JPH04235535A - Nonlinear optical material and light wavelength changing method using it - Google Patents

Abstract

PURPOSE:To exhibit high nonlinear responsiveness and to be excellent in blue light permeability by composing the material of a specific compound. CONSTITUTION:A compound expressed by the formula I is used as a nonlinear optical responsive compound. In the formula I an alkyl group represented by R<1> and R<2> has a carbon number of 1 to 24, preferably 1 to 10. An allyl group represented by R<1> and R<2> has a carbon number of 6 to 24, desirably 6 to 14, and more desirably 6 to 10. A methyne group represented by L<1> and L<2> may be substituted by an alkyl group or allyl group and desirably have a carbon number of 1 to 10 and more desirably 1 to 3: the most desirable carbon number thereof is 1, i.e., CH. One or more hydrogen atom of the compound may be substituted by heavey on hydrogen atom.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to compounds and molecular crystals useful as nonlinear optical materials. The present invention also relates to a method of converting optical wavelength using these materials as nonlinear optical materials.

0002

BACKGROUND OF THE INVENTION In recent years, nonlinear optical materials, which exhibit nonlinearity between polarization and electric field that appears when a strong optical electric field such as laser light is applied, have attracted attention. Such materials are generally known as nonlinear optical materials and are described in detail in, for example: “Nonlinear Optical Properties of Organic and Polymeric Materials” ACS Symposium Series 233 Edited by David Jay Williams (American Chemical Society 1983)
Annual) ``Nonlinear Optical Pr
operties of organic and p.
Olymeric Material” ACS SY
MPOSIUM SERIES 233 David
J. Edited by Williams (AmericanChem)
ical Society, published in 1983), "Organic Nonlinear Optical Materials" supervised by Masao Kato and Hachiro Nakanishi (CMC, published in 1985, "Nonlinear Optical Properties of Organic Molecules and Crystals") Volumes 1 and 2, edited by D. S. Shumura and J. Jisu (Academic Press, 1987) “Nonlinear
OpticalProperties of Or
ganic molecules and crystal
als” vol 1 and 2 D.S. Cheml
a and J. Edited by Zyss (Academic Pr.
(Published by ess).

One of the uses of nonlinear optical materials is second harmonic generation (SHG) based on second-order nonlinear effects and wavelength conversion devices using sum frequency and difference frequency. The materials that have been practically used so far are inorganic perovskites represented by lithium niobate. However, recently, it has become known that π-electron conjugated organic compounds having an electron-donating group and an electron-withdrawing group have various performances as nonlinear optical materials that far exceed those of the above-mentioned inorganic materials.

[0004]For the formation of higher performance nonlinear optical materials,
It is necessary to arrange compounds with high nonlinear susceptibility in the molecular state so as not to cause inversion symmetry. It is known that compounds with long π-electron conjugated chains are useful for expressing high nonlinear susceptibility, which is one of these, and are variously described in the above-mentioned literature, but in these compounds, As is obvious, the absorption maximum wavelength becomes longer, leading to a decrease in the transmittance of, for example, blue light, which becomes an obstacle to the generation of blue light as the second harmonic. This also occurs in p-nitroaniline derivatives, and the fact that the transmittance of that wavelength has a large influence on the efficiency of second harmonic generation is described in Aline Azema et al., Proceedings of the National Institutes of Science and Technology. 40
Volume 0, New Optical Materials (Alai
n Azems et al., Proceedings of
SPIE, Volume 400, Now Optical M
This is clear from Figure 4, p. 186, (1983). Therefore, the emergence of nonlinear optical materials with high transmittance for blue light is desired. Conventionally, attempts have been made to replace the carbon atoms in the benzene nucleus of nitroaniline with nitrogen atoms, but satisfactory results have not always been obtained.

[0005] The present applicant has also disclosed a better method in Japanese Patent Laid-Open Nos. 62-210430 and 62-21.
It was disclosed in Publication No. 0432. Furthermore, JP-A-62-59
No. 934, JP-A-63-23136, JP-A-63-2
6638, JP 63-31768, JP 63-
163827, JP 63-146025, JP 63-85526, JP 63-239427, JP 1-100521, JP 64-56425,
JP-A-1-102529, JP-A-1-102530, JP-A-1-237625, JP-A-1-207724
Many materials have been disclosed in publications such as the above.

However, as mentioned above, in order to be useful as a second-order nonlinear optical material, performance in the molecular state alone is insufficient, and the molecular arrangement in the aggregate state must have no inversion symmetry. is required. However, currently it is extremely difficult to predict the molecular arrangement, and the probability of its existence among all organic compounds is not high.

