JPH07333661A - Dyestuff compound for nonlinear optical material and nonlinear optical material contg. the same - Google Patents

Abstract

PURPOSE:To make it possible to obtain a nonlinear optical material having an extremely good nonlinear sensitivity and high performance by using specific dyestuff for the nonlinear optical material. CONSTITUTION:The dyestuff compd. for the nonlinear optical material is the dyestuff compd. expressed by the formula. In the formula, R<1> and R<2> respectively independently denote (substd.) lower alkyl groups and R<1> and R<2> may connect to each other to form a ring. R<3> denotes a hydrogen atom, (substd.) lower alkyl group or lower alkoxy group or denotes -NHCOR<4> group; R<4> denotes a lower alkyl group. The more specific examples of R<1> and R<2> include 1 to 6C alkyl groups or >=1 hydrogen atoms include hydroxyl groups, alkoxy groups, halogen atoms, amino groups, carbonyl groups, carboxyl groups or alkyl groups substd. with arom. rings (benzene rings, etc.). R<3> includes a methyl group, ethyl group, propyl group, etc.

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,
Letting E be the electric field (light or electrostatic field) applied from the outside, and P being the polarization of the substance induced thereby, P is expanded by E, and it can be expressed as the following formula (1).

[0003]

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

This χ⁽²⁾ Is quadratic, χ⁽³⁾ Is the third non-linear
Called shape susceptibility, these related phenomena are, for example,
Y. R. Shen "Principles of
Nonlinear Optics ”
It Currently used as a non-linear optical material
KDP (KH₂ PO _Four ), LiNbO₃ (niobium
Lithium acid), KTP (KTiOPO_Four ) Etc.
Mainly crystals 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 equation (2).

[0007]

## EQU00002 ## p = .mu. +. Alpha.E + .beta.EE + .gamma.EEE + ... (2)

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

[0016]

[Chemical 2](In the formula, R¹And R²Are each independently replaced
Represents a lower alkyl group which may be represented by R,¹And R
²May combine with each other to form a ring. R ³Is
Hydrogen atom, optionally substituted lower alkyl group
Is a lower alkoxy group, or -NHCOR^FourRepresents a group, R
^FourRepresents a lower alkyl group. )

The nonlinear optical material according to claim 2 is characterized by containing the dye compound according to claim 1. 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 compound for a nonlinear optical material of the present invention represented by the general formula (I), specific examples of R ¹ or R ² include an alkyl group having 1 to 6 carbon atoms, or one or more hydrogen atoms. Examples thereof include an alkyl group in which an atom is substituted with a hydroxyl group, an alkoxy group, a halogen atom, an amino group, a carbonyl group, a carboxyl group or an aromatic ring (benzene ring or the like). 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, a mono-form, such as a morpholine ring or a piperidine ring, in which R ¹ and R ² are linked to form a ring,
A piperazine ring, a tetrahydroxypyrrole ring and the like can also be mentioned. Specific examples of R ³ include a 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 and the like. The position at which R ³ is bonded may be either ortho or meta with respect to the alkylamino group.

By dissolving the dye compound of the present invention in a polymer, a polymer material containing the dye compound can be obtained. Any polymer material capable of dissolving the dye compound can be used as the polymer material capable of dissolving the dye compound, but it is preferable to use a material that gives a transparent film without scattering 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

By introducing a long-chain alkyl group into the dye compound of the present invention, a molecule capable of producing a Langmuir-Blodgett film can be obtained. Such a material is convenient as a second-order nonlinear optical material. Examples of such compounds include those having the dye of the present invention and an ester of a long-chain fatty acid represented by palmitic acid, stearic acid, arachidic acid, and behenic acid as R ¹ of the general formula (I). To be

This compound can be synthesized by the method represented by the following general formula. For details, see J. Chem. Soc. Perki
n Trans. I, 1975 (1990).

[0022]

[Chemical 3]

[0023]

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 (3).

[0024]

[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 such a relational expression, it is conceivable to increase the dispersion term representing the effect depending on the frequency of light in the expression (3). 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 compound represented by the general formula (1) is very excellent as a dye unit for a nonlinear optical material. . 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 poling 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 non-linear 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 an 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. Previous studies on polarized polymer compounds well explain the observed χ ⁽²⁾ , even in polymers heated to near the glass transition temperature, when such a distribution 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-optic 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.

Basically, the method for measuring the electro-optical effect used in the present invention is 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. The difference from the method of Ten et al. Is that 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. It's about to come. The relationship between the electro-optical coefficient r, χ ⁽²⁾ , and β to be obtained was as follows.

[0034]

[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. It should be noted that in order to be able to use the above formula (4), 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.

[0036]

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

[0037]

[Chemical 4]

A cyclopentanone solution in which the dye represented by the above structural formula and polymethylmethacrylate (manufactured by Aldrich, medium molecular weight, intrinsic viscosity 0.45, abbreviated as "PMMA") are dissolved is spin-coated, Film thickness 30
A film having a thickness of about 1 to 3 μm was formed on the ITO electrode of 0 Å. The dye concentration in PMMA was adjusted to 5% by weight. After drying at 130 ° C for 1 hour to remove the solvent,
Gold was vacuum deposited to a thickness of 1000Å. The molecular hyperpolarizability β was measured by the method described in the above section using the light of a semiconductor laser of 1.31 μm. The heating for poling was performed at 120 ° C. for 10 minutes, and the applied electric field was a DC voltage such that the DC electric field was 0.5 MV / cm, with an AC voltage of 10 Vrms superposed. The obtained result shows that the μβ product is 3330 × 10 ⁻⁴⁸ es
It was u.

Example 2

[0040]

[Chemical 5]

A cyclopentanone solution in which the dye represented by the above structural formula and PMMA are dissolved is spin-coated, and an ITO electrode having a thickness of 300 Å is provided with a film thickness of about 1 to 3 μm.
The film of was produced. The dye concentration in PMMA was adjusted to 4% by weight. After drying at 130 ° C. for 1 hour to remove the solvent, gold was vacuum-deposited to a thickness of 1000Å.
The molecular hyperpolarizability β was measured by the method described in the above section using the light of a semiconductor laser of 1.31 μm. The heating for poling is 10 at 120 ° C.
The applied electric field is 0.5 MV / c
An alternating current voltage of 10 Vrms was superimposed on a direct current voltage of m. The obtained result shows that the μβ product is 368.
It was 0 × 10 ⁻⁴⁸ esu. Comparative Example 1

[0042]

[Chemical 6]

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

[0044]

[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 was used. The heating condition at that time was 110 ° C. for 10 minutes, and the applied voltage was 100 V DC and 20 V _rms AC was superimposed. The μβ product obtained was 550 × 10 ⁻⁴⁸ esu.

[0046]

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.

[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 compound represented by the following general formula (I):
And a dye compound for a nonlinear optical material. [Chemical 1](In the formula, R¹And R²Are each independently replaced
Represents a lower alkyl group which may be represented by R,¹And R
²May combine with each other to form a ring. R ³Is
Hydrogen atom, optionally substituted lower alkyl group
Is a lower alkoxy group, or -NHCOR^FourRepresents a group, R
^FourRepresents a lower alkyl group. ) 2. A non-linear optical material comprising the dye compound according to claim 1. 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.