JPH05273614A - Nonlinear optical material - Google Patents

Abstract

PURPOSE:To enhance three-dimensional nonlinearity, to prevent occurrence of thermal and optical damage due to laser beams and to improve solubility in the material to be used by incorporating a specified compound prepared by conbining a pi electron-conjugated type dyestuff with helicene (Z) having a vinylene group in it. CONSTITUTION:This nonlinear optical material contains the compound prepared by combining the pi electron-conjugated type dye stuff with the helicene (Z) having the vinylene group in it represented by the formula Z-CH=CH-D. It is preferred that the helicene Z is optically active in order to apply various signal processing methods especially for reading out the change of the refractive index. The compound of this formula is enhanced in nonlinearity by nonloclized pielectrons enlarged by the vinylene group (-CH=CH-) and the pi electron- conjugated dye D. On the other hand, since the spiral electron system of the helicene combines with the straight chain pi electron system, intermolecular interaction does not become too great and its solubility in solvents is not lowered, and accordingly, its synthesis and manufacture of a device by using it is made easy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical material useful in the fields of optoelectronics, optical information processing, optical communication and the like.

[0002]

2. Description of the Related Art Nonlinear optical materials are materials that exhibit a second-order or higher nonlinear response under a strong electric field of laser light, and are important materials in optical signal processing such as frequency conversion, oscillation, and switching. is there. In particular, the third-order nonlinear optical material has been attracting attention as a basic material for next-generation optical communication and information processing, which fully exhibits the excellent characteristics of light such as high speed and parallelism.

Of these nonlinear optical materials, organic nonlinear optical materials are particularly important because there are materials that have faster response and larger nonlinear optical constants than conventional inorganic nonlinear optical materials. Although the mechanism of manifestation of the third-order nonlinear optical effect has not been clarified yet, it is known that, for example, one having a large delocalized π-electron system exhibits the third-order nonlinear characteristic.

Conjugated polymers such as polydiacetylene and conjugated dyes such as stilbenes and cyanines are known as those having a delocalized π-electron system. In addition, since helicenes having a helical structure in which five or more aromatic rings are connected have a large delocalized π-electron system, they have a large third-order nonlinearity and are free from thermal and optical damage, and third-order nonlinear optics. Excellent as a material.

However, helicenes, in which many aromatic rings are connected, are extremely inferior in solubility in a solvent due to intermolecular interaction of π electron system and highly symmetrical structure. Therefore, it is difficult to handle a high-concentration polymer dope, etc., which is necessary when using it as a device material for optical information processing, and the solubility of the synthetic intermediate is also reduced. However, there is a problem in that efficient synthesis is difficult.

On the other hand, the third-order nonlinear optical material attempts to utilize the fact that the refractive index changes with the irradiation of light. As a method of reading this change in refractive index, for example,
A method for amplifying a minute change in the refractive index using a Fabry-Perrot resonator has been proposed. However, in this method, the slight instability of the light source sensitively affects the resonance stability, so the entire system is extremely delicate. However, the high dimensional quality accuracy for stable operation of this is an obstacle in terms of cost and mass production. Further, in order to increase the refractive index change, extremely high energy has to be injected, and there are problems such as the heat resistance of the material, the thermal effect, and a technical barrier for putting information on the high injection energy.

As a method of improving this, there has been proposed a method of detecting with extremely high sensitivity by elliptical polarization measurement of weak probe light. In this method, strong excitation light induces optical anisotropy in a substance to generate a change in polarization of linearly polarized signal light. In this method, it is necessary to make the excitation light circularly polarized in order to utilize the optically induced optical anisotropy, or to incline the polarization direction of the excitation light from the polarization direction of the signal light. There was a limit to the method.

[0008]

The object of the present invention is to solve the above-mentioned problems, to exhibit a large third-order nonlinearity, to be free from thermal and optical damage by a laser, and to have good solubility in a solvent. Thus, it is an object of the present invention to provide a non-linear optical material which can be easily synthesized and made into a device and to which various signal processing methods can be applied to read a change in refractive index.

