JPH06317821A - Dyestuff for nonlinear optical material and nonlinear optical material containing the same - Google Patents

Abstract

PURPOSE:To improve nonlinear sensitivity and to form an element exhibiting high performance by using a specific dyestuff compound for nonlinear optical material to obtain a dyestuff large in molecular hyper polarizability. CONSTITUTION:The dyestuff for nonlinear optical material is expressed by a formula. In the formula, each of R<1> and R<2> is individually -CN or -CONH2 and at least one of R<1> and R<2> is -CN, each of R<3> and R<4> is individually hydrogen atom or (substituted)lower alkyl group, each of R<5> and R<6> is individually hydrogen atom, lower alkyl group, alkoxyl group or acylamino group. The dyestuff having the structure in this manner is dissolved into a polymer to obtain a polymer material containing the compound. Though anything uniformly dissolving is used as the polymer material for dissolving, one free from scattering and capable of giving a transparent film is preferably used for the optical material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dye for a nonlinear optical material and a nonlinear optical material containing the same, and particularly to a dye suitably used for providing a material having a large second-order nonlinear susceptibility. And a non-linear optical material including the same, which is effective as a light control element used for an electro-optical light modulation element, a wavelength conversion element, or the like.

[0002]

2. Description of the Related Art Non-linear optical materials are widely used for conversion and control of light, particularly laser light, such as wavelength conversion of light, modulation of light by change in refractive index, switching and the like. This is understood as a phenomenon caused by the nonlinear polarization of a substance due to an electromagnetic field applied from the outside. here,
When the electric field (light or electrostatic field) applied from the outside is E, and the polarization of the substance induced by it is P, and P is expanded by E, it can be expressed as the following formula (2).

[0003]

[Equation 1] P = P ₀ + χ ⁽¹⁾ E + χ ⁽²⁾ EE + χ ⁽³⁾ EEE + ... (2)

This χ⁽²⁾ Is quadratic, χ⁽³⁾ Is the third non-linear
Called shape susceptibility, these related phenomena are, for example,
Y. R. “Principles of N” by Shen
online optics ".
Currently used as a non-linear optical material
Is KDP (KH₂ PO _Four ), LiNbO₃ (Niobic acid
Lithium), KTP (KTiOPO_Four ) Single oxide
Mainly crystalline and semiconductor materials such as GaAs.

In recent years, π-electron conjugated organic compounds have been attracting attention as this nonlinear optical material. This is because its nonlinear susceptibility is much higher than that of inorganic materials and it is derived from electronic polarization, so when it is applied to all-optical devices, it has an ultra-fast response time of picoseconds or less. It depends on what is expected. In addition, it has a low dielectric constant, is more resistant to optical damage than lithium niobate, etc., the manufacturing method is easier for polymer materials than single crystal growth, and various functions are possible due to various molecular designs. There is a possibility of adding the above-mentioned reason as another reason why the organic material is expected as a nonlinear optical material. By utilizing the features of such organic compounds, it is possible to fabricate wavelength conversion elements such as second harmonic generation for low power lasers such as semiconductor lasers, and electro-optical modulation elements that are driven at low voltage and have high speed response. It is possible.

Various forms of organic materials have been investigated as actual organic materials as nonlinear optical materials. In organic compounds, nonlinear susceptibility is discussed in terms of molecular hyperpolarizability.
When the electric field acting on the molecule is E and the dipole moment of the molecule induced by this is p, it can be expressed by the following formula (3).

[0007]

## EQU00002 ## p = .mu. +. Alpha.E + .beta.EE + .gamma.EEE + ... (3)

Here, α is called a molecular polarizability, β and γ are called second-order and third-order molecular hyperpolarizabilities, respectively, and the nonlinear susceptibility of a molecular assembly is derived from these β and γ. As the secondary nonlinear optical material, an intramolecular charge transfer material containing an electron-donating group and an electron-withdrawing group in the molecule and linked by a π-electron conjugated system is a secondary molecule. It has been shown that the hyperpolarizability (β) becomes large, and most of the known organic compounds showing a large χ ⁽²⁾ , such as methylnitroaniline (MNA), have It is a type of molecule.

