JPH0439056B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an organic second-order nonlinear optical material 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, there is a desire to discover materials that have large nonlinear optical effects and respond at high speed, and to realize higher performance nonlinear optical elements that have not been possible in the past. Therefore, many exploratory studies are being conducted with the aim of developing such high-performance materials. Conventionally, inorganic materials have been the main target of search, but no material satisfying the above requirements has been found. Therefore, in recent years, organic compounds having a π-electron conjugated system, which are expected to have a large nonlinear optical effect and a high-speed photoresponse in principle, 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 (ACS
symposium series 233 (1983): DJ Williams A
ngew.Chem.Int.Ed.Engl.23 p690 (1984) etc.). Representative materials developed to date include, for example, N-(4-nitrophenyl)-L-prolinol (NPP) [JP-A-59-21665], N-[5
Benzene and pyridine derivatives such as -(2-nitropyridyl)]-L-prolinol (PNP) and 2-acetylamino-4-nitro-N,N-dimethylaniline (DAN), 4'-dimethylamino-N- Stilbazoliums such as methyl-4-stilbazolium methosulfate (DMSM), and 4′-nitrobenzylidene-4-(N,
N-dimethyl)aniline, 4'-nitrobenzylidene-4-methylaniline (Procee dings
(Trudy) of the PNLevedeb Physics
Institute, Vol 98 (1982), Basov, NGEditor
(Consultants Bureau: New York, NY)
Shigorin, VD p77: “Materials and
Apparatus in QuantumRadio Physics”), 4′−
Examples include benzylidene aniline derivatives such as methylbenzylidene-4-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, donor and acceptor substituents are introduced into the π-electron conjugated system, as shown in the above representative material examples. Generally, the crystal structure of an organic compound is determined by the structure of each molecule and intermolecular cohesive forces such as hydrogen bonding during packing, Van-der Waals interaction, and dipole-dipole interaction. When a combination of strong donor and acceptor substituents, 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. becomes stronger. Such a compound tends to form a centrosymmetric crystal, which is a structure in which the dipoles of two molecules cancel each other out due to strong dipole-dipole interaction. However, such a centrosymmetric crystal does not exhibit second-order nonlinear optical effects. In conventional research, substituents, especially optically active substituents and hydrogen bond formation, are added to the asymmetric positions of the molecule in order to break the central symmetry of the crystal, which is a problem in producing second-order nonlinear optical effects in the crystalline state. Efforts have been made to introduce substituents with high potency, and there have been success stories with benzene and pyridine derivatives.
Representative examples include NPP, PNP and DAN. However, for example, the magnitude of the second-order nonlinear optical effect of NPP, which is reported to have achieved the optimum molecular orientation for producing the second-order nonlinear optical effect, is at most 150 times that of urea. Therefore, NPP
When trying to develop a material that has a second-order nonlinear optical effect even larger than that of benzene or pyridine derivatives, it is necessary to develop a material that has a second-order hyperpolarizability (second-order optical nonlinearity of molecules, It was necessary to achieve a non-centrosymmetric crystal structure and appropriate molecular orientation in a compound with a structure (first developed in the field). 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 small second-order nonlinear optical effects smaller than that of benzene derivatives were obtained. Therefore, in order to break the central symmetry of the crystal of a compound that has a long π-electron conjugated system as its parent skeleton and achieve appropriate molecular orientation, there are examples of studies that have considered the introduction of a salt structure with large steric hindrance. A typical example is DMSM, which has a large second-order hyperpolarizability and can control a non-centrosymmetric crystal structure using the steric hindrance of the counter anion to produce a large second-order nonlinear optical effect.
However, the salt structure of these compounds brings about properties that are unfavorable for nonlinear optical materials, such as hygroscopicity and crystalline polymorphism, so problems remain in terms of storage stability and processability. In stilbene derivatives whose parent skeleton is a long π-electron conjugated system that can increase the second-order hyperpolarizability by introducing donor and acceptor substituents,
It is expected that a material that exhibits a large second-order nonlinear optical effect in a crystalline state without the problems seen in DMSM can be obtained, but so far there has been no success story that surpasses NPP. [Problems to be Solved by the Invention] The object of the present invention is to solve the following problems in a stilbene derivative:
It solves the problem that it is difficult to form a non-centrosymmetric crystal structure due to its large dipole moment, and takes advantage of its large second-order hyperpolarizability.
