JPH02287518A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain the quadratic org. nonlinear optical material which as large nonlinear optical characteristics and allows easy film formation and molding and with which the central symmetricalness is hardly obtainable by forming the material of a pi-conjugation high-polymer compd. which is obtd. from a precursor soluble in a solvent and is expressed by specific formula. CONSTITUTION:The quadratic org. nonlinear optical material having high performance is obtd. by using the precursor soluble in the solvent, obtaining the precursor thin film by a simple process for producing the thin film and subjecting this precursor thin film to a heat treatment. Namely, the pi-conjugation high- polymer precursor film is produced from the pi-conjugation high-polymer precursor soluble in the solvent and thereafter, this high-polymer precursor film is changed to the pi-conjugation high-polymer film and, therefore, the process for producing the element is extremely simplified. The pi-conjugation high polymer to be used is obtd. from the precursor of the pi-conjugation high polymer soluble in the solvent and is expressed by the formula. Such pi-conjugation high polymer has excellent characteristics, such as high nonlinear optical constant and high SHG activity.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to novel organic nonlinear optical materials.

[Prior art/problems to be solved by the invention] Nonlinear optical materials can generate second harmonics (hereinafter referred to as SHO),
It is an optical material used in wavelength conversion such as third harmonic generation (hereinafter referred to as THG), and active optical devices such as optical switches and phase conjugate wave generation, and will play a core role in the future optical information processing field. It is expected to be a material that plays a role in Among these, there is a strong desire for an SHG element that can efficiently halve the oscillation wavelength of a semiconductor laser, which is difficult to oscillate at a short wavelength of about 700 nm or less due to band gap limitations. This demand is particularly noticeable in the field of optical disk devices, where by halving the oscillation wavelength, the condensing area can be reduced to 1/4, and as a result, the recording density can be quadrupled.

The most widely used nonlinear optical material has been inorganic ferroelectric crystals such as KDP. but,
These inorganic materials have the disadvantage of having small nonlinear optical constants. In particular, since the efficiency for second harmonic generation is proportional to the square of the incident optical power, inorganic nonlinear optical materials are often used in industrial fields that require the use of relatively low-power light sources such as semiconductor laser light. The reality is that it cannot be used.

Against this background, organic materials are attracting attention as materials that can generate second harmonics with high efficiency (D.J. Williams
laas), A.S. Symposium Series (^C8Symp, Ser.), Vow.

233, Nonlinear Optical Properties of Organic and Bolimeric Materials (Non11near Optical Pro
pearlsof Organic and Pol
ymeric Materials) J (1983))
. However, among these organic materials, low-molecular organic nonlinear optical materials have problems in terms of stability and properties. In order to obtain large nonlinear optical constants, it is thought that polymeric materials with long π-conjugation lengths are desirable;
Many polymer compounds with a long conjugation length (hereinafter referred to as π-conjugated polymers) are insoluble and infusible, and have the disadvantage of being extremely poor in processability.

On the other hand, in organic nonlinear optical materials, there are two main factors that govern their nonlinear optical constants: first, one molecule in the case of a low-molecular compound, and the repeating unit in the case of a polymer material. is the molecular hyperpolarizability of the monomer units, and the second is their arrangement. When using a thin film as a second-order nonlinear optical material for second-order harmonic generation, there is no need to consider bulk phase matching due to birefringence, etc., and the molecules are arranged so that all the molecular hyperpolarizabilities strengthen each other. This is desirable. Therefore, it is necessary to align the molecules in the normal direction or in one direction within the plane. (In any case, these highly oriented materials can be used in a variety of ways, including transmission type and waveguide type.) However, conventional and simple thin film formation methods, such as spin cording, casting, and dipping, Thin films fabricated using methods such as method, barcode method, roll coating method, etc. are in an amorphous state with no order, and second harmonic generation requires a structure without center symmetry. It could not be used as a second-order nonlinear optical material for optical mixing, parametric oscillation, electro-optic effects, etc.