However, the second-order nonlinear optical material has a limitation that its structure has no macroscopic inversion symmetry. That is, since χ ⁽²⁾ is the third-order tensor, β
Χ ⁽²⁾ is 0 when the aggregate has a crystal structure with inversion symmetry or is amorphous even if is large. Therefore, how to orient a molecule having a large β in a polar structure is a major issue in material search.

In this organic nonlinear optical material, it is the most common practice to utilize the crystal structure,
The powder SHG method is a method for easily screening such materials. In the past, some ideas for molecular design such as introduction of an optically active group, a skeleton with a small dipole moment in the ground state, and the use of hydrogen bond have been proposed in order to obtain a crystal in which the molecule has an optimal arrangement.

However, the effect is not clear unless the crystal is finally obtained. Further, the crystal of the organic compound is a molecular crystal and is soft and poor in processability. Furthermore, it is often desirable to process into a waveguide structure when it is put to practical use as a nonlinear optical element, but the thin film forming method, control of crystal orientation, and method of partially changing the refractive index are very necessary for this. It's difficult. From such a fact, although the possibility of a large number of organic crystals as a nonlinear optical material has been investigated, it is the present situation that only a few examples are processed into elements.

Another secondary organic non-linear optical material is a polymer material. This is an acrylic polymer doped with a large β molecule represented by Disperse Red 1 (N-ethyl-N-hydroxylethyl-4-amino-4′nitroazobenzene: see Comparative Example 1 below). Or, it is represented by a compound bonded to a side chain of a polymer. It is known that a polymer material can be easily formed into a thin film by coating and becomes an optically excellent optical waveguide material, but a film just coated is generally amorphous and χ ⁽²⁾ is 0. As a method for showing χ ⁽²⁾ , a polymer film is heated to a temperature not lower than the glass transition temperature Tg while applying an electric field to orient a unit having a large β, and then cooled to room temperature. The operation called boring for fixing the orientation is most often used, and a material exhibiting an electro-optical effect comparable to that of lithium niobate is obtained. However, the biggest drawback of this procedure is that its orientation is thermally relaxed and χ ⁽²⁾ is gradually attenuated.

In addition, as a method of obtaining a structure in which a unit having a large β is oriented, it has been attempted to use an oriented film such as a Langmuir-Blodgett film. Large χ ^{(2) for} any nonlinear optical material
The material with has many advantages for making the device highly efficient. For example, in an optical switch element utilizing the electro-optical effect, if a material having a large electro-optical effect is used, a low voltage drive type can be obtained and the length of the element can be shortened, which is advantageous for integration. Further, the dielectric constant of the organic material is about 3 to 4, which is 1 / th that of lithium niobate.
Since it is about 10, it is possible in principle to operate at about 10 times as high speed, which is advantageous for application to the field of high-speed optical communication.

[0014]

As described above, in order to obtain a device with high characteristics, it is necessary to develop a nonlinear optical material having a high nonlinear susceptibility. Conventionally, such a nonlinear optical material has been provided. The current situation is that it has not been done. The present invention has been made in view of the above conventional circumstances, and provides a dye having a large molecular hyperpolarizability β that can be used to obtain a material having a large nonlinear susceptibility, thereby significantly increasing the nonlinear susceptibility. An object of the present invention is to provide a non-linear optical material capable of producing an element exhibiting higher performance than conventional elements.

[0015]

The dye for nonlinear optical material according to claim 1 is characterized by being represented by the following structural formula (1).

[0016]

[Chemical 2] (In the formula, R ¹ and R ² are each independently —CN or —C.
Represents ONH _2, and at least one of R ¹ and R ² is-
CN, R ³ and R ⁴ each independently represent a hydrogen atom or an optionally substituted lower alkyl group, and R ⁵ and R ⁶ each independently represent a hydrogen atom, a lower alkyl group or an alkoxy group. Alternatively, it represents an acylamino group. )

The non-linear optical material according to a second aspect is characterized by containing the dye compound according to the first aspect and imparting a structure having no inversion symmetry. The nonlinear optical polymer material according to claim 3 is the nonlinear optical material according to claim 2, wherein the polymer contains the dye compound according to claim 1, and an electric field is applied to the dye while heating the dye compound. It is characterized by being obtained by orienting a compound.