In the present invention, the helicene Z has a vinylene group (-
CH = CH-), and a non-linear optical material containing a compound represented by the general formula; Z-CH = CH-D, in which the π-electron conjugated dye D is bonded. In particular, in order to apply various signal processing methods for reading changes in the refractive index, it is desirable that the helicene Z is an optically active substance.

Examples of helicenes Z include carbohelicene and heterohelicene. Carbohelicene is a compound having a helical structure in which five or more aromatic rings, preferably 6 to 20, are connected. Heterohelicene is a compound composed of a co-condensed ring of benzene and a heterocycle such as thiophene, furan, pyridine and pyrrole.

Such carbohelicene and heterohelicene are described, for example, in Top.Curr.Chem.125 (Stereochemistr
y), 63-130 (1984). The method for synthesizing carbohelicene and heterohelicene is not particularly limited, but for example, it was synthesized by Wittig reaction or Siegrist reaction.
It can be obtained by photocyclization of 1,2-diarylethylenes, bis (arylvinyl) arenes and the like.

As the π-electron conjugated dye D, p-nitrostilbene, DANS (4-N, N-dimethylamino-
4'-nitrostilbene), DEANS (4-N, N-
Examples thereof include stilbenes such as diethylamino-4′-nitrostilbene) and cyanines such as DOCI (3,3′-diethyloxacarbocyanine) and DODCI (3,3′-diethyloxadicarbocyanine).

Particularly, one having an electron-withdrawing group on one side is preferable. This is because the electron-donating helicenes and the electron-withdrawing group are bonded to the linear π-electron conjugated system to realize a structure that further enhances the nonlinear effect.

In the compound represented by the general formula of the present invention; Z-CH = CH-D, the delocalized π-electron system is expanded by the vinylene group (-CH = CH-) and the π-electron conjugated dye D, and the nonlinear The property is improved. On the other hand, since a linear π-electron system -CH = CH-D, which is different from the helical electron system of helicenes, is connected, the interaction between molecules does not unnecessarily increase, and therefore the solubility in a solvent is high. Does not fall. Therefore, synthesis and deviceization are easy.

The non-linear optical material of the present invention is a helicene Z
It is synthesized by introducing a formyl group into and then reacting with Wittig reagent. There are many methods for introducing a formyl group into helicenes, but the most effective and versatile method is the electrophilic substitution reaction, which is generally known as a Friedel-Crafts type reaction. There is a method of formylating the electron donative substitution position to
Many kinds of formylation reaction reagents are known, and one suitable for the reactivity of helicene is used. This substitution position and reactivity are predicted with high accuracy for ordinary planar type aromatic compounds, but sufficient studies have not yet been made in the case of helicenes having a distorted planar structure. Then, as a result of a detailed study by the present inventors, it was found that a formyl group can be introduced with extremely high efficiency.

For example, in the case of hexahelicene, which is a 6-membered helicene, the 5-position and 8-position shown in FIG. 1 are substitution positions that are susceptible to formylation. A suitable reaction reagent is, for example, dichloromethyl alkyl ether, which can introduce a formyl group at the 5-position and the 8-position in high yield.

The synthesis of Wittig reagents is a well-established method with many examples known. Synthesis of helicene derivative by Wittig reaction is carried out according to a conventional method by using formylhelicene and Wi
The ttig reagent can be easily performed in good yield.

As described above, by introducing a formyl group into helicenes and further conducting the Wittig reaction, the general formula; Z-CH =
Obtaining the compound represented by CH-D is a very versatile and efficient method. Moreover, such a compound is an effective material that has both a large π-electron conjugated system and easy handling, and is extremely useful.

In the present invention, even if an optically active substance is used as the helicene, the same synthesis can be performed. Further, a compound represented by the general formula; Z-CH = CH-D can be optically resolved to obtain an optically active substance.

