JPH0381744A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain an excellent nonlinear optical material by incorporating m-bis(p-methyl styryl) benzene expressed by specific formula into the material. CONSTITUTION:m-Bis(p-methyl styryl) benzene expressed by the formula is incorporated into the nonlinear optical material. The compd. of this crystal has no symmetrical center and, therefore, exhibits a nonlinear optical effect. The efficiency of generating the second harmonic wave of the fine crystal powder is as high as the efficiency of generating the second harmonic wave of urea. The max. wavelength is 312nm and the cut-off wavelength is 360nm and exists in a short wavelength region. The crystal is stable at room temp., is hardly optically damaged, allows easy working, and has excellent white transparency. The compd. is usable as the nonlinear optical material in the form of powder, single crystal, soln., etc. The compd. is synthesized by bringing, for example, isophthal aldehyde and p-methyl benzyl triphenyl phosphonium salt into reaction in a solvent, such as dimethyl formamide, in the presence of a catalyst, such as sodium methoxide and lithium ethoxide.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to organic nonlinear materials used as optical control elements in a wide range of fields such as optical computers and optical communications. generation) m-bis(p-methylstyryl) with high activity, cutoff wavelength in the single wavelength range, white transparency, and good crystallinity.
Concerning organic nonlinear optical materials consisting of benzene.

[Conventional technology]

Nonlinear optical materials produce phenomena such as frequency conversion, amplification, oscillation, and switching of laser light, and generate second harmonics (
It can be applied to SHG), third harmonic generation (THG), high-speed shutter, optical memory, optical arithmetic element, etc. In addition, nonlinear optical materials can be applied to optical switches and the like that take advantage of the property that their refractive index changes depending on an electric field.

Conventionally, KH, PO, NH4H have been used as nonlinear optical materials.
Inorganic single crystal materials such as 2PO4, LiNbOx, and KNbOi are known, but recently urea, p-nitroaniline, 2-methyl-4-nitroaniline (MNA
), m-nitroaniline (mNA), 4- (N, N
-dimethylamino)-4'-nitrostilbene (DAN
Development of organic nonlinear optical materials such as S) is progressing.

Polymer materials such as polydiacetylene and polyvinylidene fluoride are also being considered for application to waveguides with control functions, optical ICs, etc. by utilizing their nonlinear optical effects.

Organic nonlinear optical materials generally have nonlinearity originating from intramolecular π electrons, so they do not involve lattice vibration in response to light, and therefore have faster response than inorganic materials. It is possible to synthesize a material whose absorption region can be changed. Moreover, the methods of making materials into devices are not limited to single crystallization, but also include LB film, vapor deposition, etc.
Various methods such as liquid crystal formation and polymerization are possible.

For recent research results on nonlinear optical materials, see e.g.
``Organic nonlinear optical materials'' supervised by Kato and Nakanishi (CM;
S CHEMLA, Spear, S CHEMLA, Published in 1985)
J, ZYSS m″Non1inear 0ptica
l Pro-perties and (:rysta
It is summarized in the literature ls'' Vol. I, Vol. II.

By the way, nonlinear optical materials are required to have the following characteristics.

(1) Among nonlinear optical effects, especially second harmonic generation (S
HG) is positioned as a basic technology for wavelength conversion due to its high conversion efficiency, and SHG efficiency (1
) is required.

(2) In order for a material to exhibit optical nonlinearity, it must not have spatial inversion symmetry, and in particular, its crystal must not have a center of symmetry.

(3) It is desired that the material be stable at room temperature and form a single crystal as large as possible.

(4) Since the wavelength of current semiconductor lasers is about 800 nm, it is practically desirable that the maximum wavelength (first ll1aX) and cutoff wavelength (λcutoff) be in the shortest wavelength region as possible.

However, known inorganic nonlinear optical materials are expensive to produce single crystals with high purity, have deliquescent properties, and are generally made of SHG.
It has the disadvantage of low efficiency.

On the other hand, although it is known that some organic nonlinear optical materials generally have high SHG efficiency, it is difficult to prepare stable and large crystals at room temperature. For example, MNA
Although it has high SHG efficiency, it is difficult to obtain large single crystals. Urea is easy to obtain large single crystals and has a white color.
Although it is transparent and has a short cutoff wavelength of 200 nm, it has the disadvantage of poor moisture resistance. Further, DANS, which is a stilbene derivative, exhibits a very large second-order nonlinear polarizability β at the molecular level, but when crystallized, the molecular arrangement has inversion symmetry and therefore does not exhibit a nonlinear optical effect.

In addition, organic nonlinear optical materials generally give yellow or yellow-orange colored crystals due to the structure of π-electron conjugation, and for this reason, the cutoff wavelength is usually 40°C.
It is located in a long wavelength region exceeding 0 nm. For example, p
- 470 nm for nitrosoaniline, 480 nm for MNA
For DANS, the cutoff wavelength exists in a considerably long wavelength region of 430 to 580 nm. Therefore, from the viewpoint of practical characteristics required for an optical frequency conversion element, it is required that the material be white and transparent, have a wide transparent wavelength range, and have a cutoff wavelength in a single wavelength range of 400 nm or less.

Recently, as organic nonlinear optical materials, various diolefin compounds (JP-A-61-78748), benzalacetophenone derivatives (JP-A-63-85526), N-[
A group of compounds including new compounds such as 2-(5-nitylofurylidene)]-]4-methoxyaniline (JP-A-63-96639) have been developed. However, it has high SHG efficiency, is stable, and is easy to grow into large single crystals.
Moreover, it is still insufficient to provide a nonlinear optical material with excellent transparency and a short cutoff wavelength.