The present invention will be described in detail below. In the dye for a nonlinear optical material of the present invention represented by the structural formula (1), R ¹ and R ² are each independently —CN or —CO.
Represents NH _2, and at least one of R ¹ and R ² is -C
Represents N, R ³ and R ⁴ each independently represent a hydrogen atom or an optionally substituted lower alkyl group, and R ⁵ and R ⁶ each independently represent a hydrogen atom, a lower alkyl group or an alkoxy group. Alternatively, it represents an acylamino group.

Particularly, in the structural formula (1), R ¹ and R ² are each independently --CN or --CONH ₂ .
At least one of R ¹ and R ² is —CN, and R ³
And R ⁴ is a lower alkyl group, R ⁵ is a hydrogen atom, a lower alkyl group or —NHCOR ⁷ (R ⁷ represents a lower alkyl group), and R ⁶ is a hydrogen atom.

Specific examples of R ³ and R ⁴ include an alkyl group having 1 to 6 carbon atoms, a hydroxyl group, an alkoxy group, a halogen atom, an amino group, a carbonyl group, a carboxyl group, an aromatic ring such as a benzene ring. And an alkyl group in which one or more hydrogen atoms are substituted with. More specifically, methyl group, ethyl group, propyl group (n, i), butyl group (n, i, t), pentyl group, hexyl group, hydroxymethyl group, hydroxyethyl group, hydroxypropyl group, methoxyethyl group. Group, acetoxyethyl group, acryloxyethyl group, methacryloxyethyl group, phenoxyethyl group, toluenesulfonyloxy group, aminomethyl group, aminoethyl group, benzyl group, fluoroethyl group, chloroethyl group, bromoethyl group, iodoethyl group, etc. Can be mentioned. Further, examples thereof include a ring formed by R ³ and R ⁴ , such as a morpholine ring, a piperidine ring, a piperazine ring, and a tetrahydroxypyrrole ring.

More specific examples of R ⁵ and R ⁶ include:
Methyl group, ethyl group, propyl group (n, i), butyl group (n, i, t), pentyl group, hexyl group, methoxy group, ethoxy group, propyloxy group (n, i), butyloxy group (n, i, t), acetamino group, propionylamino group, butyrylamino group and the like.

If a dye having this structure is dissolved in a polymer, a polymer material containing this compound can be obtained. Any polymer material that can be dissolved may be used as long as it dissolves uniformly, but a material that gives a transparent film without scattering is desirable for use as an optical material. Examples thereof include methacrylic resin, acrylic resin, polycarbonate resin, styrene resin, urea resin, phenol resin, polyamide resin, polyester resin, polyimide resin, epoxy resin, silicone resin, polyvinyl chloride, and copolymers and blends thereof. To be

Further, by introducing a long-chain alkyl group, a molecule capable of producing a Langmuir-Blodgett film can be obtained. Such a material is convenient as a second-order nonlinear optical material. As examples of such things, the dye of the present invention and palmitic acid, stearic acid,
Examples thereof include those having an ester of a long-chain fatty acid represented by arachidic acid and behenic acid in R ³ and R ⁴ .

Such a dye for a nonlinear optical material of the present invention can be prepared, for example, by the following general formula (4) (wherein R ¹ , R ² ,
R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ have the same meaning as defined above. ). The details of the reaction are described in J. Chem. Soc. Perkin Trans.
1, 439 (1988).

[0025]

[Chemical 3]

The non-linear optical material of the present invention containing such a dye for non-linear optical material can be easily produced, for example, according to the method of Example 1 described later. In producing the nonlinear optical material according to the third aspect, as the polymer containing the dye for nonlinear optical material, acrylic or methacrylic polymer can be preferably used.

[0027]

FUNCTION The molecular hyperpolarizability β in the two-level model considering only the ground state and the excited state having a large contribution is expressed by the following equation (5).

