JPH01173017A - Organic second order non-linear optical material - Google Patents

Abstract

PURPOSE:To obtain a large second order non-linear optical effect, and also, to raise the preservation stability by allowing the title material to have a large optical non-linearity consisting of a stilbene derivative. CONSTITUTION:The title material consists of a stilbene derivative shown by formula I, and has a large non-linearity of >=10 times of urea. In the formula I, D, A and R<1>-R<4> denote a Hammett's substituent constant sigmap and a donor property substituent selected from 0.2>=sigmap>-0.4 halogen, a Hammett's substitu ent constant sigmap and an acceptor property substituent selected from sigmaps>0.2, and hydrogen or arbitrary substituents, at least one of which is an asymmetrical substituent which has been led into an asymmetrical part, respectively. As a result, the center symmetric property in a bulk state, for instance, in a crystal state is broken down, and also, it is brought to orientation control to a bulk structure which can utilize a secondary optical non-linearity which a molecular has, and a large secondary non-linear optical effect can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a second-order nonlinear optical material 1 used in fields such as optical information processing and optical communication. More specifically, the present invention relates to an organic compound having a large second-order nonlinear optical effect and excellent storage stability.

[Prior Art] In the field of optoelectronics, materials that have a large nonlinear optical effect and respond at high speed have been discovered, and it is eagerly awaited to realize higher performance or nonlinear optical elements that have not been possible in the past. Therefore, many exploratory research efforts have been made to the detriment of developing such high-performance materials. Conventionally, inorganic materials have been the main target of exploration, but no material satisfying the above requirements has been found. Therefore, in recent years, π is expected to have a large nonlinear optical effect and a fast optical response in principle.
Organic compounds with electronic conjugated systems have attracted attention.

Organic materials with second-order nonlinear optical effects have already been actively studied in various compound systems, and there are many general explanations (AC3 symposium).
5eries 233 (1983); D, J, Wi
Williams Angew, Chem, Int, Ed
, Engl., 23 p690 (1984), etc.).

Representative materials developed to date include, for example, N-(
4-nitrophenyl)-1-prolinol (NPP) [
JP-A-59-21665], N-[5-(2-nitropyridyl)]-]L-prolinol PNP) and 2-acedelamino-4-nitro-N,N-dimethylaniline (DAN). benzene and pyridine derivatives, stilbazoliums such as 4'-dimethylamino-N-methyl-4-stilbazolium methosulfate (DMSM), and 4-ditropenezylidene-4-(
N,N-dimethyl)aniline, 4-m:trobenzylidene-4-methylaniline (PrOCeedings (T
rudy) of the P,N,Levedeb
Physics Institute, Vol 9B (
1982), Ba5ov, N.G., Editor (Co.
nsultants BtJrealJ :New
York, N, Y, ) shigortn, v, op
77: “HaterialS and Apparat
tjS in QuantUIIIRadiOPhys
ics”), 4=-methylbenzylidene-4=
Examples include benzylideneaniline derivatives such as nitroaniline.

The nonlinear optical effect of organic compounds having a π-electron conjugated system is said to be caused by the fluctuation of π-electrons upon incidence of laser light. Therefore, in order to increase this fluctuation, substituents having donor properties and acceptor properties are introduced into the π-electron conjugated system, as shown in the above representative material examples.

In general, the crystal structure of an organic compound is determined by the structure of each molecule and intermolecular cohesive forces such as hydrogen bonding during backing, Van-der-Waa, Luss interactions, and dipole-dipole interactions.

When a combination of substituents with strong donor and acceptor properties, such as an amino group and a nitro group, is introduced into a π-electron conjugated system, the dipole moment of the molecule increases, and the dipole-dipole interaction between molecules during crystal formation increases. The effect becomes stronger. Such compounds have two
It tends to form centrosymmetric crystals, a structure in which the dipoles of the molecules cancel each other out.

However, such a centrosymmetric crystal does not exhibit second-order nonlinear optical effects.

