second step beginning at t= 2.0 min is initiated when a mechanical shutter opens and light from the monochromator is then incident on the sample and thereby irradiates the sample during the duration of this step from t=2.0 to t=7.0 minutes. Then at t = 7.0 min the shutter is closed and the baseline is reestablished, wherein the duration of the final step is one minute.

[0149] The PDSC results for DMTT sensitized photopolymerization with

407nm light are indicative of fast reaction kinetics, and are shown in FIG. 9. The onset of polymerization was determined to be at 2.032 min, corresponding to 0.032 min after the shutter opens. Peak enthalpy is achieved at 2.052 min, or 0.052 min after the shutter opened. The polymerization reaction is complete by 0.1 min (6 seconds), equal to 25.2 mJ/cm² exposure energy, with little or no further enthalpy of reaction realized with further light exposure.

[0150] Switch of Compound S7 with thiophene dye grouping

[0151] A sample of molecular switch dye compound S7, which includes a substituted thiophene dye grouping was dissolved in dichloromethane (DCM). Exposure of the open form, S7-open, in DCM solution to UV light (from an LED source), caused the compound to undergo a molecular switch to the "closed" form, S7-closed. The closed molecular switch dye compound S7-closed has a λmax at 568 nm.

[0152] General procedure for comparing the sensitization of the "open" form versus the "closed" form of the compound. [0153] The molecular switch was used as a sensitizer for photopolymerization of 1 , 1 ,3,3-tetramethyl- 1 ,3-bis-[2-(7-oxa-bicyclo[4.1.0]hept-3- yl)-ethyl]-disiloxane, (diepoxydisiloxane) with Bluestar Rhodorsil PI2074 photoacid generator.

[0154] The following procedure was used for testing the photosensitization performance for molecular switch dye compound S7 in the "open" and "closed" forms. A similar procedure was used to evaluate the other molecular switch dyes compound of this invention results of which are listed in Table 1, below.

Table 1.

[0155] A stock Dye formulation was prepared from S7-open (9.73mg) and enough diepoxydisiloxane to make 4.98893g of a stock formulation having 0.195 wt% of S7-open in the diepoxydisiloxane. A magnetic stir bar was added, stirring commenced and the stock Dye formulation was subjected to irradiance from UV light for 20 min from an LED source. The color of the Dye formulation changes upon exposure to light of 386 nm to dark blue, yielding a stock formulation including S7-closed.

[0156] Next, Bluestar, Rhodorsil® Photoinitiator 2074 (0.10551 g), was dissolved in diepoxydisiloxane monomer (2.10835g) to make a stock PAG formulation including 4.8 wt% PAG in diepoxydisiloxane monomer.

[0157] Next the stock Dye formulation (0.065g) including S7-closed was charged to a 1 dram vial, and stock PAG solution (0.39026g) was then added to the vial to yield Formulation I having 0.0276 wt% S7-closed and 4.7 wt% PAG in diepoxy monomer.

Photosensitization comparison:

[0158] A comparative study of the reaction kinetics of photo-initiated polymerization was done with the Formulation I using PDSC calorimetric analysis. The details of the PDSC equipment and method are described in the comparative example for photosensitization with thiophene dye. In the first experiment, an aliquot of Formulation I (1.5-2.5 mg) was weighed into a DSC sample pan that was placed in the PDSC test compartment. The sample was subjected to an eight minute experimental protocol including three steps. The first step, from t=0 to t=2.0 minutes, establishes the baseline for isothermal condition of 30⁰C. The second step beginning at t= 2.0 min is initiated when a mechanical shutter opens and light of 407 nm from the monochromator is then incident on the sample and thereby irradiates the sample during the duration of this step from t=2.0 to t=7.0 minutes. Then at t = 7.0 min the shutter is closed and the baseline is reestablished, wherein the duration of the final step is one minute.

[0159] In a second experiment, an aliquot of Formulation I (1.5-2.5mg) was charged to DSC sample pan and then the sample in the pan was irradiated for 5 min with light from a green DPSS frequency doubled YAG laser emitting at λ = 532nm. During irradiation, at the activation first wavelength (532 nm), the sample changed color from dark blue to almost colorless. Next the sample was subjected to a three step, eight minute experimental protocol for PDSC calorimetric analysis as described above.

[0160] The results of the two PDSC analyses are shown together in FIG. 10.

The results show that photosensitization with the molecular switch dye compound in the "open" form is rapid and complete in a short time period of less than 0.2 min. The photosensitization with the molecular switch dye compound in the "closed" form is, however, extremely slow and no appreciable photosensitized reaction occurs over the first 0.4 minutes of exposure equaling 100.8 mJ/cm exposure energy at 407 nm.