[0028]

[Equation 3]

Here, μ ₀₁ is the transition moment from the ground state to the excited state, Δμ is the difference between the dipole moments of the ground state and the excited state, ω ₀ is the frequency corresponding to the energy difference between the ground state and the excited state, ω represents the frequency of the relevant light.
Most organic nonlinear optical materials have an intramolecular charge transfer property in which an electron-donating group and an attracting group are conjugated with π electrons in the molecule, and a large transition moment and dipole moment It is understood as the origin of polarization.

In order to further increase β in the above relational expression, it is conceivable to increase the dispersion term in the expression (4), which represents the effect depending on the frequency of light. This corresponds to making the light absorption frequency ω ₀ close to the light absorption frequency ω ₀ and increasing the denominator of the dispersion term. This is a phenomenon generally known as the resonance effect. However, when the frequency of light approaches the frequency of molecular absorption, absorption of light also begins to occur because the width of the absorption spectrum is finite. Since the nonlinear optical effect is generally a small effect, it is necessary to propagate light over a certain distance in order to use it, and the absorption of molecules limits this. Therefore, it is impossible to approach the resonance frequency unnecessarily. In order to use it as an electro-optical element for optical communication, the wavelength of light used, for example, 1.3 μm or 1.5
The absorption must be sufficiently small in μm. In consideration of the above, the inventors of the present invention have found that the molecule shown below is very excellent as a dye unit for a nonlinear optical material.

[0031]

[Chemical 4]

When a dye having this structure is contained in a polymer, a polymer material containing this compound can be obtained. Moreover, by introducing a long-chain alkyl group, a molecule capable of producing a Langmuir-Blodgett film can be obtained. Such a material is effective as a second-order nonlinear optical material.

This molecule has an electron-donating group and an electron-withdrawing group conjugated with π electrons in the molecule and is a very strong intramolecular charge transfer type compound. Further, the absorption is also in the long wavelength region, and it exhibits a large nonlinear hyperpolarizability even for light in the near infrared region used for optical communication. However, at 1.3 μm or 1.5 μm used for optical communication, the absorption is sufficiently small, and it is possible to fabricate a device suitable for these.

In order to use the dye compound of the present invention represented by the structural formula (1) as a second-order nonlinear optical material, it is necessary to orient the molecules in a polar structure. For this purpose, a so-called bowling method can be used in which the polymer containing the dye is oriented by heating it near the glass transition temperature Tg while applying an electric field. In addition, the Langmuir-Blodgett method can also be used in which both a hydrophilic group and a hydrophobic group are provided, a monomolecular film is formed on the water surface, and this is transferred to a substrate to obtain an alignment film. Furthermore, by directly or by introducing an appropriate substituent into the present dye compound,
If a crystal that does not have inversion symmetry can be obtained, it becomes a material that exhibits extremely high nonlinearity. By utilizing the large hyperpolarizability β of the present dye compound, a very excellent nonlinear optical material can be obtained by whatever method the polar structure is obtained.

The thus obtained nonlinear optical material containing the dye compound of the present invention can be used as a material for producing an optical modulator or an optical switch element by utilizing its electro-optical effect. Further, if an appropriate wavelength is selected, it can be applied to a wavelength conversion element such as sum, difference frequency generation, parametric amplification and oscillation including second harmonic generation. By the way, the electric field induced second harmonic generation method (EFISH method) is often used to measure the molecular hyperpolarizability, but this method is difficult for a dye that strongly absorbs the light of the second harmonic wave. Therefore, in the present invention, the following method is used.

Generally, the nonlinear susceptibility χ ⁽²⁾ obtained from the measurement of the nonlinear optical effect is the average of the molecular hyperpolarizabilities β in the distribution of molecular orientation. In the EFISH method, this is represented by the distribution of orientation in the electric field of the dipole that can rotate freely. From previous studies of polarized polymer compounds, even in polymers heated to near the glass transition temperature, such distributions are well explained for observed χ ⁽²⁾ when the orientation ratio is small. It has been reported that However, especially in a system in which a dye molecule is simply dissolved in a polymer, orientation relaxation occurs rapidly even at room temperature, and the orientation cannot be estimated.