In conventional research, in order to break the central symmetry of the crystal, which is a problem in expressing the second-order nonlinear optical effect in the crystal state,
Efforts have been made to introduce substituents, particularly optically active substituents and substituents with a high ability to form hydrogen bonds, at asymmetric positions in the molecule, and there have been successful examples of this in the case of benzene and pyridine derivatives. Representative examples include NPP, PNP, and DAN. However, it has been reported that, for example, NPP has achieved the optimum molecular orientation for producing a second-order nonlinear optical effect, and the magnitude of the second-order nonlinear optical effect is at most 150 times that of urea. Therefore, when trying to develop a material that has a larger second-order nonlinear optical effect than NPP, benzene is recommended.

Higher second-order hyperpolarizability than pyridine derivatives (two-dimensional hyperpolarizability of the molecule)
It was necessary to achieve non-centrosymmetric crystal grooves and appropriate molecular orientation in a compound with a structure that has second-order optical nonlinearity, which first appears in non-centrosymmetric crystals.

However, in compounds such as stilbene derivatives, which have a long π-electron conjugated system as a parent skeleton that has an order of magnitude higher second-order hyperpolarizability than benzene derivatives (e.g., p-nitroaniline), the dipole moment also changes accordingly. This is due to the fact that the central symmetry of the crystal cannot be broken, or even if it can be made non-centrosymmetric, it is not possible to achieve an appropriate molecular orientation to greatly express the second-order nonlinear optical effect. Contrary to expectations, only 1q of small second-order nonlinear optical effects were observed, which is less than that of benzene derivatives.

Therefore, in order to break the central symmetry of the crystal of a compound that has a long π-electron conjugated system as a parent skeleton and achieve an appropriate molecular orientation,
There is an example of considering the introduction of a salt structure with large steric hindrance. 2
A typical example is DMSM, which has a large hyperpolarizability and can exhibit a large second-order nonlinear optical effect by controlling the non-centrosymmetric crystal structure with the steric hindrance of the counter anion.

However, the salt structure of these compounds brings about properties that are undesirable as nonlinear optical materials, such as hygroscopicity and crystalline polymorphism, so problems remain in terms of storage stability and processability.

Stilbene derivatives with a long π-electron conjugated system as a parent skeleton that can increase second-order hyperpolarizability by introducing donor and acceptor substituents do not have the problems seen in DMSM, and exhibit large second-order nonlinearity in the crystalline state. It is expected that materials that exhibit optical effects will be obtained, but so far, N
There are no examples of success exceeding PP.

[Problems to be Solved by the Invention] An object of the present invention is to solve the problem that it is difficult to form a non-centrosymmetric structure in a stilbene derivative due to its large dipole moment. An object of the present invention is to provide an organic nonlinear optical material that exhibits a large second-order nonlinear optical effect by taking advantage of the hyperpolarizability of , and has excellent storage stability.

That is, the present inventors added a donor substituent at the 4-position,
It was confirmed through quantum chemical calculations that stilbene derivatives with an acceptor substituent introduced at the '-position can have large second-order hyperpolarizability.

Based on this knowledge, it was demonstrated that by introducing an asymmetric substituent into the asymmetric site of the phenyl group substituted with the donor group of a stilbene derivative, an organic secondary nonlinear optical material that exhibits large optical nonlinearity could be obtained. This led to the present invention.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

"An organic secondary nonlinear optical material comprising a stilbene derivative represented by the following general formula [1] and having optical nonlinearity 10 times or more greater than that of urea.

[However, D = Hammett's substituent constant σp, 0.2≧
Donor substituent selected from σp>-0,4 or halogen, A: Acceptor substituent selected from σp>0.2 with Hammett's substituent constant σp, R1 to R4: Hydrogen or any substituent and
At least one represents an asymmetric substituent introduced at an asymmetric site. ] The stilbene derivative as referred to in the present invention has a donor substituent selected from Hammett's substituent constant σp of 0.2≧σp >−0°4 or halogen at the 4-position, and σp＞
A phenyl group in which the donor group is substituted with an acceptor substituent selected from 0.2 at the 4-1 position and an asymmetric substituent having the effect of facilitating the formation of at least one non-centrosymmetric crystal. Right to the asymmetrical area.

