JPH06294981A - Organic polymer nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain a nonlinear optical material having high SHG activity and excellent thermal stability by forming a styrene deriv. in which methoxy groups are introduced to 2- and 5-position and a cyano group and thienyl group are introduced to the beta-position. CONSTITUTION:This material is produced from a styrene deriv. in which methoxy groups are introduced to 2- and 5-position and a cyano group and a thienyl group in the beta-position. The org. nonlinear optical material has high melting point as 88 deg.C which is thermally stable, has the absorption edge in a short wavelength region, and shows high SHG activity. By using the org. material having excellent nonlinear properties, transmitting property, and temp. allowance for phase matching conditions, an org. nonlinear optical material having same characteristics as an expensive inorg. nonlinear optical material can be obtd. at low cost.

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 an optical control element or the like in a wide range of fields such as optical computers and optical communications. The present invention relates to an organic nonlinear optical material having high activity and good crystallinity.

[0002]

2. Description of the Related Art Non-linear optical materials are optical frequency conversion elements,
It has been put to practical use as an optical shutter, an EO converter, and the like. At present, inorganic ferroelectric crystals such as potassium dihydrogen phosphate (KDP) and lithium niobate are used as nonlinear optical materials. However, recently, attention has been paid to the magnitude of the nonlinear optical constant of an organic crystal, the speed of the nonlinear optical response, and the like, and vigorous development is being focused on organic second-order nonlinear optical materials.

As organic nonlinear optical materials for secondary effects, 2-methyl-4-nitroaniline (MNA), 3-methyl-4-nitropyridine-oxide (POM), etc. have been developed, and secondary materials of MNA have been developed. The nonlinear constant is 50 of KDP
It doubles.

It is widely known that an organic compound exhibiting such a strong nonlinear effect generally has an electron accepting group and an electron donating group with a π electron conjugated chain sandwiched therebetween. It is also known that the second-order nonlinear optical material must form a crystal without an inversion symmetry center.

[0005]

Since a single molecule of an organic nonlinear optical material is responsible for the origin of optical nonlinearity, a molecule having an asymmetric center has SHG (second harmonic generation) activity in principle. When the SHG active molecule is crystallized and used as an optical element, it is often encountered that the SHG activity as a whole is lost. Therefore, it is necessary to actually synthesize the molecular material, crystallize it, and evaluate the optical nonlinearity to determine whether the organic material can be used as the nonlinear optical element.

The optical non-linearity (supramolecular polarizability β) of an organic compound at the molecular level can be estimated from molecular orbital calculations, but in order to enhance the optical non-linearity of a single molecule, electron donation to a long conjugated system is required. It is only necessary to introduce a substituent having an acceptability and an acceptability. For example, a stilbene-based molecule having a large supramolecular polarizability β at the molecular level was one of the typical organic nonlinear optical materials. However, according to the ACS series literature, this type of material often has a symmetric center in the crystalline state and becomes SHG-inactive as a crystal in many cases.

Considering use as a wavelength conversion element, translucency in a molecular state or a crystalline state is an important factor. For example, stilbene-based materials often exhibit a peak of light absorption spectrum in the visible light region. Since the stilbene skeleton has a long conjugated system, if strong electron-accepting substituents (nitro group, etc.) and donating substituents (dimethylamino group, amino group, etc.) are introduced at the end of the conjugated molecule, light absorption in the visible light region will occur. Expected to show. Therefore, it is a subject to weaken the strength of the electron-accepting or donating substituent, to select the introduction position of the substituent in the stilbene skeleton, and to find a molecular material having no central symmetry as a crystal. The same can be said for the styrene-based material studied this time.

Further, the conventional inorganic nonlinear optical material has a melting point of about 1000 ° C. and is thermally stable even as an element.
However, there is a situation in which impurity diffusion occurs due to the high temperature growth and the optical damage intensity is low. On the other hand, the melting point of the organic material is generally about 100 ° C., the temperature coefficient of the refractive index that determines the phase matching condition is large, and the temperature tolerance of the wavelength conversion element tends to be low.

Therefore, it is an object of the present invention to provide an organic nonlinear optical material having high SHG activity and excellent thermal stability.