In addition, as a method for obtaining such highly oriented organic thin films,
Although the Langmuir-Blodgett method (LB method) and the organic molecular beam epitaxy method (OMBE method) have already been proposed, these methods are currently very complicated and complicated.

As described above, conventionally, there has been no method of forming a thin film without central symmetry using a simple thin film forming method of a π-conjugated polymer.

[Means for Solving the Problems] The present invention solves the above-mentioned conventional problems, has large nonlinear optical characteristics, is easy to form and mold, and has central symmetry. This work was done to provide a novel second-order organic nonlinear optical material consisting of an active π-conjugated polymer.

In other words, in the past, many π-conjugated polymers were insoluble and infusible, so they lacked process controllability. The purpose is to obtain a high-performance second-order organic nonlinear optical material by heat treatment of a precursor thin film, and the general formula CI) obtained from a solvent-soluble precursor is: (wherein R1 and R2 are each ~ The present invention relates to a second-order organic nonlinear optical material comprising a π-conjugated polymer compound represented by an L alkyl group or an alkoxy group, where n is an integer.

[Function] In the present invention, a π-conjugated polymer precursor film is prepared from a solvent-soluble π-conjugated polymer precursor, and then this polymer precursor film is formed into a π-conjugated polymer membrane. As a result, the device fabrication process becomes significantly easier, and a highly efficient second-order nonlinear optical material thin film can be obtained.

[Implementation flJ] The π-conjugated polymer used in the present invention has a precursor thereof that is soluble in a solvent, and the π-conjugated polymer obtained from such a precursor is It is represented by the general formula (I): RI R2 (wherein R1 and R2 each represent an -H1 alkyl group or an alkoxy group, and n represents an integer). Such π-conjugated polymers have excellent properties such as high nonlinear optical constants and high SHG activity.

Specific examples of the alkyl group that is a type of R1 and R2 in general formula (1) include methyl group, ethyl group, n
-propyl group, 1so-propyl group, n-butyl group, 1
so-butyl group, t-butyl group, n-pentyl group, n-
Examples include hexyl group, n-heptyl group, n-octyl group, n-nonyl group, and n-decyl group. Further, specific examples of other types of alkoxy groups include methoxy group, ethoxy group, n-propoxy group, 1so-propoxy group, n-butoxy group, 1so-butoxy group, t-
Butoxy group, n-pentyloxy group, n-hexyloxy group, n-hebutyloxy group, n-octyloxy group,
Examples include n-nonyloxy group and n-decyloxy group. Among the compounds represented by the general formula (11), R1
A compound in which R2 is -H is preferred because it facilitates the synthesis of a π-conjugated polymer precursor.

Further, n in the general formula (11) is preferably 5 or more from the viewpoint of expressing a second-order nonlinear optical effect.

The n units constituting the π-conjugated polymer represented by the general formula (1) do not need to be the same, and two or more solvent-soluble precursors may be used in combination to form the π-conjugated polymer. May be manufactured.

The π-conjugated polymer represented by the general formula (1) does not have any particular problem even if any group is attached to the end of the molecule.

The solvent refers to various organic solvents such as dimethylformamide, dimethylacetamide, chloroform, tetrahydrofuran, dimethyl sulfoxide, and dioxane, water, and mixtures thereof.

Next, the general ceremony! The precursor of the π-conjugated polymer represented by 1) will be explained by citing as a representative example a precursor of the π-conjugated polymer in which R1 and R2 in the general formula (11) are both -H.

π in which R1 and R2 in general formula (1) are both -H
As the precursor of the conjugated polymer, those represented by the general formula (I): (wherein, R3 is a hydrocarbon group having 1 to 10 carbon atoms, and m is an integer) are preferable from the viewpoint of storage stability. .

Any hydrocarbon group having 1 to 10 carbon atoms can be used as R3, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, 2-ethylhexyl group, cyclohexyl group, etc. However, from the viewpoint of precursor stability, coating properties, and ease of conversion into a π-conjugated polymer, a hydrocarbon group having 1 to 6 carbon atoms, particularly a methyl group and an ethyl group, is preferred. The m is preferably larger from the viewpoint of coating properties, and is 5 or more,
More preferably, it is 20 to 50,000.