[0161] Preparation of a stock photopolymerizable Cationic Ring Opening

Polymerization (CROP) medium for holographic recording was formulated with asymmetrical molecular switch compound S5c. A binder of formula

where v and w total 4, 5, or 6, was charged to a vessel equipped with a magnetic stir bar. To the binder was added a difunctional epoxide monomer of formula R'- Si(RR)-O-Si(RR)-R' where each group R' is a 2-(3,4-epoxycyclohexyl)ethyl grouping; and each grouping R is a methyl group, and which is available from Polyset Corporation, Inc., Mechanicsville, NY., under the trade name PC-1000. The ratio of the binder to the di-functional monomer was 1. :46: 1.0. The mixture of binder and di-functional monomer was stirred to form a uniform homogeneous mixture. To this mixture was added a poly-functional monomer, referred to herein as C8 tetramer (see compound No. XXII US 6,784,300), in a ratio of 1.12:1 multifunctional epoxy to difunctional monomer, and the contents were stirred at room temperature to form a uniform mixture of a stock CROP formulation (SCF). Next, to S5c (1.4 mg) was added to enough SCF to make 0.6832 g of a new formulation comprising S5c at approximately 0.2%, SCF-Dye-open. This formulation was irradiated with UV light (LED source) for 6 hours to fully convert S5c to the closed form to yield SCF-Dye-closed. A second formulation was then prepared using SCF, and Rhodorsil PAG to make a formulation of 4.5% PAG in SCF.

[0162] Next, the SCF-Dye-closed was added to the 4.5% PAG in SCF formulation to yield a CROP formulation with -0.03% S5c-closed. The formulation was then filtered using an Acrodisc® CR25 mm Syringe filter with a 0.2 micron PTFE Membrane into an appropriate size storage container.

[0163] A card type media was prepared by first fixing two flat glass substrates disposed in a parallel, co-planar arrangement with a space or gap of 100 microns between the inner surfaces of the top and bottom substrates. Examples of methods for media assembly can be found in US 6,881,464. The formulation was coated between the two substrates using capillary forces. After complete filling of the "gap" the media was ready for further analysis.

[0164] Recording of nine co-locationally multiplexed slant fringe plane- wave transmission holograms was first attempted at the activation wavelength (X₁) using a frequency doubled Nd:YAG laser (Laser Quantum Model Torus 532-400) emitting at λ=532 nm. Two coherent spatially filtered and collimated laser writing beams were directed with an interbeam angle of 48.6° therebetween onto a sample recording media including material having thickness of about 100 μm sandwiched between two 0.55 mm thick polished glass substrates. The intensities of the two writing beams were equal at the condition of equal semiangles about the normal, and the total incident intensity for recording measured at the bisecting condition was about 8.25 mW/cm². The recording times of the schedule for recording the nine multiplexed holograms was consistent with recording energies used to record holograms in STX Aprilis Type D DHD® media of the same thickness for attaining moderately strong (~5% to -30%) diffraction efficiency for a small number of multiplexed holograms. (See, e.g., the STX Aprilis Type D DHD® media data sheet avalaible at "http://stxaprilis.com/TypeD_product-table_post2.pdf '). Results for the attempt to record holograms directly at the activation wavelength (X₁), prior to the step of in situ activation of the sensitizing compound for photopolymerization and/or hologram recording at a second wavelength, λ₂, exhibited no evidence of diffraction from the media, thus establishing that no hologram formation occurred for direct recording at X₁.

[0165] Similarly, no diffraction efficiency was detected when recording multiplexed volume holograms was attempted by directly carrying out recording exposures in the material at the recording second wavelength (λ₂) without having firstly forming the activated photosensitizer molecular switch compound by use of a first exposure at a first activation wavelength (X₁). Two coherent spatially filtered and collimated laser writing beams were directed onto the sample in the conventional manner for recording volume holograms (i.e. the recording beams were fully overlapped in the recording volume) with an interbeam angle of 51.3⁰A using a Sony Corp SBL single longitudinal mode blue-purple diode laser model emitting at 407 nm. The intensities of the two writing beams at the condition of equal semiangles about the normal to the sample were 2.3 and 2.5 mW/cm , and the total incident intensity for recording was 4.85 mW/cm² as measured at the bisecting condition. The recording times used were consistent with those conventionally used for multiplexing a similar number of plane wave volume holograms in STX Aprilis Type E DHD® media, [see D.A. Waldman, E.S. KoIb, and C. Wang, "DHD® CROP Holographic Storage Media for Advanced Optical Data Storage", Optical Data Storage (ODS), OSA Technical Digest Series, WDPD, 4-7 (2007)]. No evidence of hologram formation was detected.

[0166] This result shows an improvement over holographic media described in international patent application Ser. No. PCT/US2008/012034, the entire contents of which are incorporated herein by reference. In that reference, a formulation ("Formulation B"), comprising an anthracenyl molecular switch sensitizing dye compound in its closed "inactive" state" was sandwiched between two glass substrates with a 200 micron gap there between to form a holographic recording media having a thickness of 200 microns for the recording material. A selected location A in the media was exposed to actinic radiation at a first wavelength (532 nm) to form the active "open" state of the dye compound. Holographic recording at 407 nm, using a Sony diode laser equipped with a temperature controlled external cavity, was carried out in the activated storage location of media using planar angle multiplexing methods with collimated signal and reference beams having intensity of 4 and 3.5 mW/beam. The observed diffraction efficiency for 3 multiplexed holograms was 34.0, 33.5 and 42.8 %, respectively, corresponding to a recording sensitivity of 2.1, 1.98 and 2.0 cm/J respectively. A comparative recording of holograms was carried out on different selected location B in the media, wherein location B was not firstly exposed to actinic radiation at a first wavelength (532 nm) for activation. Holographic recording at 407 nm was carried out in the non activated storage location of the media as above. The observed diffraction efficiency for 3 multiplexed holograms was 7.6, 10.6 and 16.8 %, respectively, corresponding to a recording sensitivity of 0.97, 1.11 and 1.27 cm/J respectively, that are only diminished compared to the activated location.