[0007] Furthermore, JP-A-63-221327 also discloses derivatives of cinnamic acid esters, but in this invention, the carbon atom to which the ester group is bonded has one more type of electron-attracting There is a description that it is preferable that a group, especially a cyano group, be bonded, and the compounds specifically shown are also limited to those included in this category. Therefore, all of the exemplified compounds are blue SHG
The absorption wavelength is too long to be used as an element, so it is not preferable.

[0008] Furthermore, when used as an element for wavelength conversion, it is necessary to give sufficient consideration to the arrangement of molecules in the crystal, but in many of the above methods, this point is not necessarily sufficiently taken into account. Furthermore, to date, no wavelength conversion element using an organic nonlinear optical material has appeared on the market as a commercial product.

[0009]

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide an organic nonlinear optical material that exhibits high nonlinear response and excellent blue light transmittance. The second object is to provide a molecular crystal that has excellent blue light transmittance and has a molecular arrangement without inversion symmetry. A third objective is to provide a method that utilizes the response related to optical wavelength conversion among nonlinear responses.

0010

[Means for Solving the Problems] As a result of extensive research, the present inventors have found that by using a compound represented by general formula (I) as a nonlinear optically responsive compound, and by using a compound represented by general formula (II), It has been found that the objects of the present invention can be achieved by a molecular crystal characterized in that it is constituted by the molecules represented.

[0011]

[Chemical formula 3]

0012

embedded image The compound of general formula (I) will be explained in more detail. R
The alkyl group represented by 1 and R2 has 1 to 24 carbon atoms, preferably 1 to 10 carbon atoms.
and more preferably one having 1 to 5 carbon atoms (for example, methyl, ethyl, propyl, i-propyl, butyl, i-butyl, sec-butyl, tert-butyl, pentyl, i, pentyl, sec-pentyl) ,t
ert-pentyl). Further, these may be substituted with, for example, a halogen atom, a hydroxy group, an alkoxy group, an aryl group, a carboxy group, an alkoxycarbonyl group, an amino group, or a cyano group. R1 and R
The aryl group represented by 2 has 6 to 24 carbon atoms, preferably 6 to 14 carbon atoms, and more preferably 6 to 10 carbon atoms (for example, phenyl, 1-naphthyl, and 2-naphthyl are listed). ). Also,
These may be substituted, for example, with the groups mentioned above and with alkyl groups. The methine group represented by L1 and L2 may be substituted with an alkyl group or an aryl group,
It preferably has 1 to 10 carbon atoms, and more preferably 1 to 3 carbon atoms. The most preferred is one carbon number, ie, CH. Further, one or more hydrogen atoms in this compound may be substituted with deuterium atoms.

Specific examples of the compounds represented by the general formula (I) are shown below.

[0014]

[C5]

These compounds can generally be easily synthesized by suitably etherifying or esterifying commercially available 4-hydroxycinnamic acid. Regarding the methods of etherification and esterification, the following books can be referred to. Stanley R.S.
andler, Wolf Karo) Organic Functional Group Preparations
roup Preparations) Academic
Academic Press 1968
Published annually Chapters 5 and 10 Edited by the Chemical Society of Japan, New Experimental Chemistry Course Maruzen Published 1977 Volume 14 Synthesis and Reactions of Organic Compounds [I] Chapter 3 Section 3 and [II] Chapter 5 Section 2

Next, as a representative example, the synthesis method for Compound Example 1 will be described. Synthesis Example-1 3.5 liters of methanol was added to a 5 liter three-necked flask equipped with a reflux condenser and a stirrer, and 489 g (2.98 mol) of 4-hydroxycinnamic acid was added thereto and dissolved by heating and stirring at 30°C. Next, 25 ml of concentrated sulfuric acid was added and the mixture was refluxed for 5 hours, and then cooled down to room temperature. The reaction mixture was diluted with NaHCO3
100 g of the solution was poured into a solution of 14 liters of water, and the precipitate formed was collected by filtration. The filtered precipitate was washed with water and dried,
-Hydroxycinnamic acid methyl ester 481g (2
．． 70 mol) was obtained. Yield: 90.6% Melting point: 139-140.5°C (recrystallized from methanol)

Synthesis Example 2 (Synthesis of Compound Example 9), 1 g of 4-hydroxycinnamic acid methyl ester obtained in Synthesis Example 1
was weighed into a 100 ml eggplant-shaped flask equipped with a reflux condenser, and 50 ml of methanol d4 was added. After heating under reflux for 4 hours, 40 ml of the solvent was distilled off. It was cooled on ice and the precipitated crystals were collected by filtration. Yield: 0.7 g (yield: 70%) Melting point: 138-141°C When 1H-nmr of this compound was measured, 90% of the hydrogen atoms in the hydroxyl groups were replaced with deuterium.

