JPH055915A - Nonlinear optical material - Google Patents

Abstract

PURPOSE:To provide the nonlinear optical material having a large nonlinear optical constant useful for wavelength conversion of light, etc. CONSTITUTION:This nonlinear optical material is constituted of cholesteric liquid crystalline polypeptide and a compd. which has >=10<-30>esu quadratic nonlinear molecular sensitivity and exhibits nonlinear optical response. The content of the former of this material is >=10wt.% and <50wt.% and the content of the latter is over 50wt.% and 90wt.% or below. The non linear optical material has the high nonlinear sensitivity, exhibits high SHG activity and is stable in the performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel nonlinear optical material having a large nonlinear optical constant useful for wavelength conversion of light.

[0002]

BACKGROUND OF THE INVENTION Nonlinear optical materials have been actively studied as a core technology for a wide range of optoelectronics including wavelength conversion elements for laser light, optical modulation elements, optical switches, and optical computers. .. As a non-linear optical material, lithium niobate or potassium dihydrogen phosphate is well known. Compared with these inorganic materials, organic nonlinear optical materials have excellent characteristics such as nonlinear optical constants that are 100 to 1000 times larger, high-speed response, and resistance to optical damage. Nevertheless, a crystal having a large second-order molecular susceptibility sufficient for practical use has not been obtained in reality.

In many cases, even if the constituent molecule itself has a large second-order molecular susceptibility, the second-order electric susceptibility becomes 0 due to the inversion symmetry in the crystalline state, resulting in No optical second harmonic (SHG) is generated. As described above, it is difficult to produce a single crystal having no symmetry center by using the organic low molecular weight compound alone. Therefore, the high molecular weight compound is used as a matrix to disperse these organic molecules,
There has been proposed a method of orienting a host polymer with the help of an external field such as an electric field and at the same time asymmetrically orienting a guest organic molecule.

For example, in a nematic liquid crystal polymer, 4-
Dimethylamino-4'-nitrostilbene (DANS)
There is an example of observing SHG by applying an electric field to orient the guest and the host after mixing the [G. R. Meredith, Macromoleculars, 15 (5) , 1385 (1982)]. However, in this example, due to the fact that DANS was mixed in at most 2% and the orientation force of the host polymer liquid crystal was insufficient, only an insufficient nonlinear optical constant of about several times that of urea was obtained. Absent.

In Japanese Patent Laid-Open No. 62-238538, a thin film of a composition in which DANS is dispersed in a main chain type thermotropic liquid crystal is irradiated with an Nd ³⁺ / YAG laser to produce an SH of 0.53 μm.
An example of observing G is described. In addition, JP-A-62-24360
No. 4 synthesizes a side chain type liquid crystalline polymer in which a unit showing a mesogen and a nonlinear optical response is bonded to the side chain of a polymer exemplified by polyacrylate, polymethacrylate, polysiloxane, etc., and a film of this polymer is synthesized. After orientation by applying an electric field to the substrate, Nd ³⁺ / YAG laser light was made incident to observe SHG of 0.53 μm.

The methods described in these documents have a common feature that the matrix polymer used for asymmetrically orienting the unit exhibiting a nonlinear optical response has a nematic liquid crystallinity, and therefore is put to practical use. There is a serious drawback in that it is not possible to obtain a material with a nonlinear optical constant as large as possible. Another drawback of the method using a nematic liquid crystal polymer is that there is no advantage of using a nematic liquid crystal in phase matching, which is an important technology for practical use, and a method using ordinary birefringence or an optical waveguide is used. You have to rely on how to use.

On the other hand, a method using polyethylene oxide having no liquid crystallinity as a matrix polymer has been proposed [Miyata et al., Polymer Preprints, Japan Vol. 36, No.
8,2523 ('87)]. Miyata et al. P in polyethylene oxide
-By dispersing nitroaniline and crystallizing polyethylene oxide while applying an electric field, 90 times as much SHG as urea is generated. However, as stated by Miyata et al., The strength of this SHG is about 10%. There is a problem that it begins to decrease after an hour, and after 40 hours it drops to 10% of MNA (2-methyl-4-nitroaniline).

[0008]

[Means for Solving the Problems] A serious drawback of the conventional method in which a polymer compound and a compound exhibiting a nonlinear optical response are mixed and an electric field is applied to the mixture to develop a nonlinear optical effect, that is, SHG activity is As a result of intensive studies conducted by the present inventors with the aim of solving the drawback of low or very short lifetime, the present inventors have used a polypeptide exhibiting cholesteric liquid crystallinity, which has a non-linear molecular susceptibility. It has been found that by blending a compound having a large ratio, a nonlinear optical material having a large nonlinear optical constant and exhibiting stable and high level SHG activity can be obtained.