[0167] In contrast, in the current case, the holographic recording media exhibited substantially no recording sensitivity to exposure in the material at the recording second wavelength (λ₂) without having firstly forming the activated photosensitizer molecular switch compound by use of a first exposure at a first activation wavelength (X₁). As described in detail above, this high level of selectivity allows for the recording of holograms in a sensitized location in the media, without risk of loss of recording dynamic range in adjacent locations due, e.g., to spillover of recording (e.g. object or reference beam) light at the recording second wavelength (λ₂).

[0168] The activated photosensitizer molecular switch compound was formed by exposure of the recording material to a first wavelength (X₁) using a frequency doubled Nd:YAG laser (Laser Quantum Model Torus 532-400) emitting at λ=532 nm, wherein incident intensity of 9 mW/cm² was directed to about a 1 cm² area in the media. The minimum pumping exposure energy at the activation wavelength λ_\ required to form the activated photosensitizer molecular switch compound was not determined, so an extensive exposure time of 10 minutes was used as a default condition for activation of the photosensitizer molecular switch compound. Evidence that the activated photosensitizer molecular switch compound was formed at the activation wavelength X₁ was based upon separate evaluation of the extent and kinetics of photopolymerization upon exposure of the same photopolymerizable material to a second wavelength λ₂ using the method of Photo Differential Scanning Calorimetry (PDSC), wherein an optical system equipped with a Hg lamp and monochromator is coupled into the calorimeter to provide for illuminating the photopolymerizable material with control of intensity and wavelength (see Waldman et al, J. Imaging Sd. Technol. 41, (5), pp. 497-514, (1997)).

[0169] Co-locational slant fringe plane-wave transmission volume holograms were recorded at the second wavelength, λ₂, in the conventional manner with a Sony Corp SBL single longitudinal mode blue-purple diode laser model emitting at 407 nm using two coherent spatially filtered and collimated laser writing beams directed onto the sample with an interbeam angle of 51.3°. The intensities of the two writing beams at the condition of equal semiangles about the normal were 2.3 and 2.5 mW/cm², and the total incident intensity for recording was 4.85 mW/cm² as measured at the bisecting condition. Nine planar angle multiplexed co- locational plane-wave transmission volume holograms were recorded at the second wavelength, λ₂ = 407 nm, in the area of the media firstly exposed to the activation first wavelength (X₁ = 532 nm), using recording times consistent with recording energies used for recording holograms in STX Aprilis Type E DHD® media of the same thickness for attaining moderately strong (~5% to -30%) diffraction efficiency for a similarly small number of multiplexed holograms. [0170] Reconstruction of the multiplexed plane-wave holograms recorded at λ₂ = 407 nm was carried out directly after recording utilizing the collimated recording beam having intensity of 2.3 mW/cm². Diffraction efficiency data was obtained at angle increments of 0.02° over an angle sweep of +/- 2.0° from the respective recording angles of each hologram using two model 818-SL/CM photodiodes and a model 2835-C dual channel multi-function optical meter from Newport Corporation for measuring the primary diffracted intensity, I¹, and the transmitted non diffracted intensity, I⁰. The measured diffraction efficiency, η_t, was obtained at the peak of the Bragg selectivity profile of the ith recorded hologram in a storage location in the recording material in accordance with

T₇, = IV(I¹ + I⁰)

wherein the measured values of I¹ and I⁰ were determined for each of the angle increments in the angle scan. The diffraction efficiency values were 1.14, 1.45, 2.15, 2.51, 4.37, 11.77, 3.81, 8.51 and 8.36% for multiplexed volume holograms #1- #9, respectively. Recording sensitivity, S, conventionally normalized to the thickness of the recorded hologram, was determined from the value of peak diffraction efficiency value for each volume hologram, η_t, in accordance with

S = (η_ι ⁰⁵/I*t_ι)/T

wherein T is thickness of the recording material, U is the length of the recording time for the zth recording event, and I₁ is the intensity for the recording event of the zth multiplexed hologram. Recording sensitivities were moderately high at 3.25, 3.56, 3.93, 3.51, 3.47, 3.07, 0.73, 0.67 and 0.49 cm/mJ for the co-locationally multiplexed volume holograms #l-#9, respectively. The cumulative grating strength of the in situ activated recording material, V_M, a standard measure of the dynamic range of HRM based on the summation of the grating strengths of each of the recorded volume holograms multiplexed in a location in the media in accordance with

co-locationally multiplexed holograms for v = (πni7)/(λ cosθ)

where λ is the wavelength at which the hologram is recorded or reconstructed, θ is the internal incidence angle of the Reference beam for reconstruction of the recorded hologram, m is the amplitude of the refractive index modulation of the hologram, M is the number of co-locationally multiplexed volume holograms and T is the thickness of the recording material, was 1.86. The value of recording sensitivity for the last hologram recorded in the sequence of nine co-locationally recorded volume holograms indicates that more multiplexed holograms could still be recorded in the same location by using additional exposures to yield still higher values for the attainable dynamic range.