Next, the powder obtained here is made into a single crystal. Methods for single crystallization include solution methods such as the solvent evaporation method, temperature drop method, and vapor diffusion method, and Bridgman method. Examples include liquid dilution method and sublimation method. For single crystallization, please refer to "Crystal Engineering Handbook (Kyoritsu Shuppan, published 1971)" Volume VI, edited by the Crystal Engineering Handbook Editorial Committee.
This can be done by referring to the description in Part I, Chapter 8.

Methods of wavelength conversion include methods using a single crystal of an appropriate size and using angular phase matching or temperature phase matching, and methods using Cerenkov radiation using a waveguide. Examples of the laser light source used as the fundamental wave include those in Table 1. It should be noted that the wavelength of the fundamental wave is not limited in any way except for the influence of absorption of the material mentioned above. This is true for laser and optronics (Las
er & Optronics) page 59 (November 1987)
Monthly) is more obvious.

[0020]

[Table 1]

[0021]

EXAMPLES Next, the present invention will be explained in more detail based on Examples, but the present invention is not limited thereto. Example 1 The 4-hydroxycinnamic acid methyl ester obtained in Synthesis Example 1 was made into a chloroform solution, and colorless prism crystals were obtained by a solvent evaporation method. X-ray crystal structure analysis was performed using this crystal. The results are shown below. Crystallographic data Monoclinic system, space group Cc Lattice constant a = 20.304 Å b = 7.123 Å
c=6.291Åα=90.00° β=9
5.85° γ = 90.00° Number of molecules per unit cell Z = 4 The crystal structure diagram is shown in Figure 1. From the space group of the crystallographic data above, it can be seen that this crystal does not have inversion symmetry.

Example 2 The single crystal obtained in Example 1 was powdered in an agate mortar, and the second harmonic generation was measured by S.K.
urtz), T.T.Perry
This was carried out according to the method described in J. Appl. Phys., Vol. 39, p. 3798 (published in 1968). The measurement was performed using the apparatus shown in FIG. That is, the measurement was performed using pulsed YAG laser light (λ=1.06
4μm, beam diameter≒1mmφ, peak power≒10Mw
/cm2) was used as the fundamental wave, and the intensity of its second harmonic was measured using the evaluation device shown in FIG. The measurement was performed by relative comparison with the intensity of the second harmonic of urea. In addition, when the intensity was weak, visual observation was performed. In particular, in order to distinguish between light emission due to two-photon absorption of the fundamental wave (mainly yellow and red light emission) and second harmonics, a spectrometer was installed to measure only the second harmonics. Furthermore, the main purpose of powder method measurement is to determine the presence or absence of nonlinearity in the substance, and the intensity ratio is a reference value for the magnitude of specific linearity. The results are shown in Table 2.

[0023]

[Table 2]

[0024]

[C6]

Therefore, it is clear that the compound of the present invention has excellent blue light transmittance and is capable of wavelength conversion.

Example 3 Using the crystal obtained in Synthesis Example 2, the second harmonic was measured in the same manner as in Example 2. It was possible to visually observe the green second harmonic.

[0027]

[Effects of the Invention] The compound of the present invention has high blue light transmittance and is capable of wavelength conversion, so it is a useful material for a wavelength conversion element for generating blue light.

[0028]

[Brief explanation of the drawing]

[0029]

[Figure 1]

[0030] FIG. 2 is a stereogram obtained from X-ray crystal structure analysis in Example 1.

[0031]

[Figure 2]

This is the second harmonic generation measuring device used in Example 2.

[0033]

[Explanation of symbols]

1 Powder sample 2 Fundamental wave cut filter 3 Spectrometer 4 Photomaru 5 Amplifier 6 Wavelength 1.064μm 7 0.532μm

Claims (4)

[Claims] 1. A nonlinear optical material comprising a compound represented by the following general formula (I). In the general formula (I), R1 and R2 represent a hydrogen atom, an alkyl group having 1 to 24 carbon atoms, or an aryl group having 6 to 24 carbon atoms. L1 and L2 represent methine groups. [Chemical formula 1] 2. The compound according to claim 1, wherein at least one hydrogen atom is replaced with a deuterium atom.
Nonlinear optical materials. 3. A nonlinear optical material consisting of a monoclinic molecular crystal having a space group of Cc, characterized in that it is constituted by molecules represented by the following general formula (II). General formula (II) [Chemical formula 2] 4. A method of converting a light wavelength using the nonlinear optical material according to claim 1 or 2 when converting a light wavelength using a laser beam and a nonlinear optical material.