For example, a precursor having a molecular weight that cannot be dialyzed by a dialysis membrane having a molecular weight cutoff of 3,500 or more can be effectively used.

There are no particular limitations on the synthesis method of the polymer precursor used in the present invention, but for example, in the case of the polymer precursor represented by general formula (II), the polymer precursor obtained by the sulfonium salt decomposition method described below is , preferred from the viewpoint of stability.

The sulfonium salt decomposition method is performed using, for example, the general formula % formula % [
): (wherein R' and R5 are each a hydrocarbon group having 1 to 1 o carbon atoms, and A- represents a counter ion) 2,5
- This is a method in which a chenylene dimethylsulfonium salt is subjected to condensation polymerization in a solvent, and then the side chain is converted into an alkoxy group. R4 and R5 in the general formula circle have 1 to 10 carbon atoms.
Any hydrocarbon group can be used, such as methyl group, ethyl group, propyl group, isopropyl group,
Examples include n-butyl group, 2-ethylhexyl group, cyclohexyl group, benzyl group, etc., but from the viewpoint of ease of synthesis, stability, and ease of polymerization reaction, hydrocarbon groups having 1 to 6 carbon atoms, especially methyl group are preferred. and ethyl group are preferred. There are no particular restrictions on the counter ion A-, but examples include halogen ions, hydroxide ions, boron tetrafluoride ions, perchlorate ions, carboxylate ions, and sulfonate ions. From the viewpoint of stability and ease of polymerization reaction, halogen ions such as chloride ions and bromine ions, and hydroxide ions are preferred.

As the solvent for the condensation polymerization, for example, water or alcohol (alcohol consisting of a hydrocarbon group having 1 to 10 carbon atoms, such as methyl alcohol, ethyl alcohol,
Butyl alcohol, etc.) alone or a mixed solvent containing water and alcohol can be used. The reaction solution is preferably an alkaline solution since polymerization proceeds with alkali, and the alkaline solution is preferably a strongly basic solution with a pH of 11 or higher. Examples of the alkali that can be used include sodium hydroxide, potassium hydroxide, calcium hydroxide, quaternary ammonium salt hydroxide, sulfonium salt hydroxide, strong basic ion exchange resin (011 type), etc. In terms of reaction rate and reaction yield, sodium hydroxide, potassium hydroxide, quaternary ammonium salt hydroxides and strongly basic ion exchange resins are particularly preferred.

Regarding the reaction conditions for the condensation polymerization, since sulfonium salts are unstable under conditions such as heat, light, especially ultraviolet rays, and strong basicity, desulfonium salts gradually occur after condensation polymerization, resulting in conversion to alkoxy groups. cannot be carried out effectively (because of this, the condensation polymerization reaction is carried out at a relatively low temperature, i.e. 25°C).
Hereinafter, it is preferable to carry out the reaction at a temperature of 5°C or lower, particularly -1H°C or lower. The reaction time may be adjusted as appropriate depending on the polymerization temperature and is not particularly limited, but is usually in the range of 1° minute to 50 hours.

According to the sulfonium salt decomposition method, after polymerization, the precursor of the π-conjugated polymer is first produced as a sulfonium salt and a molecular electrolyte (polymer sulfonium salt), but then the sulfonium salt side chain is converted to alcohol (R30H) in the solution. ), and the alkoxy group of the alcohol (corresponding to OR3 in general formula (II)) becomes a side chain. Therefore, the solvent used needs to contain an alcohol corresponding to the above-mentioned -OR group.

These alcohols may be used alone or in combination with other solvents. The solvent used for mixing is not particularly limited as long as it is soluble in alcohol, but water is preferred from the practical standpoint of ease of mixing and ease of reaction. Regarding the mixing ratio when using a mixed solvent, it is sufficient as long as alcohol is present, but a solvent containing 5% by weight or more of alcohol is preferable.