An object of the present invention is to provide an organic nonlinear optical material that exhibits a second-order nonlinear optical effect and has excellent storage stability. That is, the present inventors have demonstrated through quantum chemical calculations that a stilbene derivative in which a donor substituent is introduced at the 4-position and an acceptor substituent is introduced at the 4'-position can have a large second-order hyperpolarizability. confirmed. 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: substituent constant σρ of the hook, 0.2
≧σρ>−0.4, or a donor substituent selected from halogen, A: Hammett's substituent constant σρ, and an acceptor substituent selected from σρ>0.2, R ¹ to ^{R 4} : 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 0.2≧σρ≧−0.4 or halogen at the 4-position, and an acceptor substituent selected from σρ>0.2, with Hammett's substituent constant σρ. at the 4'-position, and at least one asymmetric substituent having the effect of facilitating the formation of non-centrosymmetric crystals is present at the asymmetric site of the phenyl group substituted with the donor group. In other words, the feature of the present invention is that a stilbene derivative with large hyperpolarizability is
The selection of electronic conjugated systems. The combination of donor and acceptor substituents was selected to provide a dipole moment size that allows for control of molecular orientation. In addition, an asymmetric substituent was introduced into an asymmetric site. Through these three techniques, the central symmetry in the bulk state, for example, the crystalline state, is broken, and the orientation is controlled to create a bulk structure that takes advantage of the second-order optical nonlinearity of the molecule, making it possible to produce large second-order nonlinear optical effects. It is in the point that I made it. As shown in Comparative Examples 1 and 2, it is difficult to stably form a crystal that exhibits a large second-order nonlinear optical effect only by making improvements. By applying further innovations, they succeeded in making it easier to form crystals that exhibit large second-order nonlinear optical effects. 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 compares the solubility of the materials of the present invention in water with the known examples of NPP, PNP, and DAN. 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, the conventionally used material. 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, hydroxymethyl,
hydroxyalkyl groups such as hydroxyethyl,
Examples include chain or branched alkyl groups such as methyl, ethyl, and t-butyl, alkylsilyl groups such as trimethylsilyl, mercaptoalkyl groups such as mercaptomethyl, alkanoylamino groups such as acetylamino, mercapto groups, and halogens. Acceptor substituents include nitro groups, alkylsulfonyl groups such as methylsulfonyl, cyano groups, sulfamoyl groups, alkylsulfamoyl groups such as methylsulfamoyl, trifluoromethyl groups, formyl,
Acyl groups such as acetyl, trifluoromercaptomethyl groups, alkylsulfinyl groups such as methylsulfinyl, carboxy groups, alkoxycarbonyl groups such as methoxycarbonyl and ethoxycarbonyl, carbamoyl groups, alkylcarbamoyl groups such as methylcarbamoyl, triflio Examples include lomethoxy group and halogen. Since halogen has both donor and acceptor properties, 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 during molecular packing. It is the basis. In other words, it is a group that can break the central symmetry of both the molecule itself and the entire crystal and control 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 packing, 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, a methoxy group, an ethoxy group, a methyl group is used as a sterically hindered substituent of an appropriate size, and an ethyleneoxy group is used as an example in which an asymmetric substituent and a donor group are connected. ing. Furthermore, for the same reason, it is desirable that the number of asymmetric substituents be small. Therefore, preferably R ¹ to R ⁴
Three of them 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 stilbene compounds, in which aldehyde and phenylacetic acid derivatives are subjected to heating, dehydration, decarboxylation, and condensation 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, in the nonlinear optical compound, 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, 4-methoxy-
3-Methyl-4'-nitrostilbene (MMNS)
As shown in the examples, it is possible to produce bulk single crystals by a solution method, and in addition, it is possible to produce bulk single crystals by a solution method, or by vapor phase growth such as melting and slow cooling on a substrate, vapor deposition on a substrate, or sublimation. It is also possible to produce thin film single crystals. Bulk single crystals, thin film single crystals, etc. produced in this manner are useful for constructing nonlinear optical elements such as wavelength conversion elements, parametric oscillators, and optical switches, as well as optical information processing and optical communication systems using them. [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] In a 100 ml three-necked flask equipped with a reflux condenser and magnetic stirrer, add 4.56 g (30 mmol) of 3-methoxy-4-hydroxybenzaldehyde (vanillin) and 5.43 g.
(30 mmol) of p-nitrophenyl acetic acid was added,
About 18 ml of piperidine was added, and the mixture was heated to reflux at an oil temperature of about 120° C. while stirring for about 8 hours. The reaction solution turned red-black. After confirming the completion of the reaction using thin layer chromatography using chloroform as a developing solvent, stirring was stopped. When piperidine is removed using a rotary evaporator, a tar-like substance remains. If 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 recrystallized with acetonitrile, orange angular crystals were obtained, which were collected by filtration and dried under vacuum. [Target product 4.98g (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 (-OCH ₃ ); 1636, 970 (-
CH=CH-); 1506-1518, 1328 ( _-NO2 );
1250, 1030 (−OCH ₃ ) 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 (SKKurtz, TTPerry, J.Appl.Phys.
