JPH0339727A - Nonlinear optical material - Google Patents

Abstract

PURPOSE:To make it possible to form a crystal having high hypermolecular polarizability beta and free from the center of reflection symmetry by using a nonlinear optical material made of specified N,N'-bis-(ethoxycarbonylphenyl)- methanediamine. CONSTITUTION:A nonlinear optical material made of N,N'- bis-(ethoxycarbonylphenyl)-methanediamine represented by formula I is used. The methanediamine represented by the formula I may be obtd. by dissolving ethyl aminobenzoate in a solvent having high solvent power such as methanol, ethanol, methyl ethyl ketone or methyl isobutyl ketone and by allowing the resulting reactive soln. of a specified pH to react with formaldehyde. A high quality crystal having high hypermolecular polarizability beta as a molecule and free from the center of reflection symmetry is easily obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an organic nonlinear optical material that has a large supramolecular polarizability β and can form a crystal without a center of inversion symmetry.

[Conventional technology]

A nonlinear optical effect is a phenomenon in which when extremely strong light passes through an object, the material is polarized by the electric field of the light, and this induced polarization generates optical harmonics and changes the incident light itself.

This phenomenon was known before the invention of lasers, but it came into focus with the advent of laser light. In particular, optical harmonic generation, optical parametric oscillation and amplification, which have recently attracted attention for application to optical functional devices,
The discovery of phenomena such as optical phase conjugation and optical bistability owes much to the invention of lasers.
Applications include optical modulation and distortion-free transmission of optical signals. Therefore, nonlinear optical effect elements are positioned as functional materials that hold the key to the fields of optical information processing and optical communication, which will continue to be in increasing demand.

Conventionally, substances that exhibit nonlinear optical effects include, for example, potassium dihydrogen phosphate (KDP) and lithium niobate (L
iNbO3), β-barium borate (BBO), etc. have been studied, and some have been put into practical use as element materials.However, substances that exhibit nonlinear optical effects are not limited to inorganic dielectric compounds, but also organic compounds. It is also found in Moreover, the nonlinear optical action of organic compounds is caused by the movement of π electrons that are delocalized within the molecule, so compared to the σ electrons of inorganic dielectrics, which are strongly bound to the nucleus and have restrictions on lattice vibration, the induced polarization is It's vaguely fast and big, actually.
2-Methyl-4-nitroaniline (MNA) exhibits a figure of merit more than 2000 times that of lithium niobate (B, F
, LI! -VINE et al, J, App
ly, Phys, Vol. 50, 2523 (1979
〉〕.

For this reason, practical research on second-order nonlinear optical effects, especially optical second harmonic generation (SHG), which is expected to be the earliest to be applied as optical functional elements among nonlinear optical effects, has focused on organic compounds. For example, MNA (Japanese Patent Application Laid-Open No. 55-500960), nitropyridine-1-oxide derivatives, JP-A No. 56-928
Materials such as those disclosed in Japanese Patent No. 70 and Japanese Patent No. 56-94333 have already been proposed as nonlinear optical materials.

[Problem to be solved by the invention] In order to enhance the second-order nonlinear optical effect in organic compounds, it is sufficient to increase the dipole moment of the molecule. It is well known that it is effective to introduce

However, important unresolved issues remain in this regard. In other words, it must be a crystal without a center of inversion symmetry. However, when organic compounds that have a large dipole moment in their molecules are arranged so that their dipole moments cancel each other out when they crystallize, the molecules have a large second-order supramolecular polarizability β but are crystallized or As a molecular assembly, it may not exhibit second-order nonlinear optical effects because it has a center of inversion symmetry. In fact, there are a large number of such organic compounds.

Therefore, when developing an organic nonlinear optical material that focuses on second-order nonlinear optical effects, it is necessary to develop a compound that has a large supramolecular polarizability β as a molecule and from which high-quality crystals with no center of inversion symmetry can be easily obtained. Synthesis is an important issue.

4-Nitroaniline is an aromatic compound with the simplest electron-donating group and electron-withdrawing group, and is one of the compounds with a large supramolecular polarizability β among organic compounds.
The crystal has a center of inversion symmetry because the molecules are arranged so that their dipole moments cancel each other out, and it does not exhibit second-order nonlinear optical effects.

Furthermore, due to intramolecular charge transfer due to nitro groups and amino groups, large electronic transition absorption exists in the visible range from outside myopia.

For this reason, 4-nitroaniline is significantly colored.

The present inventors have conducted intensive studies on improving the symmetry and transparency of aromatic compounds such as 4-nitroaniline, which have an electron-withdrawing group and an electron-donating group at the rose position of the benzene ring. We developed the present invention after confirming that certain benzoic acid derivatives do not have a center of inversion symmetry when they form crystals or molecular aggregates, and that they can significantly improve transparency in the visible range beyond myopia. This is what we have come to.