In the reaction of substituting a sulfonium side chain with an alkoxy group, the sulfonium side chain can be effectively substituted with an alkoxy group by raising the temperature higher than the condensation polymerization temperature in a solvent containing alcohol after condensation polymerization. When the polymerization solvent contains the above-mentioned alcohol, an alkoxy group substitution reaction can be carried out subsequent to the polymerization. On the other hand, if the polymerization solvent is water or the like and does not contain alcohol, the same procedure can be carried out by mixing alcohol after polymerization. In the substitution reaction for an alkoxy group, the reaction temperature is preferably 0 to 50"C from the viewpoint of reaction rate, and more preferably 0 to 25"C. As the reaction progresses, it precipitates. Therefore, it is effective to carry out the reaction until sufficient precipitation occurs, and the reaction time is preferably 15 minutes or more, but from the viewpoint of yield, 1 hour or more is preferable. The π-conjugated polymer precursor having an alkoxy group in the side chain thus obtained is separated by filtering the precipitated product.

In order to obtain a π-conjugated polymer precursor with good coating properties, it is preferable that the molecular weight is sufficiently large. It can be effectively used.

The π-conjugated polymer precursor having an M-removal group such as an alkoxy group in a side chain has excellent solubility and is soluble in many organic solvents. Examples of these organic solvents include dimethylformamide, dimethylacetamide, dimethylsulfoxide, dioxane, chloroform, and tetrahydrofuran.

Next, a method for obtaining a π-conjugated polymer represented by the general formula +1) from the aforementioned precursor will be explained.

There are no particular limitations on the method, but for example, a π-conjugated polymer precursor solution with a concentration of about 0.1 to 10% by weight may be used to perform spin coding, casting, dipping, barcoding, roll coating, etc. After forming a film by a method etc.,
A π-conjugated polymer precursor thin film is obtained by evaporating the solvent, and the π-conjugated polymer precursor thin film is heated to form a π-conjugated polymer precursor thin film.

There are no particular restrictions on the heating conditions, but in practice it is 200 to 3
It is preferable to carry out the reaction at 00° C. under an atmosphere of an inert gas such as nitrogen or argon. Of course, it is possible to turn a π-conjugated polymer precursor thin film into a π-conjugated polymer film even when heated at 200° C. or lower. The heating time is preferably 0.5 to 5 hours, more preferably 1 to 3 hours. Furthermore, when heated in an inert gas atmosphere containing a protonic acid such as HCg or HBr, the conversion from a π-conjugated polymer precursor thin film to a π-conjugated polymer thin film often proceeds smoothly. Note that instead of heating, concentrated hydrochloric acid,
The precursor can also be converted into a π-conjugated polymer by immersing it in a strong acid such as concentrated sulfuric acid or by irradiating it with light.

The resulting thin film is usually 4.
Preferably, the thickness is between 00 and 20,000 people.

π expressed by the general formula (1) obtained by the above method
- Conjugated polymer thin films are useful as nonlinear optical materials
- Not only is it a conjugated polymer, but the detailed cause is unknown, but it is a thin film that lacks central symmetry, which is essential for second harmonic generation.

As described above, according to the present invention, an organic thin film in which π-conjugated polymers having a large molecular hyperpolarizability necessary for a second-order nonlinear optical material are oriented in a highly ordered manner can be produced using a simple method such as a spinner method. It has the characteristic of being able to wander.

Normally, organic thin films obtained by such thin film formation methods do not exhibit large second-order nonlinear optical properties, and the detailed reason why highly oriented organic thin films can be obtained in the case of the present invention is unknown at present. , by its heat treatment using the precursor π
-It is thought that this has something to do with the fact that conjugated polymers are used. That is, during film formation, π from the interaction inside the material or the interaction between the material and the substrate or from the precursor
- It is thought that due to some action during the conversion process by heat treatment into a conjugated polymer, the material form retains its orientation and is able to move through the thin film of a second-order nonlinear optical material that is SHG active and has no central symmetry. It will be done.

Hereinafter, the present invention will be explained using specific examples, but the present invention is not limited thereto.

