JPH0627507A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To provide an org. wavelength varying material having no significant absorption up to 400nm wavelength to be varied and excellent in thermal stability. CONSTITUTION:This org. nonlinear optical material is made of 4-methoxy-4'- chloro-alpha-cyanostilbene represented by the structural formula and having 340nm max. absorption wavelength lambdamax in 1,4-dioxane. This material has no significant absorption in the wavelength region of blue light, the m.p. is 126 deg.C and the SHG intensity measured by a powder method is twice that of urea.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to organic nonlinear optical materials. More specifically, it relates to a non-linear optical material used as an optical control element or the like in a wide field such as an optical computer and optical communication.

[0002]

2. Description of the Related Art Non-linear optical materials are optical frequency conversion elements,
It has been practically used as an optical shutter, an EO converter, and the like. Currently, KH ₂ PO is used as a nonlinear optical material.
₄ (KDP), LiNbO ₃ (LN), KTiOPO
Inorganic nonlinear materials such as ₄ (KTP), NH ₄ H ₂ PO ₄ (ADP), etc. (supervised by Kato and Nakanishi: Organic nonlinear optical material, published by CMC) are used. However, recently, attention has been paid to the magnitude of nonlinear optical constants of organic crystals, the speed of nonlinear optical response, and the like, and vigorous development is being carried out focusing on second-order nonlinear optical materials.

As organic nonlinear optical materials for secondary effects, 2-methyl-4-nitroaniline (MNA), 3-methyl-4-nitropyridine-oxide (POM), etc. have been developed, and secondary materials of MNA have been developed. The nonlinear constant is 50 of KDP
It doubles.

It is widely known that organic compounds exhibiting such a strong nonlinear effect generally have an electron-withdrawing group and an electron-donating group with a π-electron conjugated chain sandwiched therebetween. It is also known that the second-order nonlinear optical material must form a crystal without an inversion symmetry center.

[0005]

Since the inorganic nonlinear optical material has good crystallinity, a large crystal can be obtained, and the wavelength transmission region is wide. However, single crystals with high optical purity are very expensive, some have deliquescent properties, are inconvenient to handle, have poor optical damage strength, and have a small nonlinear optical effect. was there.

On the other hand, organic nonlinear optical materials typified by MNA have a large nonlinear optical effect, but have excellent weather resistance, and no crystal having good wavelength transparency has been found.

In addition, since one molecule of the organic nonlinear optical material is responsible for the origin of optical nonlinearity, the molecule having an asymmetric center has the second harmonic generation (SHG) activity in principle, but
When the SHG active molecule is crystallized and used as an optical element, it is often encountered that the SHG activity as a whole is lost. Therefore, it is necessary to actually synthesize the molecular material, crystallize it, and evaluate the optical nonlinearity to determine whether the organic material can be used as the nonlinear optical element.

In order to enhance the optical non-linearity of a single molecule, an electron donating and accepting substituent may be introduced into a long conjugated system. Furthermore, the optical non-linearity (supramolecular polarizability) of the organic compound at the molecular level can be estimated from the molecular orbital calculation. Stilbene-based molecules, which have a large supramolecular polarizability at the molecular level, are one of the typical organic nonlinear optical materials. For example, 4-methoxy-4'-nitro-α-cyanostilbenzene (HS Blair, NL Boyd; J. Soc. Dyers Colou
r, 92 , p14 (1976)), 4-methoxy-4'-bromo-stillylbenzene (GDDiana, PMCarabrese; Chem.Phys.Le.
tters, 144 , p79 (1988)), 4-methoxy-4'-nitro-stillylbenzene (H. Gusten, M. Salzwedel; Tetrahedr
on, 23 , p17 (1967)), 4-methoxy-4'-nitro-
α-Methylstilbenzene (Y.Wang, W.Tam, SHStevens
on, RAClement, J.Calabrese; Chem.Phys.Letters, 148 ,
pp2-3 (1988)) and 4-methoxy-4'-nitro-α.
-Bromostylbenzene (A. Yamaguchi, M. Okazaki; Journal of the Chemical Society of Japan, 91 , p2103 (1972)) has been reported. However, this type of material often has a center of symmetry in the crystalline state and becomes SHG-inactive as a crystal in many cases.

Considering the use as a wavelength conversion element, translucency in a molecular state or a crystalline state is an important factor.
For example, stilbene-based materials often exhibit a peak of light absorption spectrum in the visible light region. Since the stilbenzene skeleton has a long conjugated system, it has a strong electron-accepting substituent (nitro group, etc.)
It is predicted that when an electron-donating substituent (dimethylamino group, amino group, etc.) is introduced at the end of the conjugated molecule, it exhibits light absorption in the visible light region. Therefore, it is a problem to weaken the strength of the electron-accepting or donating substituent, to select the introduction position of the substituent in the stilbenzene skeleton, and to find a molecular material having no central symmetry as a crystal.