[0171] A second region in the above recording media was exposed to the same sequence of steps described above for a first exposure to the activation first wavelength (X₁ = 532 nm), followed by recording at the second wavelength, λ₂ = 407 nm, in the second area of the media firstly exposed to the activation first wavelength, excepting that a wait time of 17 hours occurred between the exposure at the activation first wavelength and the recording of holograms at the second wavelength. Again, nine planar angle multiplexed co-locational plane-wave transmission volume holograms were recorded at the second wavelength, λ₂ = 407 nm, in the area of the media firstly exposed to the activation first wavelength (X₁ = 532 nm), using two coherent spatially filtered and collimated laser writing beams, wherein the exposure times in the recording schedule were increased to achieve larger value for attainable dynamic range of the activated media. The measured diffraction efficiencies were comparatively higher at 3.20, 3.28, 4.01, 7.43, 29.64, 24.05, 32.61, 33.63 and 31.36% for volume holograms #l-#9, respectively. Recording sensitivities were again moderately high at 2.32, 1.60, 1.26, 1.12, 1.41, 0.90, 0.89, 0.90 and 0.87 cm/mJ for holograms #l-#9, respectively. The value of 3.59 attained for cumulative grating strength for this recording sequence was considerably larger. Further, the recording sensitivity of the last hologram recorded in the multiplexing sequence was still moderately high, indicating more dynamic range could still be attained in the in situ activated media by recording more multiplexed holograms in the activated region and/or further increasing the recording times in the recording schedule.

[0172] Plots of the growth in cumulative grating strength and of the recording sensitivity versus the cumulative recording fluence in mJ/cm² are shown below in FIGs. 11 and 12, respectively, for the nine co-locationally multiplexed planar angle volume holograms recorded in the material at the second wavelength (λ₂) immediately after the in situ activation was carried out at the first wavelength (λ{) and after a wait time of 17 hours after the same activation step before recording at the second wavelength (λ₂). The growth in cumulative grating strength exhibits a linear ramp with increasing cumulative recording energy, and the recording sensitivity declines and then exhibits a fairly flat dependence with further increases in cumulative recording energy, thereby indicating that the recording chemistry of the activated media was not fully consumed during the recording schedule used for the co-locationally multiplexed volume holograms.

[0173] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0174] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0175] All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.

[0176] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0177] While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A polymerizable media, comprising: at least one monomer or oligomer which undergoes polymerization; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength; wherein: the compound is represented by the following structural formula:

the sensitizer is represented by the following structural formula

ring C is a C3-C7 an optionally fluorinated or perfluorinated cycloalkenyl; ring C is an optionally fluorinated or perfluorinated C3-C7 cycloalkyl; X₁ is a linker group that provides for conjugation between Ar₁ and the thienyl group with which X₁ is connected; X₂ is absent or is a linker group that provides for conjugation between Ar₂ and the thienyl group with which X₂ is connected; Ar₁ is a C6-C22 aryl optionally substituted with an electron donating group or electron withdrawing group, or a 5-14-membered heteroaryl optionally substituted with an electron donating group or electron withdrawing group;

Ar₂ is a C6-C22 aryl optionally substituted with an electron donating group or electron withdrawing group; a 5-14-membered heteroaryl optionally substituted with an electron donating group or electron withdrawing group; or -X₂-Ar₂ is an electron donating group or an electron withdrawing group; and

R₃ and R₄ are independently a Cl-C 12 alkyl group, a Cl-Cl 2 alkenyl group, or a C1-C12 alkoxy group.

2. The polymerizable media of Claim 1, wherein each linker group is independently: an ethynyl group; an ethenyl group; a carbonyl group; a group comprising a carbonyl; a cyclic or acyclic sequence of alternating single and double bonds, optionally comprising an O, S, or N atom; a cyclic or acyclic sequence of alternating single and triple bonds, optionally comprising an O, S, or N atom; or a combination of cyclic or acyclic alternating single and double and single and triple bonds, optionally comprising an O, S, or N atom.

3. The polymerizable media of Claim 1, wherein X₁ and X₂ are the same.

4. The polymerizable media of Claim 1, wherein X₁ and X₂ are not the same.

5. The polymerizable media of any one of Claims 1 -4, wherein Ar₁ for each occasion is independently optionally substituted with a group represented by R^y, wherein R^y is an optionally substituted Cl -C 12 alkyl, an optionally substituted C2- C 12 alkenyl, an optionally substituted C2-C12 alkynyl, an optionally substituted C3-C12 cycloalkyl, an optionally substituted C3-C12 cycloalkenyl, an optionally substituted C6-C14 aryl, or an optionally substituted 5-14-membered heteroaryl or is an electron-donating group selected from Cl -C 12 alkoxy, Cl -C 14 dialkylamine, and a C6- C 14 diarylamine, or is an electron- withdrawing group selected from -NO₂, -CF₃, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', and a halogen, wherein R' is -H or a Cl-C 12 alkyl.