39 3798 (1966)). The light source used for the measurement was a Nd:YAG laser (oscillation wavelength
1.064 μm), and the sample was ground to about 100 μm in a mortar. Laser irradiation conditions are pulse width 200nsec, repetition rate 10Hz, peak power density approx.
It was conducted at 30MW/ ^cm2 . The measurement results are shown in Table 1. HMNS according to the invention
showed 70 times higher SHG than the standard known compound urea. Furthermore, when the solubility in water was investigated, the HMNS according to the present invention was found to be substantially insoluble (Table 3
reference. ) Example 2 3-Ethoxy-4-hydroxy-4'-nitrostilbene (HENS). [Synthesis] The reaction and separation and purification were carried out in exactly the same manner as in Example 1, except that 4.98 g (30 mmol) of 3-ethoxy-4-hydroxybenzaldehyde and 5.43 g (30 mmol) of p-nitrophenyl acetic acid were used. When the orange crude crystals were recrystallized with acetonitrile, yellow-orange needle-shaped crystals (approximately 7 x 5 x 3 mm) were obtained, which were collected by filtration and vacuum-dried. [Objective 5.90g (yield 68.9%) Melting point 161-163°C] Identification was performed by IR and elemental analysis (see Table 2). (IR; KBr tablet method cm ^-1 ) 3430 (-OH); 1632, 970 (-CH=CH-); 1502
~1506, 1325 (−NO ₂ ); 1438 (−OCH ₂ CH ₃ ); 1250, 1030 (−
OC ₂ H ₅ ) Next, the SHG measurement results of this compound are shown in Table 1. HENS according to the present invention exhibited 30 times more SHG than the standard known compound urea. Furthermore, when the solubility in water was examined, HENS according to the present invention was found to be substantially insoluble (Table 3
reference). Example 3 4-Methoxy-3-methyl-4'-nitrostilbene (MMNS). [Synthesis] The reaction was carried out in exactly the same manner as in Example 1, except that 6.03 g (30 mmol) of 3-methyl-p-anisaldehyde, 5.97 g (33 mmol) of p-nitrophenyl acetic acid, and about 5 ml of piperidine were used. 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 bulk crystals were obtained, which were collected by filtration and dried under vacuum. [Target object 7.12g (yield 80.2%) Melting point 111-111.5°C] Identification was performed by IR and elemental analysis (see Table 2). (IR; KBr tablet method cm ^-1 ) 2960, 2865 (-OH ₃ ); 2850 (-OCH ₃ ); 1635,
967 (-CH=CH-); 1503, 1320 ( _-NO2 );
1450, 1470 (−OCH ₃ , −CH ₃ ); 1240, 1024 (−
OCH ₃ ) When 5g of MMNS is dissolved in 50ml of acetonitrile while hot, left to cool, and crystallized by solvent evaporation at room temperature, yellow lumpy crystals of about 1 x 1 x 1 cm are obtained in about 1 month. Ta. Polarized light microscopy revealed that this crystal was a single crystal. Next, Table 1 shows the measurement results of SHG of this compound. MMNS according to the present invention exhibited an extremely large SHG of 650 times that of urea, which is a standard known compound, or about 4 times that of NPP, which shows 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. Furthermore, when the solubility in water was examined, the MMNS according to the present invention was found to be substantially insoluble (Table 3
reference). Example 4 5-(p-nitrostyryl)-2,3-dihydrobenzofuran (EONS) [Synthesis 1] In a 500 ml three-neck flask equipped with a reflux condenser and a magnetic stirrer, 25 g of formylating agent ((chloromethylene)dimethylammonium chloride) and 200 ml of chloroform were added and stirred to disperse. 23g of 2,3-dihydrobenzofuran was added and reacted overnight at room temperature. Furthermore, the reaction was completed by heating under reflux for 5 hours. The reaction solution cooled to room temperature was poured into 500 ml of 0.2N aqueous sodium hydroxide solution, and after vigorous stirring, the chloroform soluble content was extracted. The extract was washed with water and dried, and chloroform was distilled off under reduced pressure to obtain 21 g of the desired aldehyde. [Synthesis 2] In a 100 ml three-neck flask equipped with a reflux condenser and a magnetic stirrer, put 6 g of 5-formyl-2,3-dihydrobenzofuran obtained in [Synthesis 1] above and 7.3 g of p-nitrophenyl acetic acid, and add about 2 ml. of piperidine was added thereto, and the mixture was heated to reflux while stirring at an oil temperature of about 120°C for about 1.5 hours. After cooling to room temperature, the solidified reaction product was recrystallized from methanol to obtain 1.8 g of a brown-yellow solid. This was dissolved under heat in cyclohexane/acetone (volume ratio 2:1), treated with activated carbon, and then recrystallized to obtain 0.7 g (yield 5.3%) of yellow needles. Melting point is 196.5℃