[Problems to be Solved by the Invention] An object of the present invention is to overcome the problems of the prior art, form a single crystal that is stable at room temperature and does not have a center of symmetry,
Can be grown into large single crystals as needed,
The object of the present invention is to provide an organic nonlinear optical material that has high SHG activity, excellent transparency, and has a cutoff wavelength in a single wavelength region.

As a result of intensive research, the present inventors found that m-bis(p-methylstyryl)benzene, which is a diolefin compound and has a specific substituent and structure, forms white and transparent organic crystals with high SHG activity. Moreover, the cutoff wavelength is 360
It was discovered that the wavelength range is as short as nm, and the present invention was completed based on this knowledge.

[Means to solve the problem]

That is, according to the present invention, m represented by the following formula [I]
An organic nonlinear optical material is provided, characterized in that it is made of -bis(p-methylstyryl)benzene.

Hereinafter, the constituent elements of the present invention will be explained in detail.

[m-bis(p-methylstyryl)benzene] The compound used in the present invention, m-bis(p-methylstyryl)benzene, has no center of symmetry in its crystals, so it exhibits an excellent nonlinear optical effect and has a microcrystalline structure. The SHG efficiency of the powder is comparable to that of urea. Moreover, the max of the compound of the present invention is 312
nm and Lcutoff are in the short wavelength region of 360 nm.

As is clear from the above formula, the compound of the present invention has a structure in which two p-methylstyryl groups are bonded to the meta-position of benzene, which is the center of the π-electron conjugated chain. By having such a structure, the symmetry of the crystal is broken and at the same time polarization due to the methyl group remains, so it can be assumed that SHG activity is expressed.

The compound of the present invention has stable crystals at room temperature, is less susceptible to photodamage, and is easy to process, so it can be easily fabricated into devices. Crystals of this compound exhibit excellent nonlinear optical effects, as evidenced by the SHG efficiency comparable to that of urea. In addition, it has excellent white transparency,
Because the cutoff wavelength is 360 nm, which is in the single wavelength region,
It can be used as a wavelength conversion element for semiconductor lasers with a wavelength of about 800 nm.

The compound of the present invention can be used as a nonlinear optical material in various forms such as powder, single crystal, and solution.

(Production method) The m-bis(p-methylstyryl)benzene of the present invention is
For example, the known method for synthesizing 1,4-distyrylbenzene derivatives (CAMPBELL AND McDONALD
J.

Org, (:hm, 24.1246 (1959)). In this known synthesis method, a distyrylbenzene derivative represented by the general formula [II] is obtained in the -step using a bisphosphonium salt or terephthalaldehyde as a starting material.

The compounds of the invention can be used, for example, with isophthalaldehyde and p
-methylbenzyltriphenylphosphonium salt in an organic solvent such as dimethylformamide in the presence of a catalyst such as sodium methoxide or lithium ethoxide.

[Examples] The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

[Example 1] (1) Synthesis example of m-bis(p-methylstyryl)benzene 1.34 g (lommol) of isophthalaldehyde and 9.80 g (20 mmol) of p-methylbenzyltriphenylphosphonium bromide were mixed with 30 mI2 After adding dry dimethylformamide to form a solution, 20 mL of a methanol solution of 1.62 g (30 mmol) of sodium methoxide was slowly added dropwise under an argon stream.

After stirring this solution at room temperature for 4 hours, it was concentrated and an appropriate amount of ethanol was added. The precipitate was filtered and washed with methanol to obtain the target compound m-bis(p-methylstyryl)benzene. The yield was 1.6g.

Next, the results of measuring the IR, 'H-NMR, UV and melting point of the product are shown below.

Melting point: 208°C IR: 3100-2800 (CH-), 1600 (
Ar-C=C).

980 (C:C) [cm-1] H-NMR: 2.4 (S, 6H), 7.09 (d, 2H
, J=16.8) (CDIJj) 7.17 (d
, 4H, J=16.8), 7.21 (d, 4H.

J=8.1), 7.3-7.4 (Ill, 3H), 7
．． 46 (d.

4H, J=8.1), 7.65(s, IH) [δ(p
pm)] UV absorption: Max=312 nm.

(Etoul cutoff = 360 n
m From these analytical results, it is clear that this compound is m-bis(p
-Methystyryl)benzene.

Furthermore, it can be seen that the cutoff wavelength is 360 nm, which is in the short wavelength region.

(2) Confirmation experiment of nonlinear optical effect Nd: YAG laser (wavelength = 1.06
4 μm, output 10 mJ/pulse), the second harmonic is generated (SHG) l,, 1/2 wavelength of the incident light (
532 nm) green light could be observed. Also, its strength (
It was confirmed that the SHG efficiency) was comparable to that of urea.

It has been revealed that the crystals of this compound are stable at room temperature, have excellent resistance to light damage, have good crystallinity, and are white and transparent.

From the above facts, it can be seen that this compound is an excellent nonlinear optical material.

[Effects of the Invention] According to the present invention, SHG is stable at room temperature and has good crystallinity.
It is possible to provide an organic nonlinear material that has high activity, excellent transparency, and has a cutoff wavelength in a short wavelength region. The organic nonlinear optical material of the present invention has important practical significance, such as being able to be used as a wavelength conversion element for a semiconductor laser.

Claims (1)

[Claims] (1) An organic nonlinear optical material characterized by being composed of m-bis(p-methylstyryl)benzene represented by the following formula [I] ▲Mathematical formulas, chemical formulas, tables, etc.▼ [I].