6. The polymerizable media of any one of Claims 1 -4, wherein each linker group is independently an ethynyl group or an ethenyl group; Ar₁ is an optionally substituted C6-C22 aryl; and Ar₂ is an optionally substituted C6- C22 aryl.

7. The polymerizable media of Claim 6, wherein Ar₁ is substituted or unsubstituted phenyl, naphthyl, or anthracenyl; and Ar₂ is substituted or unsubstituted phenyl, naphthyl, or anthracenyl.

8. The polymerizable media of any one of Claims 1-7, wherein the groups represented by Ar₁ and Ar₂ are independently unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3- C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14-membered heteroaryl, an optionally substituted Cl -C 12 alkoxy, Cl -C 14 dialkylamine, a C6-C14 diarylamine, -NO₂, -CF₃, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', or a halogen, and further wherein R' is -H or a Cl-Cl 2 alkyl.

9. The polymerizable media of Claim 8, wherein the groups represented by Ar₁ and Ar₂ are independently unsubstituted or substituted with -Si(R₅)₃; Cl- C12 alkyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs)₃, a Cl- C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; or a 5-14- membered heteroaryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; and wherein each R₅ is independently a Cl-C 12 alkyl.

10. The polymerizable media of any one of Claims 1-7, wherein the groups represented by Ar₁ and Ar₂ are independently unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.

11. The polymerizable media of Claim 1 , wherein each linker group is an ethynyl group; and Ar₁ and Ar₂ are anthracen-9-yl or 6-methoxynaphthalen- 2-yl.

12. The polymerizable media of any one of Claims 1-3, wherein each linker group is thienyl.

13. The polymerizable media of Claim 4, wherein X₁ is phenyl or 5-6 membered heteroaryl and X₂ is absent, wherein the group represented by X₁ is optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl-

C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.

14. The polymerizable media of Claim 13, wherein X₁ is thienyl optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl -C 12 haloalkoxy or cyano.

15. The polymerizable media of Claims 13 or 14, wherein Ar₁ is optionally substituted phenyl or optionally substituted thienyl; and Ar₂ is optionally substituted phenyl.

16. The polymerizable media of Claim 15, wherein Ar₁ is optionally substituted thienyl.

17. The polymerizable media of any one of Claims 13-16, wherein the groups represented by Ar₁ and Ar₂ are independently unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3- C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14-membered heteroaryl, an optionally substituted Cl -C 12 alkoxy, Cl -C 14 dialkyl amine, a C6-C14 diarylamine, -NO₂, -CF₃, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', or a halogen, and further wherein R' is -H or a Cl-Cl 2 alkyl.

18. The polymerizable media of any one of Claims 13-16, wherein the groups represented by Ar₁ and Ar₂ are independently unsubstituted or substituted with -Si(R₅ )₃; C1-C12 alkyl group, optionally substituted with -Si(R₅)₃, a Cl -C 12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with - Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; a 5- 14-membered heteroaryl group, optionally substituted with -Si(Rs)₃, a Cl-

C 12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; and wherein each R₅ is independently a Cl-Cl 2 alkyl.

19. The polymerizable media of any one of Claims 13-16, wherein the groups represented by Ar₁ and Ar₂ are independently unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, C1-C12 haloalkyl, C1-C12 haloalkoxy or cyano.

20. The polymerizable media of Claim 15 or 16, wherein the group represented by Ar₁ is optionally substituted with Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl and Cl -C 12 haloalkyl and the group represented by Ar₂ is optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl -C 12 haloalkoxy or cyano.

21. The polymerizable media of Claim 1 , wherein -X₂-Ar₂ is an electron withdrawing group.

22. The polymerizable media of Claim 1 wherein -X₂-Ar₂ is halogen, Cl -C 12 alkyl or Cl -C 12 haloalkyl.

23. The polymerizable media of any one of Claims 21 -22, wherein X₁ is phenyl or 5-6 membered heteroaryl and wherein the group represented by X₁ is optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl- C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.

24. The polymerizable media of Claim 23, wherein X₁ is thienyl optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, C1-C12 haloalkenyl, C1-C12 alkoxy, C1-C12 haloalkoxy or cyano.

25. The polymerizable media of Claims 23 or 24, wherein Ar₁ is an optionally substituted phenyl or thienyl.

26. The polymerizable media of Claim 25, wherein Ar₁ is an optionally substituted thienyl.

27. The polymerizable media of any one of Claims 23-26, wherein the group represented by Ar₁ is unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3-C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14-membered heteroaryl, an optionally substituted Cl -C 12 alkoxy, Cl -C 14 dialkylamine, a C6-C14 diarylamine, -NO₂, -CF₃, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO₃R', or a halogen, and further wherein R' is -H or a Cl-C 12 alkyl.