Example 1 1 g of 2.5-thennylene-bis(methylenedimethylsulfonium chloride) O was dissolved in 200 ml of a mixed solvent of ion-exchanged water and methanol (volume ratio 1:3), and then 20% tetramethylammonium hydroxide was added. A mixed solution of 9.1 g of methanol solution and 80 ml of methanol was added dropwise at -30°C over 30 minutes.
Stirring was continued for a minute. This reaction solution was quickly put into a dialysis membrane (Cellotube 01 molecular weight fractionation gooo, manufactured by Union Carbide), and the water-methanol mixed solvent cooled to 0°C (
When the membrane was soaked in a solution (1:1) and subjected to dialysis treatment for one day, a yellow precipitate was formed within the dialysis membrane.

This precipitate was dissolved in chloroform, cast, and dried under a nitrogen stream to obtain a yellow precursor film. The infrared absorption spectrum of the film is 1100 cm.
Since absorption of an ether bond was observed at -', it was confirmed that the precursor polymer had a methoxy group in the side chain.

(wherein n is about 1800) poly(2,5-
chenylene vinylene) precursor was obtained.

The temperature of the glass substrate and the ambient temperature were set at about 60°C, and a solution of about 2% by weight dimethylformamide (DMF) of poly(2,5-thennylenevinylene) precursor was applied onto the glass substrate by spin coating. and dried to form a precursor film. At this time, the rotation speed of the spinner was 2000 revolutions per minute. The thickness of the obtained precursor film was approximately 800 mm.

Next, the glass substrate coated with the poly(2,5-chenylene vinylene) precursor film was heated in an infrared imaging furnace.
The mixture was heated at 270° C. under a nitrogen stream for about 2 hours.

As a result, the color of the precursor film changed from pale yellow to brown. By the above heat treatment, the poly(2,5-thennylene vinylene) precursor film changes to a poly(2,5-thhenylene vinylene) (hereinafter referred to as PTV) film, and accordingly, in the infrared absorption spectrum,
Absorption based on C-C appeared at 90ca+-'.

The SHG characteristics of the obtained PTV film were determined using the manufacturer's fringe method. The Maker fringe method is a method used to evaluate the nonlinear optical constant χ('2J) of a thin film material, and determines its χ(21) by comparing it with a standard sample (quartz single crystal). rotate the sample, change the polarization of the incident light and the outgoing S)! light to P-polarized or S!
Depending on the combination of polarization settings, each component of the nonlinear optical constant tensor can be determined.

Figure 1 shows the experimental system used in this measurement. YAG laser (
1) The laser beam of wavelength t and oaum emitted from the polarizer ('
After becoming linearly polarized light by 2I, it is focused by a lens (3), and the thin film sample (5) is placed on a rotating stage (4).
is irradiated. A second harmonic is generated in the sample, and the incident light is removed by a filter (6) and adjusted to an appropriate amount of light.Only the SH light of the desired polarization is extracted by a polarizer (sword), and a photomultiplier tube (8) It is detected at (9) in the figure.
) is a boxcar integrator, and (g)) is a controller.

5) IG manufacturer fringe of the PTV film obtained in Figure 2 is shown (incident light: P polarized light, output SH light: P polarized light).

The horizontal axis is the rotation angle of the sample, and the vertical axis is the SH generated in the sample.
G light intensity. As shown in FIG. 2, maker fringes peculiar to the thin film sample were observed, indicating that the PTV spin code film maintained vertical alignment with respect to the substrate.

Although the cause of this is not clear at present, it is thought to be due to interaction within the material or between the material and the substrate.

Furthermore, the nonlinear optical constants of the obtained PVT film are shown in Table 1.

Example 2 A glass substrate coated with a PTV precursor film obtained in the same manner as in Example 1 was heated in an infrared image furnace at 240° C. under a nitrogen stream for about 2 hours. Table 1 shows the nonlinear optical constants of the obtained PTV film.

Example 3 A glass substrate coated with a PTV precursor film obtained in the same manner as in Example 1 was heated in an infrared image furnace at 210° C. under a nitrogen stream for about 2 hours. Table 1 shows the nonlinear optical constants of the obtained PTV film.

