JP2980801B2 - Organic nonlinear optical material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear optical material used as a light control element in a wide field such as an optical computer and an optical communication, and more particularly, it is stable at room temperature, has excellent light damage strength, and The present invention relates to an organic nonlinear optical material comprising a styrene derivative having high SHG (second harmonic generation) activity and good crystallinity.

[0002]

2. Description of the Related Art Non-linear optical materials are used as light control elements in a wide range of fields such as optical computers and optical communications. For example, wavelength conversion elements, optical shutters, or EOs are used.
It is practically used as a (photoelectric) converter. As such a nonlinear optical material, a ferroelectric crystal made of an inorganic compound such as potassium dihydrogen phosphate (KDP) or lithium niobate is currently used.

However, recently, attention has been paid to the magnitude of the nonlinear optical constant and the speed of the nonlinear optical response of the organic crystal, and the development of organic nonlinear optical materials has been vigorously focused on the second-order nonlinear effect. It is being advanced. Organic nonlinear optical materials for such second-order nonlinear effects include 2-
Methyl-4-nitroaniline (MNA), 3-methyl-
4-Nitropyridine-oxide (POM) and the like have been developed. The second-order nonlinear constant of MNA reaches 50 times that of KDP, indicating a strong nonlinear effect.

It is widely known that an organic compound exhibiting such a strong nonlinear effect generally has an electron-withdrawing group and an electron-donating group with a π-electron conjugated chain interposed therebetween. The organic nonlinear optical material for the second-order nonlinear effect is
It is also known that it is necessary to construct a crystal without a center of inversion symmetry.

Japanese Patent Application Laid-Open No. 3-140927 discloses an organic nonlinear optical material for such a second-order nonlinear effect.
A styrene derivative having a hydroxy group and a methoxy group as electron donating groups and two cyano groups as electron accepting groups is disclosed, but the maximum absorption wavelength of this compound is 453n.
m, the cutoff wavelength was 501 nm, and the nonlinear optical effect was insufficient.

[0006]

In the organic nonlinear optical material, since one molecule is responsible for the origin of optical nonlinearity, all molecules having an asymmetric center have SHG activity in principle. However, when a molecule having SHG activity is crystallized and used as a nonlinear optical material, the SHG in the entire crystal is used.
Loss of activity is often encountered. Therefore, to determine whether an organic compound can be used as a nonlinear optical material, it is necessary to actually synthesize and crystallize a molecule and evaluate the optical nonlinearity.

The optical nonlinearity (supramolecular polarizability β) at the molecular level of an organic compound can be estimated from molecular orbital calculations. In order to increase the optical nonlinearity of one molecule, an electron-donating substituent and an electron-accepting substituent may be introduced into a long π-electron conjugated system. For example, having a long conjugate system,
A stilbene compound having a large supramolecular polarizability β at the molecular level was one of the typical organic nonlinear optical materials. However, since such compounds have a center of symmetry in a crystalline state, they often become SHG inactive in a crystalline state.

When considering the case where a nonlinear optical material is used as a wavelength conversion element, light transmission in a molecular state or a crystalline state is an important factor. For example, many stilbene-based compounds show a light absorption spectrum peak in a visible light region, and such compounds are not suitable as a wavelength conversion element. Since the π-electron conjugated system of the stilbene skeleton is long, when a substituent with a strong electron-accepting property (such as a nitro group) and a substituent with a strong electron-donating property (such as a dimethylamino group or an amino group) are introduced at the end of the conjugated system, It is expected to show light absorption in the light region. Therefore, the electron-accepting or electron-donating substituent of the electron-accepting substituent is weakened, and the position of introduction of the substituent in the stilbene skeleton is selected so that the center of symmetry does not exist in a crystalline state. It is necessary. The same is conceivable for styrene compounds.

Further, the melting point of the conventional inorganic nonlinear optical material is about 1000 ° C., and it is thermally stable even when used as an optical element. However, the inorganic nonlinear optical material has a problem that impurity diffusion occurs due to high-temperature growth, and the optical damage strength is reduced. On the other hand, the melting point of the organic nonlinear optical material is generally about 100 ° C., and the temperature-dependent coefficient of the refractive index that determines the phase matching condition is large. For this reason, when used as a wavelength conversion element, there was a tendency that the use temperature tolerance was low and the composition was thermally unstable.