28. The polymerizable media of any one of Claims 23-26, wherein the group represented by Ar₁ is unsubstituted or substituted with -Si(Rs)₃; C1-C12 alkyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(R₅ )₃, a Cl- C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; or a 5-14- membered heteroaryl group, optionally substituted with -Si(Rs)₃, a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; and wherein each R₅ is independently a Cl-C 12 alkyl.

29. The polymerizable media of any one of Claims 23-26, wherein the group represented by Ar₁ is unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.

30. The polymerizable media of Claim 26, wherein the optionally substituted thienyl group represented by Ar₁ is optionally substituted with Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 haloalkyl, or a thineyl group.

31. The polymerizable media of any one of Claims 1 -4, wherein Ar₁ is thienyl optionally substituted with F, Cl, Br, I, CN, Cl -C 12 alkyl, or haloalkyl.

32. The polymerizable media of any one of Claims 1 -7, wherein Ar₁ is a hexylthienyl group, a phenyl group, a methoxyphenyl group, a naphthyl group, an anthracenyl group, a phenylanthracenyl group, a methoxyanthracenyl group, or methylthienyl group; and Ar₂ is a hexylthienyl group, a naphthyl group, an anthracenyl group, a phenylanthracenyl group, a methoxyanthracenyl group, methylthienyl group, a trifluoromethylphenyl group, a bis-trifluoromethylphenyl group, or Br.

33. The polymerizable media of any one of Claims 1, 2, 4, 5, 8, 9, 10, 31, or 32, wherein X₁ is thienyl and X₂ is ethynyl.

34. The polymerizable media of any one of Claims 1-33, wherein ring C is a perfluorocyclopentene and ring C is a perfluorocyclopentane.

35. The polymerizable media of Claim 1 , wherein the compound is:

36. The polymerizable media of any one of Claims 1-35, further comprising a binder, wherein chemical segregation or spatial separation of the binder from the polymerized monomer or oligomer produces refractive index modulation within the polymerizable media.

37. The polymerizable media of Claims 36, wherein the produced refractive index modulation forms a hologram.

38. The polymerizable media of any one of Claims 1-37, wherein actinic radiation of the first wavelength is visible light.

39. The polymerizable media of any one of Claims 1-37, wherein actinic radiation of the first wavelength is UV light.

40. The polymerizable media of any one of Claims 1-37, wherein actinic radiation of the first wavelength is near infrared radiation or infrared radiation.

41. The polymerizable media of any one of Claims 1-40, wherein the initiator is a photoacid generator (PAG), and wherein the PAG produces acid in combination with the sensitizer.

42. The polymerizable media of Claim 41 , wherein the initiator is a sulfonium, sulfoxonium, iodonium, diazonium, or phosphonium salt.

43. The polymerizable media of any one of Claims 1 -42, wherein the at least one monomer or oligomer undergoes cationic polymerization.

44. The polymerizable media of any one of Claims 1-43, wherein the monomer or oligomer which is capable of undergoing polymerization contains one or more epoxide, oxetane, cyclic ether, 1 -alkenyl ether, unsaturated hydrocarbon, lactone, cyclic ester, lactam, cyclic carbonate, cyclic acetal, aldehyde, cyclic sulfide, cyclosiloxane, cyclotriphosphazene, or polyol functional groups, or a combination of any two or more thereof.

45. The polymerizable media of Claim 44, wherein the monomer is an epoxide monomer that comprises one or more cyclohexene oxide groups.

46. The polymerizable media of Claim 45, wherein the epoxide monomer is a siloxane, siloxysilane comprising two or more cyclohexene oxide groups, or a polyfunctional siloxane comprising three or more cyclohexene oxide groups.

47. The polymerizable media of Claim 1, wherein the initiator is a free radical generator that produces free radicals in combination with the sensitizer.

48. The polymerizable media of Claim 47, wherein the at least one monomer or oligomer undergoes free radical polymerization.

49. The polymerizable media of any one of Claims 1-48 further comprising a second monomer or oligomer which is capable of undergoing polymerization.

50. The polymerizable media of Claim 47, wherein the produced free radicals initiate free radical polymerization reactions.

51. The polymerizable media of any one of Claims 1-50, wherein the sensitizer is a linear absorbing dye.

52. The polymerizable media of any one of Claims 1-50, wherein the sensitizer is a non-linear-absorbing dye.

53. The polymerizable media of any one of Claims 1 -52, wherein the amount of sensitizer is controlled by the intensity of the actinic radiation of the first wavelength or by the duration of the exposure of the compound to the actinic radiation of the first wavelength.

54. The polymerizable media of any one of Claims 1-53, wherein the actinic radiation of the first wavelength is used as a source of light for generating a servo signal from the media.

55. A method of polymerizing a polymerizable media according to any one of Claims 1-54, comprising:

(a) exposing a first location in the polymerizable media to actinic radiation of the first wavelength, thereby forming a sensitizer from the compound; and

(b) exposing the first location in the polymerizable media to actinic radiation of the second wavelength, thereby initiating polymerization of the at least one monomer or oligomer.

56. The method of Claim 55, wherein steps (a) and (b) are repeated, and wherein, for each repetition of step (a), step (b) is repeated one or more times.