In the present invention, the DC voltage applied for orientation was left as it was, and the AC voltage was superimposed on it to measure the electro-optical effect. As a result, relaxation after orientation does not occur, and the degree of orientation can be expected to be maintained when the mobility of the polymer is frozen. However, the orientation is gradually frozen as the temperature is lowered, and it is difficult to define a constant orientation temperature. However, even when oriented at 100 to 120 ° C. and lowered to room temperature as conducted in the study of the present invention, this temperature is between the heating temperature and room temperature, and this effect is 300/393 = 0. Since it is within 76, even if the heating temperature is used, it is sufficient as a dye evaluation method.

The measuring method of the electro-optical effect used in the present invention is basically C.I. C. Ten et al., Appl. Ph
ys. Lett. 56, p1734 (1990). The layout of a specific experiment is shown in FIG. In FIG. 1, reference numeral 1 is a laser, 2 is a polarizer, 3 is a compensator for papinesoleil, 4 is an analyzer, 5 is a photodiode, 6 is a lock-in amplifier, 7 is a power supply, 8 is a sample,
9 is a heater, 10 is an electrode, and 11 is a temperature controller.
Here, C.I. C. Different from Ten et al., The sample is fixed to the heat block, the temperature can be controlled by the temperature controller, and the applied voltage can be offset from AC to DC. By the way. Required electro-optic coefficient r and χ
⁽²⁾ The relation with β was as follows.

[0039]

[Equation 4]

Here, n is the refractive index, N is the number density of the dye, and f
(W) is a local field correction coefficient of light or electric field of frequency w, θ is an angle formed by the dipole μ of the molecule with the electric field, <> is an average, E is an electrostatic field applied from the outside, k is a Boltzmann constant, T Represents temperature. f (w) was described by Singer et al. Chem. Ph
ys. 75, p3572 (1981). Thus, the μβ product is obtained from the measurement of r. The electro-optic coefficient obtained by this measurement method depends on the χ ⁽³⁾ effect due to the DC electric field, that is, the Kerr effect, the change in the refractive index due to the molecular orientation in the polymer due to the electric field at room temperature, and the electric field orientation of the polymer matrix itself. Although there are contributions from the electro-optic effect, etc., the effect is not so large in general, and can be sufficiently used to compare at least relative μβ products. In order to be able to use the above formula (6), it is considered desirable to make the applied voltage and the concentration of the dissolved dye as small as possible. Also, for molecules that have strong intermolecular interactions even at low concentrations and tend to be antiparallel,
The required μβ product is smaller than the actual μβ, and for molecules where the molecules tend to be parallel, the required μβ
The β product becomes larger than the actual one, but such interaction is important as a dye for nonlinear optics, and the required μβ product corresponds to the actually obtained effective value.

[0041]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. Example 1

[0042]

[Chemical 5]

A cyclopentanone solution in which a dye represented by the above structural formula (7) and polymethylmethacrylate (PMMA, manufactured by Aldrich, medium molecular weight, intrinsic viscosity 0.45) was dissolved was spin-coated to give a film thickness of 2 A 0.5 μm film was prepared on a 300 Å ITO electrode. The dye concentration in the film was set to 5% by weight. 130 ° C
After drying for 1 hour to remove the solvent, gold was vacuum deposited to a thickness of 1000Å. Using the light of a semiconductor laser of 1.31 μm, β was measured by the method described in the above-mentioned action section. The heating conditions are 100 ° C. for 10 minutes and 1
Comparison was made at 20 ° C. for 10 minutes, but it was confirmed that similar results were obtained. The applied voltage is DC voltage 25
The AC voltage of 10 to 30 Vrms superimposed on -100 V was used.

It was confirmed that the signal obtained in this applied voltage range was linear as shown in FIG. Also,
The frequency of the applied alternating current was 70 Hz to 10000 Hz with the same result. This result means that non-linearity proportional to the boring voltage appears, and the validity of the equation (6) was confirmed.

From these results, 1 is observed.
It can be seen that the phenomenon, which is the following electro-optical effect and which hinders measurement such as saturation, does not occur within the range of applied voltage. The obtained result shows that the μβ product is 5000 × 10 ⁻⁴⁸ es
It was u. The absorption spectrum of the film used above is shown in FIG. From FIG. 3, it can be seen that the absorption at 1.3 μm is sufficiently small.

