JPH07111529B2 - Organic nonlinear optical material - Google Patents

Description

TECHNICAL FIELD The present invention relates to an organic nonlinear optical material, and more specifically, it can be used as a light control element in a wide range of fields such as optical computers and optical communications 4- [2] It relates to an organic nonlinear optical material composed of-(4-nitrophenyl) ethenyl] benzaldehyde.

<Prior Art> Non-linear optical materials cause phenomena such as frequency conversion, amplification, oscillation, and switching of laser light, and generate second harmonic (SHG), third harmonic (THG), high-speed shutter,
It can be applied to optical memories and optical arithmetic elements.

In this way, nonlinear optical materials have the function of converting the optical frequency, and because they can be applied to optical switches that take advantage of the property that the refractive index changes with an electric field, active research is underway. Has been.

Conventionally, water-soluble KH ₂ P has been mainly used as a nonlinear optical material.
O ₄ (KDP), NH ₄ H ₂ PO ₄ or water-insoluble LiNbO ₃ , KNbO ₃
Inorganic single crystal materials (dielectric crystals) have been used, but recently urea, p-nitroaniline, 2-methyl-4-nitroaniline (MNA), 4 '-(N, N'- Organic nonlinear optical materials such as dimethylamino) -4-nitrostilbene (DANS) are being developed. Polymer organic materials such as polydiacetylene and polyvinylidene fluoride are also being investigated for application to waveguides having control functions, optical ICs, etc. by utilizing their nonlinear optical effects.

Organic nonlinear optical materials do not have lattice vibrations with respect to optical response because the origin of nonlinearity is intramolecular π electrons, and therefore have a faster response than inorganic materials, and have a large nonlinear optical constant or absorption region. It is possible to compose things that can change. Moreover, the method for forming the material element is not limited to single crystallization, and various methods such as LB film, vapor deposition method, liquid crystal, and polymerization can be considered.

Regarding the research on these nonlinear optical materials, for example, "Organic Nonlinear Optical Materials" edited by Masao Kato, Hachiro Nakanishi (CMC, published in 1985), "Nonlinear Optical Proper"
ties of Organic Molecules and Crystals Vol.I and Vo
Recent research status is summarized in the literature such as l.II DSCHEMLA, J.ZYSS edition (ACADEMIC PRESS, published in 1987).

By the way, among the nonlinear optical effects required as a nonlinear optical material, the second harmonic generation (SHG) is positioned as a basic technique of wavelength conversion because of its high conversion efficiency. In addition, a material with a large effective nonlinear optical constant is required for efficient SHG. And, as described in detail in the above literature, it is necessary that the crystal does not have a center of symmetry in order to exhibit SHG activity.

Nonlinear optical inorganic materials generally have good crystallinity and can easily obtain large crystals, but they have the drawback of having a small nonlinear optical constant as compared with organic materials. On the other hand, it is known that some nonlinear optical organic materials generally have large nonlinear optical constants, but it is difficult to prepare stable and large organic crystals at room temperature.

For example, among the conventionally known organic crystals, MNA has a SHG activity because it has no symmetry center, and it is reported that the second harmonic generation efficiency is about 2000 times that of LiNbO ₃ . . However, MNA has a drawback that it is not practical because it is difficult to obtain a large single crystal. Further, although urea can easily obtain a large single crystal, it has the drawbacks of low SHG activity and poor moisture resistance. The molecular polarizability β of DANS shows a very large value at the molecular level, but the organic crystal DANS does not show SHG activity because it has a symmetry center when it becomes a crystal.

Therefore, the development of an organic nonlinear optical material that forms a single crystal having no center of symmetry, has a large effective nonlinear optical constant, and thus has a large SHG activity, is currently most demanded. Further, in practical use as a non-linear optical material, it is desired to form a single crystal which is stable at room temperature and is as large as possible. However, SH
Organic nonlinear optical materials with high G activity, stable, and easy to grow into large single crystals have not yet been provided.

<Problems to be Solved by the Invention> An object of the present invention is to overcome the problems of the above-mentioned prior art, form a single crystal that is stable at room temperature, and that has no center of symmetry. It is to provide an organic nonlinear optical material having a large SHG activity that can be grown to a high temperature.