That is, the features of the present invention are as follows: (1) A stilbene derivative with large hyperpolarizability was selected as the π-electron conjugated system.

■ The combination of donor and acceptor substituents is selected to provide a dipole moment size that allows for control of molecular orientation. In addition, ■ introducing an asymmetric substituent into an asymmetric site;

(Therefore, the bulk state, e.g. crystalline state)
The central symmetry of the molecule is broken, and the second-order optical nonlinearity of the molecule is utilized to control the orientation into a 1q bulk structure, making it possible to produce a large second-order nonlinear optical effect.

As shown in Comparative Example 1.2, it is difficult to stably form a crystal that exhibits a large second-order nonlinear optical effect only by making improvements. By applying a rough idea (■), we succeeded in making it easier to form a crystal that exhibits a large second-order nonlinear optical effect.

Furthermore, in this case, the intermolecular cohesive force is generally stronger compared to benzene derivatives and the like due to the π-electron interaction. That is, since the sublimation property and the water absorption property are also low, the storage stability in the bulk state is good. Table 3 shows known examples of NPP
, PNP, and DAN, the solubility of the material of the present invention in water was compared.

From the viewpoint of the above-mentioned good storage stability and high-speed photoresponsiveness, which is a characteristic of organic materials, among the materials within the scope of the present invention, the magnitude of the second-order nonlinear optical effect itself is urea ratio 10, that is, compared to conventionally used materials. Even materials as large as inorganic materials such as lithium niobate can be used depending on the purpose.

Examples of donor substituents in the present invention include hydroxyl groups, alkoxy groups such as methoxy, ethoxy, and phenoxy, human O-oxyalkyl groups such as hydroxymethyl and hydroxyethyl, and linear or branched alkyl groups, alkylsilyl groups such as trimethylsilyl, mercaptoalkyl groups such as mercaptomethyl, alkanoylamino groups such as acetylamino groups, and as acceptor substituents,
Nitro group, alkylsulfonyl group such as methylsulfonyl, cyano group, sulfamoyl group, alkylsulfamoyl group such as methylsulfamoyl, trifluoromethyl group, formyl, acyl group such as acetyl, trifluoromercaptomethylinyl group, Examples include a carboxy group, an alkoxycarbonyl group such as methoxycarbonyl and ethoxycarbonyl, a carbamoyl group, an alkylcarbamoyl group such as methylcarbamoyl, a trifluoromethoxy group, and a halogen. Halogen has both donor and acceptor properties, so it falls into both categories.

It is particularly preferable to introduce a nitro group as an acceptor substituent in order to improve the optical nonlinearity of the compound. In addition, when introducing a nitro group as an acceptor substituent, introducing a hydroxyl group or an alkoxy group as a donor substituent prevents the absorption from becoming longer wavelength, and also prevents the dipole moment of the molecule from becoming too large. preferable.

Asymmetric substituents are used to control the orientation of molecules in the bulk structure so that they are suitable for producing second-order nonlinear optical effects, and are substituents that have intermolecular forces that can change the bulk structure in the molecular backing. It is the basis. In other words, it is a group that breaks the central symmetry of both the molecule itself and the crystal as a whole, and controls the orientation into a bulk structure that can take advantage of the second-order optical nonlinearity of the molecule. A sterically hindered substituent or a hydrogen bond-forming substituent has a strong ability to change such backing, and is therefore particularly effective as the asymmetric substituent referred to in the present invention.

Any asymmetric substituent mentioned above may be used as long as it does not significantly affect the electronic state of the molecule.

However, unnecessarily large substituents are not preferable because they lead to a decrease in the molecule (matrix skeleton) density per unit volume and reduce the second-order nonlinear optical effect of the material. In the examples, methoxy, ethoxy, and methyl groups are used as sterically hindering substituents of appropriate size.

Furthermore, for the same reason, it is desirable that the number of asymmetric substituents be small. Therefore, preferably three of R1 to R4 are hydrogen.