For further investigation, this dye-containing P
Light propagation experiments on MMA films were performed. That is, PMMA in which 10% by weight of the dye represented by the formula (7) is dissolved
Was coated on a 0.75 μm period grating made of fused silica, and the incident angle of the laser light of 1.31 μm was adjusted to combine the two. As a result, it was confirmed that the light propagation was observed over at least 1 cm, and the absorption at 1.31 μm was weak. Example 2

[0047]

[Chemical 6]

The μβ product was measured in the same manner as in Example 1 except that the dye represented by the structural formula (8) was used as the dye. The obtained μβ product is 7700 × 10 ⁻⁴⁸ e
It was su. Example 3

[0049]

[Chemical 7]

The μβ product was measured in the same manner as in Example 1 except that the dye represented by the above structural formula (9) was used. The obtained μβ product is 7400 × 10 ⁻⁴⁸ e
It was su. Example 4

[0051]

[Chemical 8]

The μβ product was measured in the same manner as in Example 1 except that the dye represented by the above formula (10) was used. The obtained μβ product is 4200 × 10 ⁻⁴⁸ es
It was u. Comparative Example 1

[0053]

[Chemical 9]

The μβ product was measured in the same manner as in Example 1 except that the dye was Disperse Red 1 (Aldrich Co.) represented by the above structural formula (11). The heating condition at that time was 110 ° C. for 10 minutes, and the applied voltage was 100 V DC and 20 V rms alternating current. The μβ product obtained was 1100 × 10 ⁻⁴⁸ esu. Comparative example 2

[0055]

[Chemical 10]

Μβ was obtained in the same manner as in Example 1 except that the dye had a structure represented by the above formula (12).
Product measurements were taken. The heating conditions at that time are 110 ° C and 1
At 0 minutes, the applied voltage was 100 V DC and 20 V rms AC superimposed. The obtained μβ product is 545 × 10
It was ^-48 esu.

[0057]

As described in detail above, the dye for non-linear optical material of the present invention has a remarkably high molecular hyperpolarizability β, and according to the non-linear optical material of the present invention using such a dye for non-linear optical material, A high-performance non-linear optical material having a remarkably good non-linear susceptibility is provided. Particularly, according to the non-linear optical material of claim 3, a non-linear optical material that is easy to manufacture and has excellent functionality and versatility is provided. Such a non-linear optical material of the present invention is used as an electro-optical light modulator, a wavelength conversion element, or the like, as a non-linear optical material for controlling light.
It is extremely useful industrially.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus used for measuring an electro-optical effect in the present invention.

2 (a) is a graph showing the dependence of the electro-optic coefficient observed in Example 1 on the applied DC voltage, and FIG. 2 (b) is the electro-optic observed in Example 1; It is a graph which shows the dependence of the modulation signal by an effect on the applied alternating voltage.

FIG. 3 is a graph showing an absorption spectrum of the film manufactured in Example 1.

[Explanation of symbols]

 1 Laser 2 Polarizer 3 Papine Soleil Compensator 4 Analyzer 5 Photodiode 6 Lock-in Amplifier 7 Power Supply 8 Sample 9 Heater 10 Electrode (ITO and Gold) 11 Temperature Controller

Claims (3)

[Claims] 1. A dye compound for a nonlinear optical material represented by the following structural formula (1). [Chemical 1] (In the formula, R ¹ and R ² are each independently —CN or —C.
Represents ONH _2, and at least one of R ¹ and R ² is-
CN, R ³ and R ⁴ each independently represent a hydrogen atom or an optionally substituted lower alkyl group, and R ⁵ and R ⁶ each independently represent a hydrogen atom, a lower alkyl group or an alkoxy group. Alternatively, it represents an acylamino group. ) 2. A dye compound according to claim 1 is contained,
A non-linear optical material provided with a structure having no inversion symmetry. 3. The non-linear optical material according to claim 2, wherein the dye compound according to claim 1 is contained in a polymer, and an electric field is applied while heating to orient the dye compound. Nonlinear optical polymer materials.