JPH03230127A - Aromatic nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain an optical material having high secondary nonlinear optical characteristics by using a crystalline compd. made of a solid soln. of p- nitroaniline in carboxylic acid. CONSTITUTION:A nonlinear optical material is formed with a compd. made of a solid soln. of p-nitroaniline in carboxylic acid represented by formula I, wherein n is 0, 1 or 2, Ar is 5-14C arom. group, each of X and Y is functional group selected among ether represented by R1-O, amino represented by -N(R2)R3, thio-ether represented by -SR4, cyano, nitro, ester represented by -COOR5 or -COCR6, amido represented by -CON(R7)R8 or -N(R9)COR10 and hydrocarbon represented by R11 and each of R1-R11 is H or 1-8C hydrocarbon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to nonlinear optical materials, and more particularly to organic aromatic materials having large second-order nonlinear optical properties.

[Conventional technology]

A nonlinear optical effect is a nonlinear optical effect that, when a strong optical electric field such as that of a laser beam is applied to a material, the electric polarization response of the material is linearly proportional to the magnitude of the applied electric field. This refers to the appearance of higher-order effects than the following.

Second-order nonlinear optical effects include second harmonic generation, which converts the wavelength of incident light by 1/2, parametric oscillation, which converts light of one type of wavelength into two types of light, and conversely, two types of wavelength conversion. There is secondary light mixing, which produces light of one type of wavelength from the light of . Due to these characteristics, materials with nonlinear optical effects will be used in the future as optical switches and optical memories used in optical data processing, information processing, or optical communication systems, or optical bistable devices used in optical signal processing. It may be used as an element such as an optical switch. Generally, in this field, inorganic materials are being researched and considered, mainly LiNbO3, but inorganic materials do not have a very large figure of merit and have a low response speed.
It has drawbacks such as poor formability, high hygroscopicity, and low stability, making it difficult to form a desired optical element.

In recent years, many attempts have been made to investigate organic materials in place of these inorganic materials.

It has been confirmed and reported that the response of the organic substance is mainly based on the polarization of the π-electron system, so the nonlinear optical effect is large and the response speed is also large. For example, Acinis Symposium Series, Volume 233 (AC3
Symposium Series Volume 233, 19
Many examples have been reported in 83). In the present invention, since the second-order nonlinear optical property in question is a third-order tensor, it will not become apparent if a center of interest exists in a molecule or crystal. For this reason, even though organic substances have a large molecular nonlinear susceptibility at the molecular level, at the solidification and crystallization stages, due to the polarization effect that is the background that causes the large nonlinear susceptibility to appear. Therefore, a stable centrally symmetrical structure is preferentially formed, which causes the problem that no second-order nonlinear optical effect is exhibited as an optical element. In general, the second harmonic generation ability increases in long conjugated systems where the polarization within the molecule is large and the contribution of that polarization is large, but conversely, when the conjugation length becomes long, the absorption wavelength shifts to the longer wavelength side. , which corresponds to 1/2 wavelength of the incident light. At that time, the second harmonics generated may be absorbed, resulting in optical damage that changes the refractive index, chemical denaturation, or combustion due to absorption of thermal energy. Therefore, simply increasing the conjugate length is often not advantageous.

For example, compounds with increased molecular polarization by introducing groups with large electron-withdrawing properties such as carboxyl groups and cyano groups as shown in formula (1) below, and various substituents on the benzene ring, As a result of the transfer effect of the electron configuration within the ring,
Large nonlinearity is expected, but in reality, due to the magnitude of the molecular polarization, the structure has a center of inversion symmetry,
Generation of the second harmonic is often not observed. in general,
Controlling crystal structure is a difficult technique, and it is especially difficult to create a crystal system that breaks the center of symmetry.

In order to overcome this difficulty, the present inventor first applied for an invention utilizing an optically active chiral structure and filed a patent application on Patent Application No. 63-7.
No. 2080, Japanese Patent Application No. 63-720821), they succeeded in directly expressing the nonlinear susceptibility at the molecular level in the crystal structure.

On the other hand, 2-methyl-4-nitroaniline (MNA) is a typical material having high second-order nonlinear optical properties. This compound is designed to prevent p-nitroaniline, which inherently has high single-molecule nonlinear susceptibility, from forming a center of inversion symmetry during crystallization due to the polarization effect by introducing a methyl group. This is a developed material. If p-nitroaniline itself could have a structure without a center of inversion symmetry, not only would there be no need to newly synthesize it, but the effect of a simple structure with high polarization efficiency could be fully expressed, and the industrial significance would be It is considered to be large.