The present invention has been made to solve the above-mentioned problems of the prior art, and has a conversion wavelength of 400 nm.
It does not have large absorption in the longer wavelength region, is thermally stable,
An object of the present invention is to provide an organic nonlinear optical material having excellent light damage strength, high translucency and high SHG activity in a crystalline state.

[0011]

In the organic nonlinear optical material of the present invention, three methoxy groups are introduced into the α-phenyl group, a thienyl group is introduced into the β′-position, and a cyano group is introduced into the β-position. It consists of a styrene derivative, whereby the above object is achieved.

In a preferred embodiment, the methoxy group is introduced at the 2-, 4- and 5-positions of the phenyl group.

In a preferred embodiment, the thienyl group is a 2-thienyl group.

Hereinafter, the present invention will be described in detail.

In the organic nonlinear optical material of the present invention,
A thienyl group and a cyano group are introduced as electron-accepting substituents at the β-position of the styrene derivative.

Styrene compounds have a longer π-electron conjugate system than benzene compounds and pyridine compounds. Therefore, in consideration of translucency, it is preferable to simultaneously introduce a strong electron-accepting substituent (such as a nitro group) and a strong electron-donating substituent (such as a dimethylamino group or an amino group) into the end of the conjugated system. Absent. Therefore, in the organic nonlinear optical material of the present invention, the vicinity of the central part of the styrene conjugate system (β
), An electron-accepting substituent was introduced. In addition, the molecular orbital calculation (PP
When the optical nonlinearity and the maximum absorption wavelength of one molecule were estimated by the P method, the thienyl group-introduced molecule (b) had a supramolecular polarizability β of three times as large. Was selected as a thienyl group. In the organic nonlinear optical material of the present invention, the 2-thienyl group is more stable than the 3-thienyl group and is preferred.

[0017]

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In order to obtain a nonlinear optical material, the nonlinearity is usually increased by introducing an electron-accepting substituent and an electron-donating substituent respectively at both ends of a conjugated system.
In the present invention, a novel optical material having excellent optical nonlinearity was obtained by introducing a cyano group, which is a substituent having a weak electron accepting property, at a position in the middle of a conjugated system.

Further, in the organic nonlinear optical material of the present invention, a methoxy group is introduced as an electron-donating substituent into the α-phenyl group in the styrene derivative.

The methoxy group, which is an electron donating substituent, has no center of symmetry in consideration of the positions of the thienyl group and the cyano group, which are electron accepting substituents, and further has an electron donating property. Selected for not being too strong.

Considering the size, rotational freedom and rigidity of the methoxy group, the introduction of the methoxy group at the 2-, 4- and 5-positions of the phenyl group provides good rotational freedom and rigidity. It turned out to be.

As a result, an organic nonlinear optical material exhibiting optical nonlinearity in a crystalline state was obtained.

The organic nonlinear optical material of the present invention is, for example,
It can be synthesized by a condensation reaction between 2,4,5-trimethoxy-benzaldehyde and thiophen-2-acetonitrile. This condensation reaction can be performed in an organic solvent such as ethanol in the presence of a catalyst such as sodium ethylate.

By dissolving the powdery crystal obtained by the above reaction in an organic solvent such as cyclohexane and recrystallizing the same, a plate-like crystal can be obtained, and a single crystal can be obtained by using this as a seed crystal. it can.

[0025]

The organic nonlinear optical material according to the present invention comprises a styrene derivative having a long π-electron conjugate system, in which a cyano group and a thienyl group are introduced as electron-accepting substituents, and a methoxy group is introduced as electron-donating substituents. ing. Therefore, the supramolecular polarization β at the molecular level is large, and the optical nonlinearity of one molecule can be increased.

Since the thienyl group and the cyano group as the electron-accepting substituents are introduced near the center (β-position) of the styrene conjugated system, light absorption in the visible light region causes a decrease in translucency. Absent.

The methoxy group has no center of symmetry, and the methoxy group is introduced at the 2-, 4- and 5-positions. Therefore, a high SHG activity can be exhibited in a crystalline state.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

(Example) After dissolving 2.4 g (0.012 mol) of 2,4,5-trimethoxybenzaldehyde in 150 ml of ethanol, 1.5 g (0.012 mol) of thiophen-2-acetonitrile was added. 10 ml of an ethanol solution in which 0.7 g of sodium ethylate was previously dissolved was added dropwise thereto.