It was hot. Identification was performed by IR and elemental analysis (see Table 2). (IR; KBr tablet method cm ^-1 ) 2900 to 3060 (-OH ₂ -CH ₂ -O-); 1630 (-CH
=CH-); 1340 ( _-NO2 ); 1250 (C-O-C) For various measurements, crystallization from ethyl acetate and vacuum drying was used. Next, Table 1 shows the measurement results of SHG of this compound. EONS according to the invention exhibited 25 times more SHG than the standard known compound urea. Furthermore, when the solubility in water was examined, the EONS according to the present invention was found to be substantially insoluble (Table 3
reference). Comparative Example 1 4-Hydroxy-4'-nitrostilbene (HNS). [Synthesis] The reaction and separation and purification were carried out in exactly the same manner as in Example 1, except that 3.66 g (30 mmol) of p-hydroxybenzaldehyde and 5.43 g (30 mmol) of p-nitrophenyl acetic acid were used. When the orange crude crystals were recrystallized with chloroform, yellow-orange angular crystals were obtained, which were collected by filtration.
Vacuum dried. [Target product 4.33g (yield 65.3%) Melting point 209-210°C] Identification was performed by IR and elemental analysis (see Table 2). (IR; KBr tablet method cm ^-1 ) 3440 (-OH); 1630, 956 (-CH=CH-); 1502,
1328( _-NO2 ) Next, Table 1 shows the measurement results of SHG of this compound. 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] 4.08g (30mmol) of p-anisaldehyde and
The reaction and separation and purification were carried out in exactly the same manner as in Example 3, except that 5.43 g (30 mmol) of p-nitrophenyl acetic acid was used. When the yellow crude crystals were recrystallized with acetone, yellow-orange plate crystals were obtained. This was collected by filtration and vacuum dried. [Target product 6.35g (yield 83.0%) Melting point 134-135°C] When MNS was recrystallized with benzene, yellow plate-like crystals were obtained. Identification was performed by IR and elemental analysis (see Table 2). (IR; KBr tablet method cm ^-1 ) 2830 (-OCH ₃ ); 1628, 960 (-CH=CH-);
1500-1510, 1325( _-NO2 ) Next, Table 1 shows the measurement results of SHG of this compound. MNS recrystallized with acetone showed only the same level of SHG as urea, a standard known material. On the other hand, MNS recrystallized with benzene showed 67 times more SHG than urea. Figure 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 stable production of 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】

【table】

【table】

[Table] [Effects of the Invention] According to the present invention, a stilbene derivative having a large hyperpolarizability is
The combination of donor and acceptor substituents was selected to have a dipole moment size that allowed asymmetric substitution, and in addition, the asymmetric substituent was introduced into the asymmetric site. thing,
Through these three techniques, the central symmetry of the bulk state, for example, the crystalline state, can be broken, and the orientation can be controlled to create a bulk structure that takes advantage of the second-order optical nonlinearity of the molecules. A second order nonlinear optical material can be provided. 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 drawings]

Figure 1 shows the powder particle size and MMNS of the present invention.
The relationship between SHG intensity is shown. Figure 2 shows a comparative example MNS
The results of powder method X-ray analysis of crystals obtained from acetone A and benzene B are shown below.

Claims (1)

[Scope of 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. [However, D: substituent constant σρ of the hook, 0.2
≧σρ>−0.4, or a donor substituent selected from halogen, A: Hammett's substituent constant σρ, and an acceptor substituent selected from σρ>0.2, R ¹ to ^{R 4} : hydrogen or any substituent and at least one represents an asymmetric substituent introduced at an asymmetric site. 2. The organic secondary nonlinear optical material according to claim 1, wherein the donor substituent D is a hydroxyl group or an alkoxy group. 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, wherein 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 stilbene derivative is 4-hydroxy-3-
The organic secondary nonlinear optical material according to claim 1, which is methoxy-4'-nitrostilbene. 9. The organic secondary nonlinear optical material according to claim 1, wherein some or all of the hydrogens in the stilbene derivative are deuterated.