JPH05107570A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain a large optical nonlinearity and to use the nonlinear material in a short wavelength region of visible light by constituting the nonlinear optical material of trans-stilbene derivs. expressed by specified formula to have no absorption a visible light region of >=415nm wavelength. CONSTITUTION:The nonlinear material consists of trans-stilbene derivs. expressed by formula I and has no absorption in a visible light region of >415nm wavelength. In the formula I, Rf is a perfluoroalkyl group, R1 is a hydroxy group or alkoxy group, each R2-R5 is one of hydrogen atoms, acetoamide groups, alkyl groups, alkoxy groups, and hydroxy groups. Namely, in this case, such a trans-stilbene deriv. is selected that has a perfluoroalkyl group such as trifluoromethyl group as an electron-withdrawing substituent showing relatively strong electron-withdrawing property and no absorption in the visible light region. Thus, large optical nonlinearity can be obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to organic nonlinear optical materials. More specifically, the present invention relates to an organic nonlinear optical material that can be used in a wide visible light region and is useful in fields such as wavelength conversion of laser light, optical communication, optical integrated circuits, and optical information processing.

[0002]

2. Description of the Related Art As a new element in the field of optoelectronics, many materials have been searched for in order to realize a nonlinear optical element.

Nonlinear optical materials are roughly classified into inorganic materials and organic materials, and conventionally, inorganic dielectrics such as KH ₂ PO ₄ and LiNbO ₃ are used. However, these inorganic non-linear optical materials have insufficient optical non-linearity, and a strong laser beam is required to exhibit a sufficient non-linear optical effect.

On the other hand, a series of organic compounds having a π-electron conjugated system has been attracting attention as a nonlinear optical material because of the magnitude of the optical nonlinearity of the molecule itself and the high-speed response. Poly
meric Materials, ACS Symposium Series 233 (198
3)).

The non-linear optical effect includes second-order, third-order, fourth-order,
········· There are n-th order effects, but of these, the ones expected to be applied are the second-order and third-order nonlinear optical effects. In order to develop a second-order nonlinear optical effect in a crystal of an organic compound, the crystal should not have a symmetry center.

As a method of removing the symmetry center of the crystal, introduction of a substituent into an asymmetric position of a molecule, use of a compound having chirality, use of an inclusion compound, selection of a counter ion in a molecular salt, intermolecular hydrogen Various methods have been proposed, such as the use of coupling and control of dipole moment.

For example, m in which a substituent is introduced at an asymmetric position
-Nitroaniline and 2-methyl-4-nitroaniline (hereinafter abbreviated as MNA) are known.
US Patent No.
4,199,698 and JP-A-55-500,960.

Many of these organic compounds have a nitro group as an electron-withdrawing substituent, and have light absorption resulting from this in the visible light region. Therefore, these organic compounds have absorption in the visible light region, particularly near 500 nm, although the optical nonlinearity is slightly excellent.

Further, since the stilbene derivative has a large π-electron conjugated system, it is known that the stilbene derivative exhibits a larger optical non-linearity per molecule as compared with a compound having a benzene ring as a π-electron conjugated system such as MNA. However, a compound having a large optical non-linearity in a crystal has been found.

While having a large optical nonlinearity, the stilbene derivative has absorption up to a considerably long wavelength side in the visible light region as compared with a compound having a benzene ring in a π-electron conjugated system.

As the organic non-linear optical material using the stilbene derivative, there are JP-A-1-207,724 and JP-A-1-173,017.

On the other hand, one of the application fields of organic nonlinear optical materials is a wavelength conversion element used for generating the second harmonic of a GaAlAs semiconductor laser.

By using the second harmonic of the GaAlAs-based semiconductor laser, the recording density of the optical disk using the conventional GaAlAs-based semiconductor laser can be quadrupled.

The characteristics required of the nonlinear optical material for the wavelength conversion element are large optical nonlinearity,
Moreover, it is a necessary condition that there is no absorption in the visible light region (415 nm or more) on the longer wavelength side than the wavelength region of the second harmonic.

[0015]

An object of the present invention is to provide an organic nonlinear optical material which exhibits a large optical nonlinearity and can be used even in a short wavelength region of visible light.

[0016]

In order to achieve the above object, the present invention has a perfluoroalkyl group having no light absorption in the visible light region as an electron-withdrawing substituent and has a large optical non-linearity. It is characterized by having a large π-conjugated transstilbene skeleton in order to have it.

That is, the following general formula

[0018]

[Chemical 2] (In the formula, R _f represents a perfluoroalkyl group, R ₁ represents a hydroxy group or an alkoxy group, and R ₂ , R ₃ , R ₄ and R ₅ represent a hydrogen atom, an acetamido group, an alkyl group, an alkoxy group or a hydroxy group. A transstilbene derivative represented by any of the above).

As mentioned above, p-nitroaniline, MN
Nitroaniline-based compounds such as A and m-nitroaniline show large optical nonlinearity at the molecular level due to the intramolecular charge transfer (CT) effect, while having light absorption in the visible region.

This is because the absorption due to the nitro group is in the vicinity of the visible light region, and further, the light absorption shifts to the longer wavelength side due to the bathochromic effect due to the charge transfer effect. That is, in order to obtain a compound that does not absorb in the visible light region, it is considered as one method to select a group other than the nitro group, which is a chromophore, as the electron-withdrawing substituent.

Further, by using a trans-stilbene skeleton having a large π-electron conjugated system instead of the benzene ring, the nonlinear optical characteristics can be enhanced, while the bathochromic effect of light absorption is further increased. That is, in order to balance the light absorption characteristics and the non-linear optical characteristics, it is necessary to select an appropriate electron-withdrawing substituent for the transstilbene skeleton.

In the case of the present invention, trans having a relatively strong electron-withdrawing property and a perfluoroalkyl group such as a trifluoromethyl group which does not have absorption in the visible light region as an electron-withdrawing substituent. This is achieved by selecting stilbene derivatives.

The above-mentioned perfluoroalkyl group represented by R _f is preferably a perfluoroalkyl group having 1 to 5 carbon atoms, such as trifluoromethyl group, pentafluoroethyl group, heptafluoro-n-propyl group, Heptafluoro-i-propyl group, nonafluoro-n-butyl group, nonafluoro-i-butyl group, nonafluoro-t
A butyl group and the like. More preferably, it is a trifluoromethyl group.

R ₁ is a hydroxy group or an alkoxy group, preferably an alkoxy group having 1 to 5 carbon atoms, and the alkoxy group includes a methoxy group, an ethoxy group, an n-propoxy group, an i-propoxy group, Examples thereof include n-butoxy group.

The substituents represented by R ₂ , R ₃ , R ₄ and R ₅ are hydrogen atom, acetamide group, alkyl group, alkoxy group or hydroxy group, preferably hydrogen atom, acetamide group and carbon atom. An alkyl group having 1 to 5 carbon atoms or an alkoxy group having 1 to 5 carbon atoms, and examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, and an n-butyl group. Are methoxy group, ethoxy group, n-propoxy group, i
—Propoxy group, n-butoxy group and the like.

Further, in order to largely break the symmetry of the crystal structure, at least one of R _{2 to} R ₅ is preferably a substituent other than a hydrogen atom.

Specific examples of the compound in the present invention are shown below. [Compound example]

[0028]

[Chemical 3]

[0029]

[Chemical 4]

[0030]

[Chemical 5]

[0031]

[Chemical 6] These trans-stilbene derivatives are obtained by synthesizing a corresponding substituted benzyl halide and a substituted benzaldehyde using a Wittig reaction to obtain a trans form by isomerization, and using a corresponding substituted phenylacetic acid and a substituted benzaldehyde as a catalyst. It can be obtained by a general method for synthesizing a stilbene derivative such as the above-mentioned synthetic method.

[0032]

The present invention will be described in more detail with reference to the following examples.

[0033]

Example 1 [Synthesis of 4-hydroxy-2′-trifluoromethyl transstilbene (Compound 1)]

[0034]

[Chemical 7] In a 100 ml three-necked flask equipped with a stirrer and a reflux condenser, α, α, α, trifluoro-2-toluylacetic acid 1
0.2 g (50 mmol), 4-hydroxybenzaldehyde 6.1 g (50 mmol), piperidine (30 m
1) was added, and the mixture was heated to reflux with stirring at an internal temperature of 120 ° C. for 15 hours.

After completion of the reaction, piperidine was distilled off to remove the residue by 20
Dissolve with 0 ml of chloroform, wash with 6% HCl, and concentrate the chloroform. After that, a yellow-brown solid was obtained by column chromatography using chloroform as a developing solvent (solid at room temperature, but before recrystallization, it was dissolved by heating at 40 to 60 ° C. to become a liquid).

2.06 g (yield 15.6%) of the crude product was recrystallized from hexane to give 1.
0 to 1.5 g was obtained. This was recrystallized with a polar solvent to obtain white needle crystals.

Identification was carried out by ¹ HNMR (FIG. 1) and IR (FIG. 2) in deuterated acetone, and 4-hydroxy-
It was confirmed to be 2'-trifluoromethyl transstilbene (Compound 1).

[0038]

[Test example]

[Evaluation of Second-Order Nonlinear Optical Properties and Light Absorption Properties at Molecular Level] In order to investigate the second-order nonlinear optical properties of the compound obtained in Example 1, the EFISH method of Levine et al. (BF Lenine et al. , J. App
l. Phys. , 50 , 2543 (1979)), and the second-order nonlinear hyperpolarizability β was measured.

The sample was dissolved in 1,4-dioxane to obtain N
Using the fundamental wave (wavelength 1064 nm) of the d: YAG laser, the second harmonic (532n) generated while applying an electric field
m) was observed, and the second-order nonlinear susceptibility β, which is a measure of the magnitude of the second-order nonlinearity at the molecular level, was determined using nitrobenzene as a reference sample.

Also, ethanol was used as a solvent to obtain 10 ⁻⁴ mo
A 1 / l solution was prepared and the absorption spectrum was measured with an ultraviolet / visible spectrophotometer to examine its visible light transmission characteristics. Where λ
_max is the maximum wavelength of light absorption on the longest wavelength side. λ _cut-off (cut-off wavelength) is a light absorption edge on the short wavelength side (wavelength with a transmittance of 95%). The measurement results are summarized in Table 1.

[Evaluation of Second-Order Nonlinear Optical Properties of Crystal] Ku
Powder method proposed by rtz et al. (SKKurtz, TTPerry, J.A.
ppl. Phys., 39, 3798 (1968)) and the presence of optical nonlinearity was investigated by observing the second harmonic.

The second harmonic (wavelength 532 nm) generated by irradiating the compound of Example 1 with an average particle size of 100 μm and irradiating it with the fundamental wave (wavelength 1064 nm) of an Nd: YAG laser.
Was observed. As a result, the second harmonic green light was confirmed.

[0043]

Comparative Example As a comparative example, the second-order nonlinearity of 2-methyl-4-nitroaniline, which is a typical organic nonlinear optical material, and 4-hydroxy-4′-nitrotransstilbene, which is a transstilbene derivative having a nitro group. The susceptibility β and the visible light transmittance were measured in the same manner as in Example 1. The results are shown in Table 1 together with Example 1.

As is clear from these results, the compound of the present invention is transparent to the visible light region in the short wavelength region and exhibits a large optical non-linearity as compared with the conventional compounds.

The compound of the present invention can be used not only in the form of crystals, but also in the form of being complexed with a polymer medium or being introduced into a polymer side chain.

[0046]

[Table 1]

[0047]

As described above, according to the compound of the present invention, the fact that the compound of the present invention is transparent to the short wavelength side of the visible light region as compared with the conventional materials is utilized, and it is used in the field of wavelength conversion and various information processing. In, it can be used in combination with a short wavelength light source. Further, it is particularly applicable to the generation of harmonics of short wavelength light sources such as GaAlAs semiconductor lasers.

[Brief description of drawings]

FIG. 1 is an example of a nonlinear optical material according to the present invention 4
FIG. 2 is a diagram showing a ¹ H NMR spectrum of —hydroxy-2′-trifluoromethyl transstilbene in deuterated acetone.

FIG. 2 is a view showing an IR spectrum of the same compound.

[Procedure amendment]

[Submission date] November 27, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

After completion of the reaction, piperidine was distilled off to remove the residue by 20
Dissolve with 0 ml of chloroform solution , wash with 6% HCl, and concentrate the chloroform solution . After that, a yellowish brown solid was obtained by column chromatography using a chloroform solution as a developing solvent (solid at normal temperature, but before recrystallization, it was dissolved by heating at 40 to 60 ° C. to become a liquid).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Suzuki 1618 Ida, Nakahara-ku, Kawasaki-shi In the Advanced Technology Research Laboratory, Nippon Steel Corporation (72) Inventor Tatsuo Nishiyama 3-6 Ibaraki, Akita City Co., Ltd. In Tochem Products (72) Inventor Tomomi Takezono 3-6 Ibaraki, Akita City In Tochem Products Co., Ltd.

Claims (1)

[Claims] 1. A general formula: (In the formula, R _f represents a perfluoroalkyl group, R ₁ represents a hydroxy group or an alkoxy group, and R ₂ , R ₃ , R ₄ and R ₅ represent a hydrogen atom, an acetamido group, an alkyl group, an alkoxy group or a hydroxy group. Which represents one of the above) and is 415 nm.
An organic nonlinear optical material having no absorption in the above visible light region.