In the present invention, it has also been found that a sufficient effect can be obtained by simply introducing one asymmetric substituent into a phenyl group into which a donor substituent has been introduced.

In this case, the ortho position of the donor substituent is particularly effective. This substitution position does not have a large effect on the electronic state of the molecule, and the degree of freedom in selecting a substituent that can be used as an asymmetric substituent is increased.

The compound of the present invention can be obtained by a general method for synthesizing dirubene compounds, which involves heating, dehydrating, decarboxylating, and condensing aldehyde and phenylacetic acid derivatives in the presence of a base catalyst (for example, piperidine).

Deuterated compounds have the effect of increasing transparency in the near-infrared region, but have nonlinear optical effects equivalent to non-deuterated compounds. Therefore, the above nonlinear optical compound is
Some or all of the hydrogens may be replaced with deuterium.

Examples of usage modes of the compound of the present invention include bulk single crystals and thin film single crystals. As a method for producing the single crystal, a solution method, a gas phase method, and a melting method can be applied. For example, for 4-methoxy-3-methyl-4'-nitrostilbene (MMNS) in Example 3, it is possible to produce a bulk single crystal by a solution method as shown in the example, and It is also possible to produce a thin film single crystal based on vapor phase growth such as slow melt cooling, vapor deposition on a substrate, or sublimation.

Bulk single crystals, thin film single crystals, etc. produced in this way can be used for nonlinear optical elements such as wavelength conversion elements, parametric oscillators, and optical switches, and for optical information processing using them.
It is useful for constructing optical communication systems.

[Examples] Hereinafter, the present invention will be explained in more detail using Examples, but the effectiveness of the present invention is not limited in any way by these Examples.

Example 1 4-Hydroxy-3-methoxy-4'-nitrostilbene (HMNS).

[Synthesis] 100 equipped with a reflux condenser and a magnetic stirrer
ml of 3-methoxy-4 in a three-meter flask, 4.560 (30 mmol
- hydroxybenzaldehyde (vanillin), 5.4
Add 3 g (30 mmo I > (7) p-nitro:)-diyl acetic acid, add about 18 ml of piperidine, and bring the oil temperature to about 12
The mixture was heated rapidly at 0° C. with stirring for about 8 hours.

The reaction solution turned red-black.

When Shun confirmed the completion of the reaction using thin layer chromatography using chloroform as the developing solvent, he stopped stirring.

When piperidine is removed using a rotary evaporator, a tar-like substance remains, but this is dissolved in acetone, the red fraction near the tip is collected using a silica gel chromatograph using chloroform as the developing solvent, and the solvent is removed using a rotary evaporator. Orange crude crystals were obtained. When the crude crystals were re-crystallized with acetonitrile, orange angular crystals were obtained, which were filtered and vacuum-dried.

[Target product 4.98Q (yield 61.3%) Melting point 179
．． 5-180.5°C] Identification was performed by IR and elemental analysis (see Table 2).

(IR: KBr tablet method cm-1) 3430 (OH): 2855 (-0CHz): 16
36.970 (-CH=CH-): 1506-15
18.1328 (-NO2): 1250°103
0(0CH3) Next, in order to investigate the magnitude of the second-order nonlinear optical effect of this compound, second harmonic generation (SHG) was performed using a powder method (S, T, T, Perry, J, A
ppl, Phys 39379B (1966)). The light source used for the measurement was a Nd:YAG laser (wavelength: 1.064 μm), and the sample I was ground to about 100 μm in a mortar. Laser irradiation conditions are pulse width 2 Q Q n5eC, repetition 10H.
2. Conducted at a peak power density of 30 MW/air.

The measurement results are shown in Table 1. HMNS according to the present invention has a SHG that is 70 times larger than that of the standard known compound urea.
showed that.

Further, when the solubility in water was examined, the HMNS according to the present invention was found to be substantially insoluble (see Table 3).

Example 2 3-Ethoxy-4-hydroxy-4'-nitrostilbene (HENS).