Of the compounds represented by the general formula of the present invention; Z-CH = CH-D, the compounds in which the helicene Z is an optically active substance have chiral properties and therefore depend on the intensity of light for linearly polarized light. And has the property of rotating the plane of polarization.

In this case, the absorption spectrum and the refractive index dispersion cause a frequency shift between the L polarized light and the R polarized light. The refractive index for L polarized light is n _L , and the refractive index for R polarized light is n _R
Then, the optical rotatory power is caused by (n _L −n _R ), and the polarization rotation angle is πl / λ (n _L −n _R ) where l is the sample length and λ is the wavelength.

Next, when the nonlinear refractive index change is caused by the strong linearly polarized light excitation, it is considered that the linearly polarized light is a combination of left and right circularly polarized light. Therefore, it acts on both n _L and n _R , and the refractive index is Change. This nonlinear refractive index change is expressed as Δn
_{If L} and Δn _R , the polarization rotation angle due to the nonlinear effect is πl / λ [(n _L −n _R ) − {(n _L + Δn _L ) − (n
_R + Δn _R )}] = πl / λ (Δn _L −Δn _R ). That is, it is considered that the polarization rotation occurs according to the difference in the nonlinear refractive index change between the L-polarized light and the R-polarized light. Further, this effect is expected to increase as the optical activity increases.

Therefore, the general formula of the present invention; Z-CH =
Among the compounds represented by CH-D, when helicenes Z irradiate a compound which is an optically active substance with linearly polarized light, by detecting the change in the rotation angle of the polarization plane by changing the intensity of light. You can By using this characteristic, the elliptic polarization analysis method described above can be used to perform similar measurements on linearly polarized light in the same direction as the signal, without elaborating on the polarization of the excitation light. Processing becomes possible.

Further, the excitation light and the signal light are made into one linearly polarized light, and the signal waveform can be controlled by self-rotation by the intensity of the light. Furthermore, by using a highly repetitive pulse light source, higher sensitivity and accuracy can be secured in combination with the high frequency polarization modulator. Therefore, it can be suitably used as a device material for optical communication, optical information processing and the like.

[0025]

EXAMPLES Examples will be shown below. Synthesis Example 1 (Synthesis of formylhexahelicene) 0.2 g of hexahelicene was dissolved in 20 ml of dichloromethane,
Under ice cooling, 0.159 g of tin tetrachloride and 0.084 g of dichloromethyl methyl ether were added, and the mixture was stirred for 30 minutes. Furthermore, diluted hydrochloric acid was added at room temperature for 1 hour, and the mixture was stirred for 30 minutes. The reaction was carried out under a nitrogen stream. After extraction with dichloromethane, evaporation of the solvent and purification by column chromatography, yellow powder of formylhexahelicene (2: 1 mixture of 5-substituted and 8-substituted) 0.16
got g. Pure sample of each isomer was recrystallized and HP
Obtained by LC.

Synthesis Example 2 (Synthesis of Wittig reagent) 3.40 g of p-nitrophenylacetic acid and 2.2 of p-tolualdehyde
6 g was stirred in 1.5 ml piperidine at 140 ° C. for 2.5 hours. After cooling, the filtered product was washed with methanol and recrystallized with ethanol to obtain 2.27 g of 4-nitro-4′-methylstilbene. Next, 2.0 g of this 4-nitro-4'-methylstilbene
And 1.49 g of N-bromosuccinimide (NBS) were refluxed in 8 ml of carbon tetrachloride for 7 hours. After adding 0.3 g of NBS and refluxing for 8 hours, the mixture was filtered while hot, the filtrate was washed with 0.1N sodium thiosulfate, dried over magnesium sulfate, and the solvent was distilled off to obtain 2.5 g of a yellow powder. This yellow powder
2.5 g of triphenylphosphine and 2.4 g of triphenylphosphine were refluxed in 40 ml of xylene for 1 hour, filtered while hot, washed with xylene and petroleum ether, and red-brown powder of p- (p-nitrostyryl) benzyltriphenylphosphonium bromide 3.4 g. Got