That is, the nonlinear optical material according to the present invention is a nonlinear optical material comprising a mixture of a polypeptide and a compound exhibiting a nonlinear optical response, wherein the polypeptide exhibits cholesteric liquid crystallinity and exhibits a nonlinear optical response. The second-order nonlinear molecular susceptibility of the compound shown is 10 ⁻³⁰
It is characterized in that the mixture is not less than esu and the mixture is composed of 10% by weight or more and less than 50% by weight of a polypeptide and a compound having a nonlinear optical response of more than 50% by weight and 90% by weight or less.

The present invention will be described in more detail below. Any polypeptide can be used in the present invention as long as it exhibits cholesteric liquid crystallinity.
Therefore, as the polypeptide, for example, alanine, aminoadipic acid, aminobutyric acid, aminocaproic acid, aminocyclopentanoic acid, aminovaleric acid, aminomalonic acid, arginine, asparagine, aspartic acid cysteine, glutamic acid, glycine. , Histidine, homocysteine, isoleucine,
In addition to homopolymers such as leucine, lysine, methionine, norvaline, ornithine, phenylalanine, serine, threonine, tyrosine, valine, proline, and copolymers thereof, the homopolymers of various derivatives of the amino acids exemplified above can be used. Mention may be made of polymers and copolymers.

Preferred polypeptides include, for example:
Examples thereof include homopolymers and copolymers of glutamic acid, aspartic acid, oxyglutamic acid, etc., and homopolymers and copolymers of the above-mentioned amino acid ester derivatives. Among them, a polypeptide having a structure represented by the following chemical formula 1, that is, a polymer of glutamic acid ester and aspartic acid ester is particularly preferable.

[0012]

[Chemical 1]

In the above chemical formula 1, R is a carbon number of 1 to 30.
Represents an alkyl group, a cycloalkyl group, an aryl group or an arylalkyl group, and m is 10 ≦ m ≦ 200
0 and n are 1 or 2.

The alkyl group represented by R is a methyl group,
Ethyl group, propyl group, isopropyl group, butyl group, pentyl group, hexyl group, octyl group, decyl group, dodecyl group, octadecyl group, hexadecyl group, eicosanyl group and those with the same branched carbon number Of these, a methyl group, an ethyl group, a propyl group, a butyl group, a branched butyl group, a hexyl group, a decyl group, a dodecyl group, and an octadecyl group are particularly preferable.

As the cycloalkyl group, a cyclopentyl group, a cyclopentylmethyl group, a methylcyclopentyl group, an ethylcyclopentyl group, a butylcyclopentyl group, a cyclohexyl group, a methylcyclohexyl group,
Ethylcyclohexyl group, butylcyclohexyl group, cyclohexylmethyl group, cyclohexylethyl group, cyclohexylpropyl group, cyclohexylbutyl group, cyclooctyl group, methylcyclooctyl group, cyclododecyl group and the like are preferable, and among them, cyclopentyl group, cyclohexyl group, cyclopentyl group. A methyl group and a cyclohexylmethyl group are particularly preferable.

As the aryl group, phenyl group, toluyl group, dimethyltoluyl group, butylphenyl group, decylphenyl group and dodecylphenyl group are used. Examples of the arylalkyl group include benzyl group, methylbenzyl group, phenylethyl group, methylphenylethyl group, phenylpropyl group, phenylbutyl group, phenylhexyl group, phenyloctyl group, phenyldodecyl group, methylphenylbutyl group, ethylphenylhexyl group. A group, a methylphenyldodecyl group, a biphenylmethyl group and the like are preferable, and above all, a benzyl group, a methylbenzyl group, a phenylethyl group, a phenylbutyl group and a biphenylmethyl group are particularly preferable.

When R is an aryl group or an arylalkyl group, a part of hydrogen atoms in the aromatic ring is halogen such as fluorine, chlorine and bromine, polar group such as methoxy group, cyano group, hydroxyl group and amino group. It can be replaced with. In addition, the polypeptide having the structure represented by the above chemical formula 1 includes a copolymer of two or more kinds of esters having different R types. Furthermore, not only those having a peptide bond at the α-position but also those at the β-position or the γ-position can be used as the polypeptide of the present invention.

M in Chemical formula 1, that is, the degree of polymerization is 10 to
It is 2000, preferably 30 to 1500. When the degree of polymerization is less than 10, sufficient SHG activity cannot be obtained, and when the degree of polymerization is more than 2000, the SHG activity is also decreased and the moldability is deteriorated, which is not preferable.