After the solution was stirred at room temperature for 6 hours, the resulting precipitate was filtered and washed with methanol. As described above, fine powder crystals of 2,4,5-trimethoxy- (β-cyano) (β′-2-thienyl) styrene represented by the following formula (c) were obtained in a yield of 46%.

[0031]

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The absorption characteristics of this styrene derivative in 1,4-dioxane were measured. As shown in FIG. 1, the maximum absorption wavelength was 392 nm and the cutoff wavelength was 442 nm, which was on the short wavelength side. No significant absorption was seen in the region. The melting point was 139 ° C. as measured by DSC, and MAP (methyl- (2,4-dinitrophenyl) aminopropanoate) (J.L.
and R. Hierle, J .; Appl. Phys
s. , 48 (1977) 2699), which is higher than the melting point of 69 ° C., thereby improving the use temperature tolerance. The obtained styrene derivative was stable at room temperature, had good crystallinity, and was excellent in light damage strength.

When the obtained fine powder crystal is irradiated with a Nd: YAG laser (wavelength = 1.64 μm), a second harmonic (SHG) is generated and a half wavelength (532n) of the incident light is generated.
m) green light was observed. The SHG intensity was equal to the urea ratio, and it was confirmed that the SHG activity was very high, equivalent to that of urea.

From the above results, this styrene derivative is
It can be seen that the organic nonlinear optical material has excellent characteristics.

Further, by dissolving the obtained fine powder crystal in cyclohexane and performing a recrystallization operation, a plate-like crystal was easily obtained, and a single crystal could be obtained by using this as a seed crystal.

Comparative Example 1 A compound having a methoxy group introduced at the 2-position of the phenyl group at the α-position (the following formula (d)) was synthesized to obtain fine powder crystals. When these compounds were evaluated by the same powder method as in the example, they were SHG-inactive.

(Comparative Example 2) A compound in which a methoxy group was introduced into the 4-position of the α-phenyl group (the following formula (e)) was synthesized to obtain fine powder crystals. When these compounds were evaluated by the same powder method as in the example, they were SHG-inactive.

Comparative Example 3 A compound in which nothing was introduced into the α-phenyl group (the following formula (b)) was synthesized to obtain fine powder crystals. When these compounds were evaluated by the same powder method as in the example, they were SHG-inactive.

[0039]

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[0040]

As is evident from the above description, the organic nonlinear optical material of the present invention has a high melting point, so that it can be used at an excellent temperature and is thermally stable. Further, since no large absorption in the visible light region is observed and high SHG activity is exhibited in a crystalline state, it can be used as a nonlinear optical element in a wide range of fields. The organic nonlinear optical material of the present invention is, for example, a blue SH for digital video discs.
It can be used as a G element material.

As described above, the organic nonlinear optical material of the present invention, which is excellent in optical nonlinearity, translucency, temperature tolerance of phase matching conditions, and optical damage strength, can provide the characteristics of an expensive inorganic nonlinear optical material at a low price. Can be provided.

For example, 2,4,5-trimethoxy- (β
-Cyano) (β'-2-thienyl) styrene has a maximum absorption wavelength λmax of 392 nm (in 1,4-dioxane) and does not have a large absorption in a blue light wavelength region. It has a melting point of 139 ° C. and is thermally stable. S by powder method
The HG intensity is equal to the urea ratio and has a high SHG intensity.

[Brief description of the drawings]

FIG. 1. 2,4,5-Trimethoxy- (β-cyano)
It is a figure which shows the relationship between the wavelength in (4 -'- thienyl) styrene in 1, 4- dioxane, and an absorbance. The vertical axis indicates absorbance and the horizontal axis indicates wavelength.

Claims (3)

(57) [Claims] 1. An organic nonlinear optical material comprising a styrene derivative in which three methoxy groups are introduced into an α-phenyl group, a thienyl group is introduced into a β′-position, and a cyano group is introduced into a β-position. 2. The methoxy group is the same as the phenyl group.
The organic nonlinear optical material according to claim 1, which is introduced at the 4-, 4-, and 5-positions. 3. The organic nonlinear optical material according to claim 1, wherein the thienyl group is a 2-thienyl group.