[Synthesis] 4.980 (30 mmol) of 3-ethoxy-4
-Hydroxybenzaldehyde and p-nitrophenylacetic acid of 5.43G (30 mmo I>) were used, but the reaction and separation and purification were carried out in exactly the same manner as in Example 1.

When the orange crude crystals were recrystallized with acetonitrile, 1 q of yellow-orange needle-like crystals (approximately 7 x 5 x 3 M) were obtained, which were filtered and vacuum-dried.

[Target product 5.90g (yield 68.9%) Melting point 161~
b Identification was performed by IR and elemental analysis (see Table 2).

(IR: KBr tablet method cm-') 3430 (-OH): 1 632. 9
70 (-CH=CI-1-): 1502-1506
．． 1325 (-NO2): 1 43B (-
00 days > CH3): 1 250, 1030 (
-0021-(5) Next, Table 1 shows the SHG measurement results of this compound. HENS according to the invention exhibited 30 times more SHG than the standard known compound urea.

Further, when the solubility in water was examined, HENS according to the present invention was found to be substantially insoluble (see Table 3).

Example 3 4-methoxy-3-methyl-4'-nitrostilbene (
MMNS).

[Synthesis] 6.03g (33mmol I) of 3-methy/l/-p
- anisaldehyde and 5.97 l (33 mmol l
) p-nitrophenylacetic acid and about 5 ml of piperidine were used, but the reaction was carried out in exactly the same manner as in Example 1.

The orange-red fraction near the tip of the resulting red tar-like substance was collected using a silica gel chromatograph using benzene as a developing solvent, and the solvent was removed using a rotary evaporator to obtain a yellow-orange oil. When this was crystallized with acetonitrile, yellow lumpy crystals were obtained, which were filtered and dried under vacuum.

[Target product 7.12Q (yield 80.2%) melting point] 1] ~
Identification was performed by IR and elemental analysis (see Table 2).

(IR: KBr tablet method cm-') 2960.2865 (-CH3); 2B50(-0
Cf-h): 1 635. 967 (-
CH=CH-): 1503.1320 (-NO2):
1450°1470 (-0CI-h, 20H3): 1
240,1024(-0CH3) When 5q of MMNS is dissolved in 5qml of acetonitrile while hot, allowed to cool, and crystallized by solvent evaporation method at room temperature, 1
A yellow mass of crystals measuring 1 x 1 x 1 cm was obtained. Observation with a polarized light microscope revealed that this crystal was a single crystal.

Next, Table 1 shows the measurement results of 5t-IG of this compound. MMNS according to the present invention exhibited an extremely large SHG of 650 times that of urea, a standard known compound, or about 4 times that of NPP, which exhibits the highest SHG among known materials. Figure 1 shows the relationship between powder particle size and SHG strength.

It was found that MMNS is phase consistent.

Further, when the solubility in water was examined, the MMNS according to the present invention was found to be substantially insoluble (see Table 3).

Comparative example 1 4-Hydroxy-4'-nitrostilbene.

(Synthesis) 3.66 g (30 mmol > (7) p-hydroxybenzaldehyde and 5.430 (30 mmol >
The reaction and separation and purification were carried out in exactly the same manner as in Example 1, except that p-nitrophenylacetic acid was used.

When the orange crude crystals were recrystallized with chloroform, yellow-orange angular crystals were obtained, which were filtered and dried under vacuum.

[Target product 4.33g (yield 65.3%) Melting point 209~
b Identification was performed by IR and elemental analysis (see Table 2).

(IR: KBr tablet method cm-') 3440 (-0H): 1630. 9
65 (-CH=CH-):1502,132B (
-NO2) Next, the SHG measurement results of this compound are shown in Table 1.
Shown below. HNS exhibited only 0.7 times as much SHG as the standard known compound, urea.

When the solubility in water was examined, HNS was found to be substantially insoluble (see Table 3).

Comparative example 2 4-Methoxy-4'-nitrostilbene (MNS).

[Synthesis] The reaction and separation and purification were carried out in the same manner as in Example 3, except that p-anisaldehyde of 4.080 (30 mmo I >) and p-nitrophenylacetic acid of 5.43 (J (30 mmo I >) were used. I did it.