[0010]

The above object is achieved by an organic nonlinear optical material comprising a styrene derivative having a methoxy group at the 2,5 position and a cyano group and a thienyl group at the β position. You can

Styrene-based compounds are characterized by a π-electron conjugated system longer than benzene-based and pyridine-based nonlinear optical materials. Therefore, in consideration of the known trade-off relationship between the nonlinear constant and the translucency, a very large electron accepting property (nitro group) and electron donating property (dimethylamino group,
It is important to avoid introducing substituents (amino groups) simultaneously at the end of the conjugated system. (Β-Cyano) (β′-nitro) styrene represented by the following structural formula (II), in which a nitro group or a thienyl group as an electron-accepting substituent is introduced near the center of a styrene conjugated system, and (III) For each molecular species of (β-cyano) (β′-2-thienyl) styrene represented by, the optical non-linearity of one molecule and the maximum absorption wavelength were estimated by molecular orbital calculation (PPP method), and a thienyl group was introduced. Since the supramolecular polarizability β of the above-mentioned molecular species (III) was as large as 3 times, it was examined using a thienyl group as an electron-accepting substituent. As the electron-donating substituent,
A methoxy group was selected and the position of the substituent to be introduced was examined.
In addition, considering the size of the substituent, rotational freedom, and rigidity,
The reason for selecting the substituents was used.

This led to the discovery of the above-mentioned material that exhibits optical nonlinearity in the crystalline state. Further, since the styrene derivative has a high SHG activity, it is also useful as a material for second harmonic generation.

[0013]

[Chemical 1]

[0014]

[Chemical 2]

[0015]

The 2,5-dimethoxy- (β-cyano) (β′-2-thienyl) styrene represented by the following structural formula (I) has a maximum absorption wavelength λ _max of 382 nm (in 1,4-dioxane). is there. This does not have a large absorption in the wavelength region of blue light, and the SHG intensity by the powder method is twice the urea ratio, and it has sufficient non-linear optical characteristics for solving the problem.

[0016]

[Chemical 3]

[0017]

EXAMPLES The present invention will be described in more detail by way of examples.

According to the present invention, 2,5-dimethoxy- (β
-Cyano) (β'-2-thienyl) styrene was synthesized as follows.

2,5-dimethoxybenzaldehyde 2.
After dissolving 7 g (0.016 mol) in 150 ml of ethanol, 2.0 g of thiophene-2-acetonitrile
(0.016 mol) was added. 10 ml of ethanol solution in which 0.7 g of sodium ethylate was dissolved
Was dripped.

After stirring this solution at room temperature for 6 hours, the formed precipitate was filtered and washed with methanol to obtain the desired compound represented by the structural formula (I), 2,5-dimethoxy (β-cyano). ) (Β'-2-thienyl) styrene was obtained.

The yield was 68%. The maximum absorption wavelength is 382 nm (in 1,4-dioxane),
The melting point was 88 ° C. as measured by DSC.

This is based on MAP (reference: JL Ouda).
r and R. Hierle, J.M. Appl. Phy
s. , 48 (1977) 2699), which is higher than 69 ° C. Next, when the obtained fine powder crystal is irradiated with an Nd: YAG laser (wavelength = 1.064 μm), a second harmonic (SHG) is generated, and the wavelength of half the incident light (532 n) is generated.
m) green light was observed. It was confirmed that this SHG intensity was twice as high as that of urea, and that the SHG efficiency was stronger than that of urea.

Further, a plate crystal was easily obtained by a recrystallization operation from normal hexane, and a single crystal could be obtained by using this as a seed crystal.

[0024]

COMPARATIVE EXAMPLE The present inventors have a 2-methoxy- (β-cyano) represented by the following structural formula (IV) having a thienyl group and introducing a methoxy group at the 2-position or 4-position of the α-phenyl group. (Β′-2-thienyl) styrene, or 4-methoxy- (β-cyano) represented by the following structural formula (V)
(Β′-2-thienyl) styrene and (β-cyano) represented by the following structural formula (III) in which nothing is introduced.
Crystals were obtained by synthesizing each molecular species having (β'-2-thienyl) styrene.

[0025]

[Chemical 4]

[0026]

[Chemical 5]

[0027]

[Chemical 6]

However, as a result of evaluating these compounds by the powder method, SHG was inactive.

[0029]

According to the present invention, 2,5-dimethoxy-
The organic nonlinear optical material composed of (β-cyano) (β′-2-thienyl) styrene has a high melting point of 88 ° C. and is thermally stable. Furthermore, the absorption edge is on the short wavelength side and high SHG
Since it exhibits activity, it can be used in a wide range of fields as a nonlinear optical element.

Further, by using an organic material having excellent optical non-linearity, translucency, and temperature tolerance of phase matching conditions, it is possible to replace it with an expensive inorganic non-linear optical material and have characteristics equivalent thereto. An organic nonlinear optical material can be provided at a low price.

[Brief description of drawings]

FIG. 1 2,5-dimethoxy- (β-cyano) (β′-
2 is a graph showing the relationship between wavelength and absorbance of 2-thienyl) styrene in 1,4-dioxane.

Claims (2)

[Claims] 1. An organic nonlinear optical material comprising a styrene derivative having a methoxy group at the 2,5 position and a cyano group and a thienyl group at the β position. 2. A second harmonic generation material comprising a styrene derivative having a methoxy group at the 2,5 position and a cyano group and a thienyl group at the β position.