(Problems to be Solved by the Invention) The present invention aims to provide a crystalline compound of p-nitroaniline without inversion symmetry, which has increased ability to generate second-order nonlinearity for various nonlinear optical elements. purpose.

[Means for Solving the Problems] The present invention has the following general formula (1) % formula % (1) [where n is 0.1 or 2 and Ar is a carbon number of 5 to 14]
aromatic group, X, Y are the same or different, R, -0-
Ether group represented by N (R2)R, amino group represented by S Ra, cyano group, nitro group, -COO
R2, an ester group represented by -0COR, -CON
(R7)Ra, -N (R1)COR,.

represents a functional group selected from the group consisting of an amide group represented by -R, and a hydrocarbon group represented by -R, where R0 to R8
is the same or different and represents a hydrocarbon group having 1 to 8 carbon atoms or a hydrogen atom) This is a nonlinear optical material characterized by being composed of a solid solution of a carboxylic acid represented by the following and p-nitroaniline.

In general formula (1), Ar represents an aromatic group having 5 to 14 carbon atoms. Examples of this Ar include groups derived from pyridine, benzene, biphenyl, indene, naphthalene, biphenylene, acenaphthylene, fluorene, phenanthrene, anthracene, benzofuran, hendithiophene, indole, quinoline, isoquinoline, carbazole, and xanthine. . Among these, groups derived from benzene or naphthalene are preferred.

In addition, in general formula (1), when either X or Y is a hydrogen atom, the substituent other than the hydrogen atom is preferably located at the p-position or 〇-position with respect to the -CH=CH- group, and both are hydrogen atoms. In the case of atoms other than atoms, it is preferable that they are in the p-position and the ○-position.

In order to enhance the nonlinear optical effect, it is necessary to have a large dipole in the molecular structure, and for this purpose, general formula (I) has a cyano group and a carboxyl group present on the same carbon atom. let

In addition, it is desirable to have a conjugated system in order for the molecular polarizations to interfere with each other, but as the conjugation length increases, the absorption maximum extends toward longer wavelengths, causing damage due to the incident light wavelength or second harmonic. There is a possibility that this may occur. For this purpose, p-nitroaniline, whose conjugation length must not be too long, can be used as a commercially available product as it is or after recrystallization and purification from an appropriate solvent.

The solid solution of the present invention is preferably formed of the carboxylic acid of general formula (1) and p-nitroaniline in a molar ratio of 1:5 to 5:1.

Formation of the solid solution can be carried out by mixing in the melt, solid phase or in a suitable solvent. Preferred examples of such solvents include alcohols such as ethanol and methanol, and cyclic ethers such as dioxane and tetrahydrofuran.

In addition, the method of forming a solid solution from the melt is more preferable from the viewpoint of operability, but from the viewpoint of stability of the compound, it is not preferable to perform it at too high a temperature, and it is preferable to set the temperature near the melting point of P-nitroaniline. Desirable from both operability and stability.

The thus obtained solid solution of carboxylic acid and p-nitroaniline takes the form of a crystal, has excellent moldability, can be shaped into various devices, and can be applied to nonlinear optics applications.

〔Example〕

The present invention will be explained in more detail below using Examples.

In addition, in the examples, unless otherwise specified, % is based on weight.

Furthermore, in the examples, the second harmonic generation was measured as follows.

That is, Nis, K. Kurz (S, KKur
Journal of Applied Physics (J, Appl.

This was carried out on the powder of the present invention according to the method described in Ph)'S, Volume 39, Page 3798 (1968). Nd:YAG laser (2KW/
2Hz pulse) 1. This was done by irradiating a powder sample filled in a glass cell with a light beam of 0.6 μm and detecting the green light generated.

Add 2.51 g of methyl cyanoacetate to 40 m2 aqueous solution containing 1.72 g of sodium hydroxide, and add p
-Add 2.76g of methoxycinnamaldehyde,
Heat to 5°C and continue stirring for 40 hours. After the reaction was completed, the solid was collected in addition to 12N hydrochloric acid.