When the yellow crude crystals were recrystallized with acetone, yellow-orange plate crystals were obtained. This was collected by filtration and vacuum dried.

[Target object 6.35CI (Yield 83.0%) Melting point 13
4-b When MNS is recrystallized with benzene, 1q of yellow plate crystals are obtained.
It was done.

Identification was performed by IR and elemental analysis (see Table 2).

(IR: KBr tablet method cm-1) 2830 (-0CHx): 1628.960 (-C
H=CH-): 1 500-1510.13
25(-NO2) Next, Table 1 shows the SHG measurement results of this compound. MNS recrystallized with acetone showed only the same level of SHG as the standard known material urea. On the other hand, MNS recrystallized with benzene showed 67 times more SHG than urea.

FIG. 2 shows the results of powder X-ray analysis of these two types of MNS crystals. The phenomenon of "crystal polymorphism" was confirmed, leaving concerns about the ability to produce stable crystals with large second-order nonlinear optical effects.

When the solubility in water was examined, MNS was found to be substantially insoluble (see Table 3).

Table 20 Elements of synthetic organic nonlinear optical compounds (CI-IN)
Analysis result shows less than Q/100m1.

However, the measurement temperature was 25°C.

[Effects of the Invention] According to the present invention, ■ a stilbene derivative with large hyperpolarizability is selected as a π-electron conjugated system; ■ a combination of donor and acceptor substituents is made into a dipole capable of asymmetric substitution; The central symmetry in the bulk state, for example, the crystalline state, is broken by the following three measures: 1) selection to increase the size of the moment; and 1) introducing an asymmetric substituent into the asymmetric site. It is possible to provide an organic second-order nonlinear optical material that exhibits a large second-order nonlinear optical effect by controlling the orientation to a bulk structure that can take advantage of second-order optical nonlinearity.

In addition, in the case of stilbene derivatives, the intermolecular cohesive force is greater than that of benzene derivatives due to strong π-electron interactions, and practical organic secondary nonlinear optics has excellent storage stability in the bulk state with lower sublimation and water absorption. material can be provided.

[Brief explanation of the drawing]

Figure 1 shows the powder particle size and 380 mm in the MMNS of the present invention.
Shows the strength relationship. Figure 2 shows acetone (A>) and benzene (
The results of powder method X-ray analysis of the crystal obtained from B) are shown.

Claims (9)

[Claims] (1) An organic secondary nonlinear optical material comprising a stilbene derivative represented by the following general formula [1] and having optical nonlinearity 10 times or more greater than that of urea. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [1] [However, D: Hammett's substituent constant σp, 0.2≧
Donor substituent selected from σp>-0.4 or halogen, A: Acceptor substituent selected from σp>0.2 with Hammett's substituent constant σp, R^1 to R^4: Hydrogen or It is an arbitrary substituent, and at least one represents an asymmetric substituent introduced into an asymmetric site. ] (2) Claim No. 1, characterized in that the donor substituent D is a hydroxyl group or an alkoxy group.
) The organic secondary nonlinear optical material described in item 2. (3) The organic secondary nonlinear optical material according to claim (1), wherein the acceptor substituent A is a nitro group. (4) The organic secondary nonlinear optical material according to claim (1), wherein three of R^1 to R^4 in formula [1] are hydrogen. (5) The organic secondary nonlinear optical material according to claim (1) or (4), characterized in that the asymmetric site into which the asymmetric substituent is introduced is the ortho position of the donor substituent D. . (6) The organic secondary nonlinear optical material according to claim (1), wherein the asymmetric substituent is a sterically hindered substituent. (7) The organic secondary nonlinear optical material according to claim (1), wherein the stilbene derivative is 4-methoxy-3-methyl-4'-nitrostilbene. (8) The organic secondary nonlinear optical material according to claim (1), wherein the stilbene derivative is 4-hydroxy-3-methoxy-4'-nitrostilbene. (9) Part or all of the hydrogen in the stilbene derivative is deuterated.
1) Organic second-order nonlinear optical material described in item 1).