The purpose of the present invention is to develop a nonlinear optical material derived from benzoic acid with an intramolecular charge transfer structure, which has a large supramolecular polarizability β, and which is capable of forming crystals without an inversion symmetry center, and to further expand the usable wavelength range. The objective is to provide a nonlinear optical material with a shortened cutoff wavelength in order to achieve this goal.

[Means to solve the problem]

The nonlinear optical material according to the present invention for achieving the above object is characterized in that it consists of N,N'-bis-(ethoxycarbonylphenyl>-methanediamine) represented by the following chemical formula.

N,N'-bis-(ethoxycarbonylphenyl)-methanediamine of the above chemical formula can be obtained, for example, by reacting ethyl aminobenzoate with formaldehyde after selecting the reaction solvent and the pH of the reaction solution. I can do it.

This involves reacting with formaldehyde using a highly soluble solvent such as methanol, ethanol, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, or dimethyl formamide.

When the obtained Hl-bis-(ethoxycarbonylphenyl)-methanesyanin is irradiated with a Nd n YAG laser (λ-1064m5+) in a powder state, it generates a significantly strong green second harmonic. In this state, phase matching is possible over a wide range and generates second harmonics with an intensity that slightly exceeds that of powder.

Generally, the propagation constants of the fundamental wave and harmonics in a crystal do not match, so it is difficult to generate harmonics in the crystal state.

This matching is called phase matching, and unless this phase matching is achieved, it is not possible to observe the generation of harmonics.

In addition, it is white in the powder state and colorless and transparent in the single crystal state, and the cutoff wavelength is significantly shifted to a single wavelength.

When the fundamental wave is infrared light of 1 to 1.2n, the fundamental wave may be absorbed overlapping with the overtone absorption of the C-H stretching vibration and converted into thermal vibration. Therefore, when the intensity of the fundamental wave is strong, the temperature of the crystal rises and the phase matching conditions change or the angle of the emitted light changes.

In the present invention, when the hydrogen of an alkyl group with particularly large overtone absorption is replaced with deuterium, the absorption region shifts to the longer wavelength side, and this phenomenon can be effectively prevented.

[For production]

According to the present invention, by connecting ethyl aminobenzoate, which has a strong tendency to form crystals with a center of inversion symmetry due to its large dipole moment, with a methylene bond, the symmetry is reduced and a second-order nonlinear optical effect is produced in a wide wavelength range. Provided is a nonlinear optical material with novel physical properties that has been converted into a material that is active against.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

Example 1 Ethyl 4-aminobenzoate 7.63g (50msol)
was dissolved in methanol loo*I, and in this solution, 10 g of formaldehyde (37χ) aqueous solution was dissolved in methanol 20
After the completion of the 0 reaction, the concentrated and precipitated reactant was separated from the furnace, and methanol 2
After washing three times at 0ml, dry at 50°C under reduced pressure with N.

N'-bis-(4-ethoxycarbonylphenyl)-methanediamine was obtained.

The cutoff wavelength of this N,N'-bis-<4-ethoxycarbonylphenyl>-methanediamine was measured and was found to be 330 mm.

Additionally, a Q-switched Nd:YAG laser (λ”
When irradiated with a 10 nsec pulse using 101064n, the S H0 intensity was 30 times that of urea (powder method).

Example 2 In Example 1, deuterium-substituted N,N'-bis-(methoxycarbonylphenyl)-ethanediamine was synthesized using deuterated formaldehyde instead of formaldehyde and salt methanol instead of methanol.

Example 3 N,N'-bis-(4-ethoxycarbonylphenyl)
- 2 g of methanediamine was made into a saturated solution of tetrahydrofuran, and the temperature was kept constant at 25° C., and crystal growth was performed for 2 days by the solvent evaporation method to obtain rod-shaped crystals of 1 ml, 1 m, and 20 sn.

This crystal has a Q-switched Nd:YAG laser (λ”
' When irradiated with a 1onsec pulse using 101064ri, phase matching was possible, and SHG in the powder state
SHO was obtained in transmitted light with an intensity far exceeding the intensity.

〔Effect of the invention〕

As described above, the nonlinear optical material of the present invention made of N,N'-bis-(ethoxycarbonylphenyl)-methanediamine exhibited SHG efficiency 30 times higher than that of urea, and phase matching was possible in the crystalline state. .

Furthermore, in existing nonlinear materials such as MNA that have large nonlinear optical effects, the cutoff wavelength generally extends to the long wavelength range (MNA: 48 Onm), which limits the range of use as nonlinear optical materials, especially wavelength conversion materials. However, N,N'-bis(ethoxycarbonylphenyl)-methanediamine according to the present invention has a cutoff wavelength of 33 On-, and can be used in a wide wavelength range.

Therefore, various uses can be expected in a wide wavelength range as materials for various optical aperture elements that utilize nonlinear optical effects and electro-optic effects, such as wavelength conversion elements and light control elements.

Claims (1)

[Claims] 1. A nonlinear optical material comprising N,N'-bis-(ethoxycarbonylphenyl)-methanediamine represented by the following chemical formula. ▲Contains mathematical formulas, chemical formulas, tables, etc.▼