In the present invention, both naturally occurring polypeptides and synthetic polypeptides can be used. By the way, when synthesizing a desired polypeptide, a method by the NCA method known in the art can be adopted. That is, N-carboxylic acid anhydride (NCA) of a predetermined amino acid or a derivative of an amino acid,
N- of derivatives such as glutamic acid γ-esters
It can be synthesized by homopolymerizing or copolymerizing a carboxylic acid anhydride.

Next, a compound (abbreviated as NLO compound) showing a nonlinear optical response, which is another important component constituting the nonlinear optical material of the present invention, will be described. The polarization μ generated when an external electric field (for example, light) of E is applied to the organic compound is represented by μ = αE + βE · E + γE · E · E +. In this equation, α, β, γ ... Are each 1
The secondary, secondary, tertiary ... molecular susceptibility, and the NLO compound used in the present invention has a secondary molecular susceptibility β of 1 × 10.
^-30 esu or more, preferably β is 10 ×
It is larger than 10 ^-30 esu.

Preferred NLO compounds include urea and enone derivatives, nitroaniline derivatives, various heterocyclic compounds, stilbene derivatives and merocyanines. Examples of urea and enone derivatives include:

[0022]

[Chemical 2]

And the like. Specific examples of the nitroaniline derivative include:

[0024]

[Chemical 3]

And the like. Specific examples of the heterocyclic compound include

[0026]

[Chemical 4]

And the like. Then, as specific examples of the stilbene derivative and merocyanine,

[0028]

[Chemical 5]

Examples include the following:

The compounds exemplified in Chemical formulas 2 to 5 are examples of NLO compounds usable in the present invention. Generally, compounds having a conjugated π electron system and highly polarized are large.
It is known to have the following molecular susceptibility. Therefore, even with compounds not exemplified here, the secondary molecular susceptibility is 1
Compounds larger than × 10 ^-30 esu are all N of the present invention.
It can be used as an LO compound.

The nonlinear optical material of the present invention is 10% by weight or more and less than 50% by weight, preferably 20% by weight to 50% by weight.
Less than 25% to 45% by weight of the polypeptide, and a mixture of compounds having a non-linear optical response, the composition of which is more than 50% by weight of the polypeptide.
The amount of the NLO compound is less than 50% by weight, preferably more than 50% and less than 80% by weight, and more preferably 55 to 75% by weight.

When the content of the NLO compound is 50% by weight or less, the hygroscopicity is large, so that it tends to be deteriorated with time. When the content is extremely small, the second modulated wave of the incident light is changed. The conversion efficiency of is too small to be practical. On the other hand, when the content of the NLO compound is more than 90% by weight, the amount of the guest compound with respect to the host polymer is too large, so that sufficient orientation cannot be obtained to exhibit a practical nonlinear optical response. In the present invention, other compounds may be added as long as they do not adversely affect the optical material of the present invention.

Next, an example of the method for producing the nonlinear optical material of the present invention will be given. First, the polypeptide and N
In order to mix the LO compound uniformly, the non-linear optical material of the present invention can be obtained by dissolving and mixing the polymer and the compound using both common solvents and then evaporating the solvent. Further, the non-linear optical material of the present invention is a sheet,
When used as a film or thin film optical element,
For example, a mixture of a polypeptide and an NLO compound is heated to a temperature equal to or higher than the melting point of both to be melted and sufficiently kneaded to homogenize the mixture, followed by press molding or extrusion molding to form a film, sheet or thin film. It is also possible to adopt a method of forming into a shape.

When the polypeptide to be used exhibits lyotropic cholesteric liquid crystallinity, a solution containing the polypeptide and the NLO compound is sufficiently aged for 1 to 10 days, and then the solvent is gradually evaporated to cholesteric cholesteric liquid crystal. By fixing the liquid crystal structure and simultaneously orienting the NLO compound, a nonlinear optical material having high SHG activity can be obtained. In addition, a polypeptide exhibiting thermotropic cholesteric liquid crystallinity is used to develop a more complete asymmetric alignment structure, which is then immobilized, resulting in a higher S
It is also possible to obtain a nonlinear optical material that exhibits HG activity.