57. The method of Claim 55, wherein steps (a) and (b) are performed at a second location in the polymerizable media.

58. The method of Claim 57, wherein the second location is abutting or at least partially overlapping the first location.

59. The method of Claim 57, wherein the second location is neither abutting nor overlapping the first location.

60. The method of Claim 55, wherein steps (a) and (b) occur substantially at the same time.

61. The method of Claim 55, wherein: during step (a), a portion of the polymerizable media outside of the first location is not exposed to the actinic radiation of the first wavelength, and wherein this portion of the polymerizable media is inactive to the actinic radiation of the second wavelength.

62. The method of Claim 61, wherein during step (b) a portion of the actinic radiation of the second wavelength is incident on the inactive portion of the polymerizable media, and wherein substantially no polymerization is initiated in the inactive portion of the polymerizable media in response to the actinic radiation of the second wavelength.

63. The method of Claim 61 or 62, wherein the inactive portion of the polymerizable media abuts the first location.

64. A method of recording a hologram in a holographic recording media (HRM) that comprises the polymerizable media according to any one of Claims 1- 54, wherein the media additionally comprises a binder, the method comprising:

(a) exposing a first storage location in the holographic recording media to a beam of actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing actinic radiation of a second wavelength; and

(b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location, thereby forming an interference pattern in the HRM at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer and thereby recording the interference pattern as a hologram within the HRM at the first storage location.

65. The method of Claim 64, wherein the interference pattern recorded as a hologram in the HRM at the first storage location is a volume hologram recorded substantially through the thickness of the HRM or is a volume hologram recorded partially through the thickness of the HRM.

66. The method of Claim 64 or 65, wherein step (b) is repeated one or more times at the first storage location thereby recording multiplexed holograms in the HRM at the first storage location.

67. The method of Claim 64 or 65, wherein steps (a) and (b) are repeated at the first storage location, and wherein, for each repetition of step (a), step (b) is repeated one or more times thereby recording multiplexed holograms in the HRM at the first storage location.

68. The method of Claim 64 or 65, wherein steps (a) and (b) are performed at a second storage location in the holographic recording media.

69. The method of Claim 64 or 65, wherein step (b) is repeated one or more times in the second storage location thereby recording multiplexed holograms in the HRM at the second storage location.

70. The method of Claim 68, wherein the second storage location is abutting or at least partially overlapping the first storage location.

71. The method of Claim 68, wherein the second storage location is neither abutting nor overlapping the first storage location.

72. The method of Claim 64, wherein steps (a) and (b) occur substantially at the same time.

73. The method of Claim 64, wherein the multiplexed holograms are recorded in the HRM at the first storage location using a multiplexing method selected from planar angle multiplexing, shift-multiplexing including co-linear shift multiplexing, phase-multiplexing, phase encoded multiplexing, azimuthally multiplexing, out-of-plane tilt-multiplexing, and polytopic spatial multiplexing.

74. The method of Claim 64, wherein the multiplexed holograms are recorded in the HRM at the first storage location using two or more multiplexing methods.

75. The method of Claim 74, wherein the multiplexed holograms recorded in the HRM at the first storage location using two or more multiplexing methods, are multiplexed with at least one multiplexing method selected from planar angle multiplexing, shift-multiplexing including co-linear shift multiplexing, phase-multiplexing, phase encoded multiplexing, azimuthally multiplexing, out-of-plane tilt-multiplexing, and polytopic spatial multiplexing.

76. The method of Claim 64, wherein to the beam of actinic radiation of the first wavelength, the reference beam or the object beam are produced by a source of actinic radiation that is a continuous emitting source or a pulsed source.

77. The method of Claim 76, wherein the source of actinic radiation is a diode laser, and further, wherein the diode laser optionally comprises an external cavity.

78. The method of Claim 76, wherein the source of actinic radiation is a light emitting diode.

79. The method of Claim 64, wherein the beam of actinic radiation of the first wavelength, the reference beam or the object beam each independently has a Gaussian intensity distribution at the first storage location in the HRM.

80. The method of Claim 64, wherein the beam of actinic radiation of the first wavelength, the reference beam or the object beam each independently has a truncated Gaussian intensity distribution at the first location in the HRM, wherein the minimum diameter of the truncated Gaussian intensity distribution is less than or equal to the diameter of said beam, dy_e2, measured at the l/e intensity point.

81. The method of Claim 64, wherein exposing the first location to the beam of actinic radiation of the first wavelength or the reference beam or the object beam exposes a volume element of the HRM having a cross-sectional area that changes as a function of depth through the HRM.

82. The method of Claim 64, wherein of the beam of actinic radiation of the first wavelength, the reference beam, or the object beam is each independently generated by a tunable source.

83. The method of Claim 64, wherein actinic radiation of the first wavelength is visible light.

84. The method of Claim 64, wherein actinic radiation of the first wavelength is UV light.

85. The method of Claim 64, wherein actinic radiation of the first wavelength is near infrared or infrared radiation.

86. The method of Claim 64, wherein the hologram is a binary data page volume hologram.

87. The method of Claim 86, wherein the binary data page volume hologram is recorded with an object beam that is amplitude modulated or phase modulated.