As a result of intensive studies, the present inventors have found that a specific stilbene derivative forms an organic crystal having a large SHG activity, and have completed the present invention based on the findings.

<Means for Solving the Problems> That is, according to the present invention, the following general formula An organic non-linear optical material characterized by comprising 4- [2- (4-nitrophenyl) ethenyl] benzaldehyde represented by

Hereinafter, the components of the present invention will be described in detail.

The stilbene derivative in the present invention has a structure having a formyl group and a nitro group in each phenyl group of stilbene (trans isomer of diphenylethylene).

The stilbene derivative of the present invention has good crystallinity, and a single crystal can be easily obtained from an organic solvent by a slow evaporation method or the like, and the single crystal is stable at room temperature.

Further, the single crystal of the stilbene derivative of the present invention is about the same as urea.
As is clear from the fact that it shows 2.5 times the SHG efficiency, it is a single crystal with no center of interest.

DA, which is the same stilbene derivative and has the following structural formula
NS has a large molecular polarizability, but its organic crystal has an effective nonlinear optical constant of 0.0 due to the symmetry of the crystal.
In view of its lack of HG activity, it is unexpected that the stilbene derivative of the present invention having a formyl group forms an organic crystal exhibiting excellent SHG activity.

The stilbene derivative of the present invention makes it possible to break the crystal symmetry by introducing a formyl group as a nuclear substituent at the 4-position (rose position) of one phenyl group.
It can be inferred that the activity could be expressed.

<Examples> Hereinafter, the present invention will be specifically described with reference to Examples, but it goes without saying that the present invention is not limited to these Examples.

Example 1 <Synthesis of 4- [2- (4-nitrophenyl) ethenyl] benzaldehyde> 10 ml of dimethylformamide (DMF) was added to 6.03 g (45 mmol) of terephthalaldehyde to form a solution. 2.72 g (15 mmol) of p-nitrophenylacetic acid was added to the solution.
About 40 ml of the MF solution was gradually added dropwise at room temperature while stirring.
Then, the temperature was raised to 100 ° C. in an oil bath, and the mixture was stirred for 2 hours. After allowing to cool, this solution was transferred to a separating funnel, and 150 ml of chloroform and 50 ml of 1N hydrochloric acid were added to carry out a liquid separation operation. The obtained chloroform layer was dried over anhydrous sodium sulfate, and then the solvent was distilled off. Water was added to the oily product and a yellow precipitate formed. The precipitate was filtered, washed with warm water and dried. The crude product was 3.06 g. The crude product was recrystallized from chloroform-methanol to obtain 2.54 g of the desired product.

The melting point of this compound was 218 to 220 ° C.

When the infrared absorption spectrum (IR) and the nuclear magnetic resonance absorption spectrum ( ¹ H-NMR) of this compound were measured, the characteristic spectrum was as follows, and the characteristic spectrum of 4- [2- (4-nitrophenyl) ethenyl] benzaldehyde was as follows: It was confirmed that it was obtained.

^{IR: 1690,1600,1500,1330,850 [cm -1] 1} H-NMR (CDC1 3): 10.1 (S, 1H), 8.53~7.60 (m, 8H),
7.37 (d, 2H) [δ (ppm)] Nd: Y was used as a fine powder crystal of 4- [2- (4-nitrophenyl) ethenyl] benzaldehyde obtained by the above synthesis.
When irradiated with an AG laser (wavelength = 1.064 μm, output 10 mJ / pulse), a second harmonic was generated (SHG), and green light with a wavelength half the incident light (532 nm) could be observed.

Further, the second harmonic generation (SHG) efficiency of the above-described microcrystals was 2.5, assuming that of urea was 1, and it was confirmed that the SHG efficiency is much stronger than that of urea.

Further, it was revealed that this crystal is stable at room temperature and has good crystallinity.

<Effects of the Invention> 4- [2- (4-nitrophenyl) ethenyl] of the present invention
Organic nonlinear optical materials composed of benzaldehyde form stable single crystals at room temperature and exhibit large SHG activity.
It can be used in a wide range of fields such as a light control element.

Claims (1)

[Claims] 1. The following general formula An organic nonlinear optical material characterized by comprising 4- [2- (4-nitrophenyl) ethenyl] benzaldehyde represented by: