JPH02252728A - Nonlinear organic optical material - Google Patents

Abstract

PURPOSE:To obtain the title material which is soluble in a solvent, can be formed into a noncentrosymmetric thin film by a simple thin film formation method and has a high-performance quadratic nonlinear optical effect by using a specified pi-conjugated high-molecular polymer. CONSTITUTION:A nonlinear organic optical material is obtained by using pi-conjugated high-molecular copolymers of formula I (wherein R<1> is a 1-20C alkyl or alkoxy; X<1> is -S- or -NH; and l is an integer) and/or formula II (wherein R<2> is H, a 1-20C alkyl or alkoxy; R<3> is a 1-20C alkyl or alkoxy; X<2> and X<3> are each -S- or -NH-, and m and n are integers). Although conventional pi-conjugated polymers are chiefly insoluble and infusible and therefore are lacking in controllability of process, the above material comprises a solvent-soluble pi-conjugated polymer and is one which can show a high-performance quadratic nonlinear optical effect and can be formed into a noncentrosymmetric thin film by a simple film formation method.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to novel organic nonlinear optical materials.

[Prior art/issues to be solved by the invention] Nonlinear optical materials can generate second harmonics (hereinafter referred to as SHG),
It is an optical abrasive used in wavelength conversion such as third harmonic generation (hereinafter referred to as THG), and active optical devices such as optical switches and phase conjugate wave generation, and will be a core material in the future optical information processing field. It is expected to be a material that plays a role. Among them, approximately 700r+a due to band gap limitations.
There is a strong desire for an SHG element that can efficiently halve the oscillation wavelength of a semiconductor laser, which is difficult to oscillate at a short wavelength of + or less. This demand is particularly noticeable in the field of optical disk devices, where by halving the oscillation wavelength, the condensing area can be reduced to 1/4, and as a result, the recording density can be quadrupled.

The most widely used nonlinear optical material has been inorganic ferroelectric crystals such as KDP. but,
These inorganic materials have the disadvantage of having small nonlinear optical constants. In particular, since the efficiency for second harmonic generation is proportional to the square of the incident optical power, inorganic nonlinear optical materials are often used in industrial fields that require the use of relatively low-power light sources such as semiconductor laser light. The reality is that it cannot be used.

Against this background, organic materials are attracting attention as materials that can generate second harmonics with high efficiency (D.
AC3 Symposium Series (AC3Symp, Ser.), Vol.

233, Nonlinear Optical Pro
partiesofOrganic and Poly
+ger1c Materals) J (1983)
). However, among these organic materials, low-molecular organic nonlinear optical materials have problems in terms of stability and properties. In order to obtain large nonlinear optical constants, it is thought that polymeric materials with long π-conjugation lengths are desirable;
Many polymer compounds with long conjugation lengths are insoluble and infusible, and have the disadvantage of being extremely difficult to process.

On the other hand, in organic nonlinear optical materials, there are two main factors that govern their nonlinear optical constants: first, one molecule in the case of a low-molecular compound, and the repeating unit in the case of a polymer material. is the molecular hyperpolarizability of the monomer units, and the second is their arrangement. When a thin film is used as a second-order nonlinear optical material for generating second-order harmonics, it is desirable that each molecule is arranged so that all molecular hyperpolarizabilities are strengthened. Therefore, it is necessary to align the molecules in the normal direction or in one direction within the plane. (In any case, these highly oriented materials can be used in various ways, such as transmission type or waveguide type.

) However, thin films produced using conventional and simple thin film formation methods, such as spin coding, casting, dipping, barcoding, and roll coating, are in an amorphous state with no order. It could not be used as a second-order nonlinear optical material, such as for second-order harmonic generation, which requires a structure without central symmetry.

In addition, as a method for obtaining such highly oriented organic thin films,
Although the Langmuir-Prodgett method (LB method) and the organic molecular beam epitaxy method (OMBE method) have already been proposed, these methods are currently very complicated and complicated.

As described above, conventionally, there has been no method of forming a polymer compound with a long π-conjugation length into a thin film without central symmetry using a simple thin film forming method.

[Means for Solving the Problems] The present invention solves the above conventional problems, has large nonlinear optical properties, is easy to form into a film, and has central symmetry. second-order nonlinear optical effects such as SHG, optical mixing, parametric oscillation, and electro-optic effects;
In particular, this work was made to provide an organic nonlinear optical material exhibiting a novel second-order nonlinear optical effect consisting of a polymer compound with a long π conjugation length (hereinafter referred to as a π-conjugated polymer) that has SHG activity. It is.

In other words, in the past, many π-conjugated polymers were insoluble and infusible, so they lacked process controllability, but the material of the present invention consists of π-conjugated polymers that are soluble in solvents, and can be easily formed into thin films. It is a material that exhibits a high-performance second-order nonlinear optical effect that allows the creation of thin films without central symmetry depending on the manufacturing method.

The present invention provides a π-conjugated system represented by the general formula (1): (wherein R1 is an alkyl group or an alkoxyl group having 1 to 2 carbon atoms, Xi is -8- or -Nll-1g is an integer) High molecular polymer and/or general formula (■): (wherein, R2 is a hydrogen atom or an alkyl group or alkoxyl group having 1 to 2 carbon atoms, R3 is an alkyl group or alkoxyl group having 1 to 20 carbon atoms, ' and x3 are -
The present invention relates to an organic nonlinear optical material having a second-order nonlinear optical effect, which is made of a π-conjugated polymer copolymer represented by S- or -NH-1m and n are integers.

[Function] The material of the present invention is composed of a solvent-soluble π-conjugated polymer, and a simple thin film manufacturing method can be used, so the device manufacturing process is significantly facilitated, and it can also be used for highly efficient second-order nonlinear optics. It is a nonlinear optical material that exhibits effects.

[Example] The organic nonlinear optical material of the present invention comprises: - a π-conjugated polymer represented by the formula (I): and/or - a π-conjugated polymer represented by the formula (I): Consists of merging.

- R1 in formula (1) is an alkyl group or alkoxyl group having 1 to 2 carbon atoms. By introducing the alkyl group or alkoxyl group as a side chain, the π-conjugated polymer becomes soluble, and the larger the number of carbon atoms, the easier it is to dissolve in a solvent. However, it is the thiophene ring and pyrrole ring that contribute to the nonlinear optical properties, and the alkyl and alkoxyl groups do not contribute to the nonlinear optical properties, so the larger the number of carbon atoms in the side chain, the higher the π-conjugated system. The nonlinear optical properties of the entire molecule are degraded. Therefore, from the viewpoint of these balances, the number of carbon atoms in the alkyl group or alkoxyl group is preferably 1 to 12. xl represents -S- or -NH-. g represents an integer, 5 to 50,000,
Furthermore, 20 to 50,000 is preferable. Those with a high degree of polymerization have good nonlinear optical properties, and if p is less than 5, it will be difficult to solidify during molding. Furthermore, in order to obtain a π-conjugated polymer with high coating properties, it is preferable that the molecular weight is sufficiently large.

In addition, - RI in the polymer represented by formula (I)
Each of Xi does not need to be of one type.

R2 in general formula (II) is a hydrogen atom or has 1 to 1 carbon atoms.
20 alkyl or alkoxyl groups.

When R2 is an alkyl group or an alkoxyl group, R1
Similarly, those having 1 to 12 carbon atoms are preferable.

R3 is an alkyl group or alkoxyl group having 1 to 20 carbon atoms, and like R1, one having 1 to 12 carbon atoms is preferable. m and n each represent an integer, and preferably (lIln) is 5 to 50,000, and preferably 20 to 50,000. A material with a high degree of polymerization has good nonlinear optical properties, and if (lll+n) is less than 5, it becomes difficult to solidify during molding. Further, the ratio of m and n may be appropriately set depending on the solubility in a solvent and the like. The molecular weight is preferably large enough to hold a π-conjugated polymer with high coating properties. X2 Xi is -S- or -NH-, respectively
shows. Note that each of R2 R3X2 Xi in the polymer represented by general II (II) does not need to be one type.

- π represented by formula (1) ~ The conjugated polymer may be either a random copolymer or a block copolymer.

These π-conjugated polymers may be used alone or in combination of two or more.

Next, −π − expressed by formula (1) or (It)
The synthesis method of conjugated polymers will be explained.

The synthesis method includes, but is not limited to, (Formula CI) and (It
) is used, such as a method of polymerizing a heptamer by electrolytically or chemically polymerizing it to give a polymerized unit represented by the formula. As a method for polymerizing by chemical polymerization, a synthesis method using an oxidizing agent such as ferric chloride as a catalyst is preferred because it is simple and increases the degree of polymerization.

The monomer providing the polymerized unit represented by formula (I) or (1) is a combination of a Grignard reagent such as R'' MgBr and 3
It can be obtained by a coupling reaction of a five-membered heterocyclic ring (thiophene or pyrrole) having a bromo group (B') in the nickel position using a nickel catalyst such as dichloro(diphenylphosphinopropane)nickel(I).

The π-conjugated polymer is soluble in a solvent.

Specific examples of the solvent for dissolving the π-conjugated polymer include dimethylformamide, dimethylacetamide, dimethylsulfoxide, dioxane, chloroform, tetrahydrofuran, dichloromethane, toluene, ethyl acetate, hexane, dimethoxyethane, xylene, nitropropane, Examples include organic solvents such as nitrobenzene, N-methylpyrrolidone, and benzonitrile.
Of course, it is not limited to these. These solvents may be used alone or in combination of two or more.

The organic nonlinear optical material of the present invention, which is made of the above-mentioned π-conjugated polymer, can be formed into a film, fiber, or bulk shape depending on the purpose. A thin film having a thickness of about 1,000 to 30,000 layers is preferable.

There are no particular restrictions on the method for forming a thin film of a π-conjugated polymer, but for example, by applying a solution of the π-conjugated polymer dissolved in the above-mentioned solvent onto a substrate, and then evaporating the solvent, the π-conjugated polymer can be formed into a thin film. - Can be made into a conjugated polymer thin film.

Examples of the coating method include a spin code method, a casting method, a dipping method, a bar code method, and a roll coating method. Among these, the spin code method is preferred from the viewpoint of producing a uniform thin film.

Such thin films are not only π-conjugated polymers useful as nonlinear optical materials, but also thin films without central symmetry, which is essential for second-order nonlinear optical effects, although the detailed cause is unknown. It becomes.

As described above, the organic nonlinear optical material of the present invention is an organic thin film in which π-conjugated polymers having a large molecular hyperpolarizability necessary for a second-order nonlinear optical material are oriented in a highly ordered manner. You can wander using simple methods such as the code method.

The present invention will be explained in more detail below using Examples, but the present invention is not limited thereto.

Example 1 Polyhexylthiophene in which R1 of general formula (I) is a hexyl group and Xi is an S atom was synthesized as follows.

First, 3.95 pieces of flaky metal magnesium were placed in the flask.
Hexylmagnesium bromide was obtained by a Grignard reaction in which 24 ml of hexyl bromide was added dropwise while stirring and 200 ml of diethyl ether. Next, in a flask were placed 20 g of bromothiophene, 0.33 g of dichloro(diphenylphosphinopropane)nickel (I[) as a catalyst, and 200 m of diethyl ether.
1 of hexylmagnesium bromide was added dropwise with stirring to cause a reaction, and after the dropwise addition was completed, reflux was further performed for 3 hours.

After the reaction was completed, diethyl ether was removed and purification was performed by distillation under reduced pressure to obtain 3-hexylthiophene.

8.4 g of the obtained 3-hexylthiophene monomer was
After dissolving in 00 ml of chloroform, 32.4 g of anhydrous ferric chloride was added as a catalyst, and the mixture was stirred at room temperature for 2 days under a nitrogen stream. After completion of the reaction, the obtained product was washed by Soxhlet extraction using acetone and methanol, dissolved in chloroform, and then reprecipitated into methanol to obtain polyhexylthiophene. The obtained polyhexylthiophene molecule ffl (My
) was examined by gel permeation chromatography and found to be 80,000.

Next, the temperature of the glass substrate and the ambient temperature were set to approximately 60°C.
An approximately 2% by weight chloroform solution of polyhexylthiophene was applied onto a glass substrate by spin coating and dried to form a film. At this time, the rotation speed of the spinner was 2000 revolutions per minute. The thickness of the film obtained was approximately 800.

The SHG characteristics of the obtained film were measured using the manufacturer's fringe method. The Maker fringe method is a method used to evaluate the nonlinear optical constant χ■ of a thin film material, and its χ0 is determined by comparing it with a standard sample (quartz single crystal). Also,
The sample can be rotated with respect to the incident light, the incident light and the output S
By setting the polarization of the H light to P polarization or S polarization, each component of the nonlinear optical constant tensor can be determined.

Figure 1 shows the experimental system used in this measurement. As shown in Figure 1, the laser beam with a wavelength of 1.08I emitted from the YAG laser (1) is converted into linearly polarized light by a polarizer (2), then focused by a lens (3), and placed on a rotating stage (4). A second harmonic is generated in the sample, the incident light is removed by a filter (6), the amount of light is adjusted to an appropriate level, and the polarizer (7) is used to polarize the desired polarized light S1.
Only one light is extracted and detected by a photomultiplier tube (8). In the figure, Cω is a boxcar integrator, and M is a controller.

Figure 2 shows the SHG manufacturer fringe of the film obtained. The horizontal axis is the rotation angle of the sample, and the vertical axis is the SHG light intensity generated at the sample. As shown in FIG. 2, manufacturer fringe peculiar to the thin film sample was observed, and it was found that the polyhexylthiophene spin cord film of Example 1 maintained vertical alignment with respect to the substrate. Although the cause of this is not clear at present, it is thought to be due to the inside of the material or the interaction between the material and the substrate.

Furthermore, the nonlinear optical constants of the obtained film are shown in Table 1.

Example 2 A polyhexylthiophene film was formed on a glass substrate in the same manner as in Example 1 using a chloroform solution containing about 2% by weight of polyhexylthiophene. However, the rotation speed of the spinner was 1000 revolutions per minute, and the thickness of the obtained film was about 1000 revolutions per minute. S of the obtained film
HG characteristics were measured in the same manner as in Example 1. Results first
Shown in the table.

Example 3 Chemical polymerization was carried out in the same manner as in Example 1 except that a mixture of the hexylthiophene monomer and thiophene monomer obtained in Example 1 at a molar ratio of 4:1 was used to obtain a polyhexylthiophene-polythiophene copolymer. I got a polymer.

The temperature of the glass substrate and the ambient temperature were set at about 80"C, and a solution of about 2% by weight of the copolymer in chloroform was applied onto the glass substrate by a spin code method and dried to form a film. At this time, , the rotation speed of the spinner is 20 per minute
It was set to 00 rotations. The thickness of the film was about 700 people. The SHG properties of the obtained film were measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative example 1 Table 1 shows the nonlinear optical constants of quartz single crystal.

Table 1 From Table 1, it can be seen that the nonlinear optical constants of the films of Examples 1 to 3 are much larger than that of quartz single crystal, which is an inorganic material.

[Effects of the Invention] As described above, the organic nonlinear optical material of the present invention is a material that has a high-performance second-order nonlinear optical effect, and has a solvent-soluble π
- Can be molded from conjugated polymers using a simple method.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a maker fringe measurement system for determining nonlinear optical constants, and FIG. 2 is a graph showing maker fringe characteristics of the polyhexylthiophene film obtained in Example 1. (Drawing symbols) (1): YAG laser (2): polarizer (3): lens (4) one-rotation stage (5): thin film sample (6): filter (7), polarizer (8): photoelectric Multiplier tube (9): Boxcar integrator (to) controller

Claims (1)

[Claims] (1) General formula (I): ▲Mathematical formulas, chemical formulas, tables, etc.▼(I) (In the formula, R^1 is an alkyl group or alkoxyl group having 1 to 20 carbon atoms, and X^1 is -S- or -NH-, l represents an integer) and/or general formula (II): ▲There are mathematical formulas, chemical formulas, tables, etc.▼(II) (In the formula, R^ 2 is a hydrogen atom or an alkyl group or alkoxyl group having 1 to 20 carbon atoms, and R^3 is a hydrogen atom to 1 to 2 carbon atoms.
0 alkyl or alkoxyl groups, X^2 and X
An organic nonlinear optical material having a second-order nonlinear optical effect, which is made of a π-conjugated polymer copolymer represented by -S- or -NH-, and m and n are integers.