Example 4 4 g of 3-methoxy-2,5-chenylene-bis(methylenedimethylsulfonium bromide) Il was added to 200 ml of a mixed solvent of ion-exchanged water and methanol (volume ratio 1:1).
After the mixture was dissolved in 20 ml of 1N NaOH and 80 ml of methanol, a mixed solution of 20 ml of 1N NaOH and 80 ml of methanol was added dropwise at -30°C over 30 minutes, and after the dropwise addition, stirring was continued at -30°C for 30 minutes. This reaction solution was quickly put into a dialysis membrane (Cellotube [F], molecular weight fractionation aooo, manufactured by Union Carbide), and immersed in a water-methanol mixed solvent (1:l) cooled to 0°C.
When dialysis treatment was performed for several days, a yellow precipitate was formed within the dialysis membrane. This precipitate was separated, dissolved in dimethylacetamide, cast, and dried under a nitrogen stream to obtain a precursor film.

The infrared absorption spectrum of this film is 1100ell.
Since absorption of ether bonds was observed in ', it was confirmed that the precursor polymer had a methoxy group in the side chain. Elemental analysis also confirmed that the thiophene ring contained a methoxy group.

In this way, a poly(3-methoxy-2,5-chenylenevinylene) precursor represented by the formula: (where n is approximately 1200) was obtained.

The temperature of the glass substrate and the ambient temperature were set to about 60°C, and poly(3-methoxy-2°5-chenylenevinylene)
A dimethylformamide (DMF) solution of about 2% by weight of the precursor was applied onto a glass substrate by a spin cord method and dried to form a precursor film.

At this time, the rotation speed of the spinner was 2000 revolutions per minute. The thickness of the obtained precursor film was approximately 800 mm.

Next, the glass substrate coated with the poly(3-methoxy-2,5-chenylenevinylene) precursor film was heated in an infrared image oven at 270° C. under a nitrogen stream for about 2 hours. As a result, the color of the precursor film changed from pale yellow to brown. By the above heat treatment, poly(
The 3-methoxy-2,5-chenylene vinylene) precursor film changes to a poly(3-methoxy-2,5-chenylene vinylene) film, and along with this, in the infrared absorption spectrum, C-C at 1590 cm-1 Absorption based on

Table 1 shows the nonlinear optical constants of the obtained PTV film.

Comparative Example 1 Table 1 shows the nonlinear optical constants of the precursor film obtained in the same manner as in Example 1.

Table 1 From the results shown in Table 1, it can be seen that the PTV film of Example 1 has a very large nonlinear optical constant. On the other hand, as the heat treatment temperature becomes lower in Examples 2 and 3, the nonlinear optical constant becomes smaller, and the nonlinear optical constant of the PTV precursor film of Comparative Example 1 is very small.
It can be seen that the TV precursor was converted into a π-conjugated polymer by heat treatment and exhibited a large nonlinear optical constant. It can also be seen that the nonlinear optical constant of the PTV film of Example 4 having a methoxy group on the thiophene ring is also very large.

[Effects of the Invention] As described above, the nonlinear optical material of the present invention is a π-conjugated material having a large nonlinear optical constant that can be obtained by forming a film by a simple method using a solvent-soluble precursor and then heat-treating the material. It is a polymer film and is a high-performance SHG active nonlinear optical material.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a manufacturer's fringe measurement system for determining nonlinear optical constants, and FIG. 2 is a graph showing manufacturer's fringe characteristics of the PTV film obtained in Example 1. (Drawing code) (1): YAG laser (21, polarizer (3): lens (4): rotation stage (5): thin film sample (6): filter (7): polarizer (8): photoelectric intensifier Multiplier (9): Boxcar integrator (10): Controller representative Yu Iwamasu, Jinto University

Claims (1)

[Claims] (1) General formula (I) obtained from solvent-soluble precursors
:▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) (In the formula, R^1 and R^2 are respectively -H, an alkyl group or an alkoxy group, and n is an integer.) A second-order organic nonlinear optical material composed of molecular compounds.