88. The method of Claim 64, wherein the volume hologram is a micrograting recorded in a portion of a volume in the HRM at the first storage location, wherein the micrograting can be recorded in a portion of the volume in the thickness direction of the HRM at the first storage location or in portion of the volume in the lateral direction at the first storage location, or combinations thereof.

89. The method of Claim 88, wherein one or more microgratings are recorded in the portion of the volume in the HRM at the first storage location by repeating step (b) at the first storage location, thereby recording multiplexed microgratings that overlap at least in part in the said portion of the volume of the first storage location.

90. The method Claim of 88, wherein the multiplexed microgratings are recorded with two or more different wavelengths or two or more different phases or combinations thereof.

91. The method of Claim 64, wherein the beam of actinic radiation of the first wavelength is a collimated beam.

92. The method of Claim 64, further including a step (c) of reading the recorded hologram after recording the hologram at the first storage location, wherein the reading step confirms the recording of the hologram at the first storage location.

93. The method of Claim 64, wherein: during step (a), a portion of the holographic recording media outside of the first location is not exposed to the actinic radiation of the first wavelength, and wherein this portion of the holographic recording media is inactive to the actinic radiation of the second wavelength.

94. The method of Claim 64, wherein during step (b) a portion of at least one of the reference and object beams of coherent light of the second wavelength is incident on the portion of the holographic recording media which is inactive to actinic radiation of the second wavelength, and wherein substantially no preconsumption of dynamic range of the holographic recording media occurs in the inactive portion in response to the at least one of the reference and object beams of coherent light at the second wavelength.

95. The method of Claim 94, wherein the inactive portion of the holographic recording media abuts the first location or is at least partially overlapping the first location or is separated from the first location.

96. The method of Claim 94, wherein steps (a) and (b) are repeated at a second storage location in the holographic recording media, and wherein the second location includes at least part of the inactive portion of the holographic recording media.

97. A method of recording a micrograting hologram in a holographic recording media (HRM) that comprises the polymerizable media according to any one of Claims 1-54, wherein the polymerizable media additionally comprises a binder, the method comprising

(a) exposing a first storage location in the holographic recording media to actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing electromagnetic radiation of a second wavelength, said first storage location being located in a portion of the depth of the HRM; and

(b) directing a reference beam of the second wavelength and an object beam of the second wavelength at the first storage location, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, and initiating polymerization of the at least one monomer or oligomer in the first storage location and thereby recording the interference pattern as a micrograting hologram within said first storage location.

98. The method of Claim 97, wherein: during step (a), a portion of the HRM outside of the first location is substantially unexposed to the actinic radiation of the first wavelength, and wherein this portion of the HRM is substantially inactive to the actinic radiation of the second wavelength.

99. The method of Claim 98, wherein during step (b) a portion of at least one of the reference and object beams of coherent light of the second wavelength is incident on the portion of the HRM which is inactive to actinic radiation of the second wavelength, and wherein substantially no preconsumption of dynamic range of the HRM occurs in the inactive portion in response to the at least one of the reference and object beams of coherent light at the second wavelength.

100. The method of Claim 99, wherein the inactive portion of the HRM abuts the first location or is separated from the first location.

101. The method of Claim 99, wherein steps (a) and (b) are repeated at a second storage location in the HRM, and wherein the second location includes at least part of the inactive portion of the HRM.

102. The method of Claim 101, further including a step (c) of reading the recorded micrograting hologram after recording the micrograting hologram at the first storage location, wherein the reading step confirms the recording of the micrograting hologram at the first storage location.

103. A method of recording a hologram in a holographic recording media (HRM) that comprises the polymerizable media according to any one of Claims 1- 54, wherein, the polymerizable media additionally comprises a binder, the method comprising

(a) exposing a first storage location in the HRM to a beam of actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing electromagnetic radiation of a second wavelength; and

(b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location in the HRM, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer and recording the interference pattern therefrom as a hologram within said first storage location, wherein the beam of actinic radiation of the first wavelength, the reference beam, or the object beam is each independently generated by a tunable source.

104. The method of Claim 101, wherein: during step (a), a portion of the HRM outside of the first location is not exposed to the actinic radiation of the first wavelength, and wherein this portion of the HRM is inactive to the actinic radiation of the second wavelength.

105. The method of Claim 104, wherein during step (b) a portion of at least one of the reference and object beams of coherent light of the second wavelength is incident on the portion of the HRM which is inactive to actinic radiation of the second wavelength, and wherein substantially no preconsumption of dynamic range of the HRM occurs in the inactive portion in response to the at least one of the reference and object beams of coherent light at the second wavelength.

106. The method of Claim 105, wherein the inactive portion of the HRM abuts the first location or is separated from the first location.

107. The method of Claim 105, wherein steps (a) and (b) are repeated at a second storage location in the HRM, and wherein the second location includes at least part of the inactive portion of the HRM.

108. An optical article, comprising: two or more substrates; and a holographic recording medium (HRM) therebetween, said HRM comprising the polymerizable media according to any one of

Claims 1-54.