Considering the same use as in the conventional inorganic nonlinear optical element, it is desirable that the molecular material has a high melting point.
However, the melting point of the organic material is generally about 100 ° C., and the temperature coefficient of the refractive index that determines the phase matching condition is large.
The temperature tolerance of the wavelength conversion element tends to be low.

[0011]

Thus, according to the present invention, there is provided an organic non-linear optical material comprising 4-methoxy-4'-chloro-α-cyanostilbenzene.

Stillebenzene compounds are characterized by a pi-electron conjugated system which is longer than benzene and styrene-based non-linear optical materials. Therefore, in consideration of the well-known trade-off relationship between the non-linear constant and translucency, a very large electron accepting (nitro group, etc.) and electron donating (dimethylamino group, amino group, etc.) substituent is used as a conjugated system. It is important to avoid introducing them at the same time. The optical non-linearity and the maximum absorption wavelength of a single molecule were estimated by molecular orbital calculation (PPP method) for a molecular species in which a cyano group was introduced near the center of a stilbenzene conjugated system as an electron-accepting substituent.
Examples of the electron-donating substituent include a methoxy group and a chloro group,
A cyano group was selected as the electron-accepting substituent, and the position of the substituent to be introduced was examined. The size of the substituent,
Considering the rotational degree of freedom and rigidity, the reason for selection was that the substituent itself does not have a center of symmetry. This led to the discovery of a material that exhibits optical nonlinearity in the crystalline state.

[0013]

EXAMPLES The synthesis of 4-methoxy-4'-chloro-α-cyanostilbenzene will be described.

P-anisaldehyde 1.79 g (0.0
(13 mol) in 150 ml of ethanol,
2 g (0.013 mol) of chlorobenzyl cyanide was added. 10 ml of an ethanol solution in which 0.7 g of sodium ethylate was dissolved was added dropwise thereto. After stirring this solution at room temperature for 6 hours, the formed precipitate was filtered,
After washing with methanol, a compound of the following structural formula 4-
1.79 g of methoxy-4'-chloro-α-cyanostilbenzene was obtained. The yield was 51%.

[0015]

[Chemical 1]

The absorption spectrum of this compound is shown in FIG. When the maximum absorption wavelength is measured from Fig. 1, it is 340 nm.
(In 1,4-dioxane). The melting point was 126 ° C. as measured by DSC. This is methyl-
(2,4-Dinitrophenyl) -aminopropanoate (MAP; JLOudar and R. Hierle, J. Appl. Phys., 48 (1
977) 2699) melting point much higher than 69 ° C.

Next, evaluation of the second harmonic generation (SHG) of the obtained fine powder crystal was carried out by the powder method (SK Kurtz, TTPerry: J.
Appl. Phys (39) 3788 (1968)). When a fine powder crystal is irradiated with an Nd-YAG laser (wavelength = 1.064 µm), a second harmonic wave is generated (SHG), which is 1/2 of the incident light.
The green light of the wavelength (532 nm) was observed. This SH
It was confirmed that the G intensity was twice as high as the urea ratio, and the SHG efficiency was stronger than that of urea.

Further, a crystal on the plate was easily obtained by the recrystallization operation from ethanol, and a single crystal could be produced by using this as a seed crystal.

Comparative Example The present inventors have introduced a methoxy group at the 2-position of the phenyl group (β-position) of 4′-chloro-α-cyanostilbenzene (a) and methoxy at the 3-position as follows. A group (b) having a group introduced and a group (c) having a cyano group introduced at the 3-position were synthesized in the same manner as in the above Examples to obtain crystals. However, as a result of evaluating this compound by the powder method,
The SHG was inactive.

[0020]

[Chemical 2]

[0021]

EFFECT OF THE INVENTION 4-Methoxy-4'-chloro-of the present invention
The organic nonlinear optical material made of α-cyanostilbenzene has a high melting point of 126 ° C. and is very stable thermally. Furthermore, since the absorption edge is on the short wavelength side and exhibits high SHG activity, it can be used in a wide range of fields as a nonlinear optical element. Further, by using such an organic material excellent in optical nonlinearity, translucency, and temperature tolerance of the phase matching condition, the characteristics of an expensive inorganic nonlinear optical material can be provided at a low price by the organic material.

[Brief description of drawings]

FIG. 1 shows the relationship between wavelength and absorbance in 1,4-dioxane of 4-methoxy-4′-chloro-α-cyanostilbenzene.

Claims (1)

[Claims] 1. An organic non-linear optical material comprising 4-methoxy-4′-chloro-α-cyanostilbenzene.