This solid was recrystallized from a methanol/water mixed solvent to obtain the desired product 2.
．． 7g was obtained. The melting point of this product is 230°C. Elemental analysis values are: C: 6B, oo%, H: 4.90%, N: 5.
99%, calculated value c: 68.10%, H: 4.8
5%, N: 6.11%, showing good agreement.

The absorption maximum wavelength in the ultraviolet-visible spectrum was 375 nm (in methanol solvent).

After dissolving 30.39 g of methyl cyanoacetate in a 400d aqueous solution containing 12.77 g of sodium hydroxide, 29.76 g of p-nitrobenzaldehyde was dissolved in a nitrogen atmosphere.
g was added thereto, and stirring and heating under reflux were continued for 51 hours. After the reaction,
It was added to 12N hydrochloric acid and the precipitate was collected. This solid was repeatedly recrystallized from methanol to obtain crystals in a yield of 51%.

Melting point: 207°C1 Elemental analysis values: C: 55.91%, H
: 2.93%, N: 12.80%, and the calculated value of C:
55.02%, H: 2.15%, N: 12.84%, showing good agreement.

λ□ was 302 nm.

Precept 1 - Instead of 29.76g of p-nitrobenzaldehyde, 3
The reaction with methyl cyanoacetate was carried out in an aqueous sodium hydroxide solution in the same manner as in Reference Example 2, except that 25.38 g of ,4-dimethoxybenzaldehyde was used, and the obtained solid was recrystallized twice from ethanol to obtain the desired product. 19.84
I got g.

Melting point is 206.1°C1 Elemental analysis value is C: 61.94%
, Hl, 78%, N: 6.04%, and the calculated value of C:
61.79%, H: 4.76%, N: 6.01%, showing good agreement.

λsaX was 353 nm.

The infrared absorption spectrum contains C at a wave number of 2,221 cm-'.
N group, 1,956 cm-' 1 573 cl'1,
The presence of a benzene ring and a conjugated double bond was observed at 512 cm-'.

4-9 Carbom 4- Various carboxylic acids shown in Table 1 in the same manner as in Reference Example 3 [
Compounds (4 to 9)] (corresponding to Reference Examples 4 to 9, respectively) were synthesized.

1 A
] 2.09 g of compound (1) obtained in Reference Example 1 and 2.6 g of p-nitroaniline were mixed well in powder form, dissolved in 60 all of ethanol with oil at 70°C, and the homogeneous solution was cooled to room temperature. 4.0 g of yellow crystals were obtained.

When this solid was pulverized and its ability to generate second harmonics was examined, it was found to have an intensity approximately 10 times that of urea.

2 B reference example 1
Compound (1) obtained in 2. (Mix jg and 2.5 g of P-nitroaniline in powder form and heat at 160°C.
It was left standing for 20 minutes.

The mixed system became a homogeneous liquid, and when cooled to room temperature, a crystalline solid precipitated.

When this crystal was thoroughly crushed and its ability to generate second harmonics was examined, it showed an intensity approximately 16 times that of urea.

3 to I4, the formation method (A) of Example 1 or the formation method of Example 2 (
In B), a solid solution of the compound shown in Table 2 with p-nitroaniline was prepared, and its second harmonic (SHG) generation ability (relative to urea) was investigated.

The results are shown in Table 2.

Table 2 [Effects of the Invention] The crystalline compound of p-nitroaniline without inversion symmetry of the present invention has a large nonlinear optical effect, so it is suitable for optical data processing.
It can be used as an element such as an optical switch, an optical memory used in information processing or an optical communication system, or an optical bistable element or an optical switch used in optical signal processing.

Claims (1)

[Claims] (1) The following general formula (I) ▲ Numerical formulas, chemical formulas, tables, etc. are available▼ ... (I) [In the formula, n is 0, 1 or 2, and Ar has 5 to 14 carbon atoms.
aromatic group, X and Y are the same or different, R, -O-
Ether group represented by -N(R_2)R_3, amino group -SR_4
thioether group, cyano group, nitro group, -C
Ester group represented by OOR_5, -OCOR_6, -
CON(R_7)R_8, -N(R_9)COR_1_
Indicates a functional group selected from the group consisting of an amide group represented by 0 and a hydrocarbon group represented by -R_1_1, where R_
1 to R_1_1 are the same or different and represent a hydrocarbon group having 1 to 8 carbon atoms or a hydrogen atom] A nonlinear optical material comprising a solid solution of a carboxylic acid represented by the following and p-nitroaniline.