Synthesis Example 3 (Synthesis of helicene derivative by Wittig reaction) 37 mg of formylhexahelicene obtained in Synthesis Example 1 and 73 mg of p- (p-nitrostyryl) benzyltriphenylphosphonium bromide obtained in Synthesis Example 2 were mixed with benzene. The mixture was stirred in 1 ml at 70 ° C., and an equimolar amount of a solution of sodium ethoxide in benzene was added dropwise. After refluxing for 1 hour, the mixture was stirred at room temperature overnight. The reaction was carried out under a nitrogen stream. After the solvent was distilled off, it was purified by column chromatography to give 5- [p- (p-nitrostyryl) phenylenevinylene] hexahelicene and 8-
47 mg of a light-colored powder of [p- (p-nitrostyryl) phenylenevinylene] hexahelicene (2: 1 mixture of 5-isomer and 8-isomer) was obtained. Separation of isomers was performed by recrystallization or HPLC. The optical resolution is HPLC
Went by.

Both the 5-isomer and the 8-isomer showed strong absorption at about 410 nm due to the introduced dye. FIG. 2 shows a UV and CD spectrum chart measured with a chloroform solution.

Example 1 5- [p- (p-nitrostyryl) obtained in Synthesis Example 3
Third-order nonlinear optical characteristics were measured using a polarization / nonlinear constant measuring device shown in FIG. 3 using a THF solution of phenylenevinylene] hexahelicene. The light source is the third harmonic (355 nm) of the Q-switched Nd: YAG laser 1.
This output light is split into a pump light 11 and a probe light 21 using a dye laser 2 by excitation, and is linearly polarized by a polarizer P1 and a polarizer P2, respectively. After passing through the sample 3, the probe light 21 is quenched by the analyzer P3. Here, the polarization planes of the pump light 11 and the probe light 21 are 45 °.
The sample 3 was irradiated at an angle of. Analyzer P3
The light that passed through was detected by the photomultiplier tube 5 through the spectroscope 4. As a result, the third-order nonlinear susceptibility measured at the absorption edge wavelength (540 nm) was about 5 times larger than that of hexahelicene and 5-nitrohexahelicene in 100% conversion.

The solubility in THF was 2% or more, which was equivalent to that of 5-nitrohexahelicene. On the other hand, as compared with the 13-membered ring tridecahelicene, the third-order nonlinear susceptibility was almost the same, and the solubility in THF was 20 times or more.

Example 2 THF of (+)-5- [p- (p-nitrostyryl) phenylenevinylene] hexahelicene obtained in Synthesis Example 3
The solution was used to measure the chiral nonlinear effect by the polarization / nonlinear constant measuring device shown in FIG. Probe light 2
1 is linearly polarized by the polarizer P2, passes through the sample 3, and is then extinguished by the analyzer P3. Here, when the sample 3 was irradiated with the linearly polarized pump light 11 having the same polarization direction as the probe light 21 by the polarizer P1, bleeding light due to the chiral nonlinear effect was detected.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a method for synthesizing [p- (p-nitrostyryl) phenylenevinylene] hexahelicene.

FIG. 2 shows UV and CD spectra of (+)-5-isomer and (+)-8-isomer of [p- (p-nitrostyryl) phenylenevinylene] hexahelicene. ..

FIG. 3 is a schematic diagram of a polarization / nonlinear constant measuring device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Morita 8-1 Goi Minamikaigan, Ichihara City, Chiba Ube Industries Ltd. Chiba Research Institute

Claims (2)

[Claims] 1. The helicene Z has a vinylene group (—CH═C).
A non-linear optical material containing a compound represented by the general formula; Z-CH = CH-D, which is sandwiched between H-) and a π-electron conjugated dye D. 2. The non-linear optical material according to claim 1, wherein the helicene Z is an optically active substance.