As described above, only the orientational force possessed by the host polymer is used, without the aid of an external force such as an electric field.
It is one of the major characteristics of the present invention that an O compound can be asymmetrically oriented to produce a nonlinear optical material having a large nonlinear optical constant. Of course, by utilizing the force of the electric field, it is possible to realize a sufficiently asymmetrically oriented structure as described above. For example, a composition comprising a polypeptide and an NLO compound is sandwiched between two transparent electrodes and heated, and an electric field is applied while being maintained at a temperature equal to or higher than the melting point or the liquid crystal transition point, whereby the polymer and NLO compound are applied. It is also possible to obtain a non-linear optical material having an asymmetrically oriented structure fixed by cooling the compound after asymmetrically orienting it.

The non-linear optical material of the present invention, whether produced without applying an electric field or produced by applying an electric field, has an extremely stable SHG activity without deterioration over time, and has an excellent temperature and humidity. It is also stable against changes in environmental conditions such as oxygen in the air. Such SHG
The stability of activity is a great practical advantage.

As is clear from the above description,
The nonlinear optical material of the present invention has a large nonlinear optical constant, high SHG activity, and its performance does not deteriorate with time due to changes in environmental conditions. Therefore, the nonlinear optical material of the present invention can be widely used for wavelength conversion of laser light, optical modulation, optical switching, or various optical electronics such as an optical computer.

[0038]

EXAMPLES The non-linear optical material of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 A mixture of 40 wt% of poly (γ-methyl L-glutamate) having a polymerization degree of 1,050 synthesized by the NCA method and 60 wt% of p-nitroaniline was dissolved in 1,2-dichloroethane to obtain a uniform solution. .. Next, the solvent was gradually evaporated from this solution to prepare a cast film having a thickness of 1 mm, which was dried at room temperature for 1 day to obtain a SHG measurement sample. Nd ^{3+ in} this sample
/ YAG laser light (λ = 1.06 μm) was emitted,
The generation of SHG of 0.53 μm was observed, and the intensity thereof was 148 times the SHG intensity of urea used as a standard substance.

Example 2 A mixture of 30 wt% of poly (γ-dodecyl L-glutamate) having a degree of polymerization of 340 synthesized by the NCA method and 70 wt% of p-nitroaniline was melted by heating and extruded into a sheet having a thickness of 1 mm. It was used as an SHG measurement sample. Nd ³⁺ / Y for this sample
When irradiated with AG laser light (λ = 1.06 μm), λ =
Generation of SHG of 0.53 μm was observed, and the intensity thereof was 39 times that of urea used as a standard substance.

Examples 3 to 6 SHG measurement samples were prepared in the same manner as in Example 1 except that the various glutamic acid ester polypeptides and NLO compounds shown in Table 1 were used, and Nd ³⁺ / YAG laser light was prepared for each sample. The intensity of SHG generated upon irradiation with (λ = 1.06 μm) was examined. The results are shown in Table 1.

[0042]

[Table 1]

Comparative Example 1 A cast film having a thickness of 1 mm was prepared by gradually evaporating the solvent from a benzene solution containing 80 wt% of polymethylmethacrylate and 20 wt% of p-nitroaniline. This film was vacuum dried overnight at room temperature to prepare a sample for SHG measurement. Nd ³⁺ / YAG laser light (λ =
1.06 μm), but SHG did not occur at all.

Comparative Example 2 80 wt% of polyethylene oxide having a molecular weight of 20,000, p-
A sample for SHG measurement was prepared in the same manner as in Comparative Example 1 from a benzene solution containing 20 wt% of nitroaniline. Nd ³⁺ / YAG laser light (λ = 1.
(6 μm), the standard substance of urea 2.1
Only twice as weak SHG was observed.

Examples 7 to 11 Various aspartic acid ester-based polypeptides synthesized by the NCA method were used, except that NLO compounds were used.
A sample was prepared in the same manner as in Example 1, and the intensity of SHG generated when irradiated with Nd ³⁺ / YAG laser light (1.06 μm) was examined. The results are shown in Table 1.

[0046]

INDUSTRIAL APPLICABILITY The nonlinear optical material of the present invention has a large nonlinear susceptibility, exhibits a high SHG activity, and has extremely stable performance. Utilizing these excellent properties, the nonlinear optical material of the present invention can be suitably used for various devices in the field of optoelectronics such as wavelength conversion of laser light, optical modulation, optical switching, and optical computers.

Claims (1)

Claim: What is claimed is: 1. A nonlinear optical material comprising a mixture of a polypeptide and a compound exhibiting a nonlinear optical response, wherein the polypeptide exhibits cholesteric liquid crystallinity,
The second-order nonlinear molecular susceptibility of the compound exhibiting a nonlinear optical response is 10 ^-30 esu or more, and the mixture contains 10% by weight.
50% by weight or more and less than 50% by weight of the polypeptide
And a compound exhibiting a non-linear optical response of more than 90% by weight.