JPH04277724A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To improve the light transmittability in a short wavelength region and to exhibit a high quadratic nonlinear optical effect by consisting the above material of a specific compd. CONSTITUTION:An optical fiber type optical wavelength conversion element has the structure formed by coating a core 1 consisting of an org. nonlinear optical material with a clad 2 consisting of a material, such as glass, which does not exhibit the nonlinear optical effect. The compd. expressed by formula I exhibits the high quadratic nonlinear optical effect by using a technique of predicting the max. light absorption wavelength and quadratic molecular ultra polarization rate beta by using a PPP (pariser-parr-pole)-MO method which is a kind of molecular orbit methods. This compd. is usable adequately particularly as the org. nonlinear optical material for a second harmonic generating element. In the formula I, X denotes an electron-withdrawing group.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a novel organic nonlinear optical material used in the manufacture of various elements that utilize nonlinear optical effects, and more particularly, to a second harmonic material that utilizes the nonlinear optical effect. The present invention relates to nonlinear optical materials suitable for use in generation elements, light modulation elements, optical bistable elements, etc., and in particular, elements whose constituent elements are arrays or aggregates of films or layers.

0002

[Prior Art and Problems to be Solved by the Invention] A nonlinear optical effect is a phenomenon in which the polarization P induced by an electric field applied inside a crystal has terms of quadratic or higher order, as shown in equation (i) below. This is an optical effect that occurs along with the nonlinearity caused by P=X(1) E+X(2) E・E+X(3) E・
E・E+... These include second harmonic generation, optical rectification, optical mixing, parametric amplification, and Pockels effect.
Third-order nonlinear optical phenomena include third harmonic generation, optical bistability, Kerr effect, and the like.

In particular, 2, which occurs in proportion to the square of the electric field of light,
The following nonlinear optical effects can be applied to nonlinear optical elements that contribute to the development of the optoelectronics field, such as second harmonic generation elements, optical wavelength conversion elements using sum frequency or difference frequency, and optical modulation elements. It is attracting a lot of attention because it can be applied. At present, the materials that make up these elements are mainly KH2PO.
Inorganic materials such as 4 are used. However, the nonlinear optical constants of these inorganic materials are small, and therefore there is a problem in that extremely high voltage or extremely strong light intensity is required to operate the device.

Among inorganic materials, lithium niobate (LiN
Although lithium niobate (bO3) has the largest nonlinear optical constant, it has the disadvantage that its refractive index partially changes when irradiated with strong laser light, and it is easily damaged by light, so it is still not practical. It has not yet been standardized. In recent years, organic materials have been developed which have essentially better nonlinear optical effects than inorganic materials, such as (a) high nonlinear polarizability, (b) resistance to damage by light, and (c) high response and response speed to electric fields. Nonlinear optical materials are attracting attention [for example, “Nonlinear Optical
Properties of Organic and
Polymeric Materials”ACS
SYMPOSIUM SERIES 233, (Am
Erican Chemical Society,
(1983), "Organic Nonlinear Optical Materials" supervised by Masao Kato and Hachiro Nakanishi (CMC, 1985), etc.].

Examples of the organic nonlinear optical materials include 3-acetylamino-4-pyrrolidine-nitrobenzene (hereinafter referred to as "PAN"), which is represented by the following formulas:
2-Methyl-4-nitroaniline (hereinafter referred to as "MNA"), and p-nitro-(2-hydroxymethyl-
Pyrrolinyl) phenylene (hereinafter referred to as "NPP").

[0006]PAN:

[0007]

[Case 2]

[0008] MNA:

[0009]

[Chemical formula 3]

[0010]NPP:

[0011]

[C4]

Second harmonic generation (SHG), which is one of the second-order nonlinear optical phenomena, is used to convert a nonlinear optical material into a second harmonic that converts the wavelength of incident light (fundamental wave) to 1/2. When used in a wave generating element, in order to efficiently extract the generated second harmonic, the above-mentioned second harmonic must be used as a nonlinear optical material.
It is necessary to use a material that has high transparency to harmonics, that is, a material that has low light absorption in the wavelength region of the second harmonic (generally the optical wavelength region on the short wavelength side).

However, organic nonlinear optical materials such as PAN, MNA, and NPP all have a problem in that the second harmonic cannot be efficiently extracted because they all have large light absorption in the short wavelength region. The above problem is related to the electronic state of each compound, so replacing the carbon atom in the benzene ring of the above compound with a nitrogen atom etc. changes the electronic state and reduces light absorption on the short wavelength side. Attempts have been made, but without satisfactory results.

[0014] Furthermore, in the organic nonlinear optical material,
Second-order nonlinear susceptibility X that controls the second-order nonlinear optical effect
(2) In order to increase the polarization at the molecular level (
It is necessary to increase the second-order molecular hyperpolarizability β in the following formula (ii), which represents molecular polarization μ. μ=αE+βE・E+γE・E・E+…
…(ii
) [However, α, β, γ... are primary, secondary, and tertiary, respectively.
The molecular hyperpolarizability of the following..., E represents the electric field vector] The above second-order molecular hyperpolarizability β is largely dependent on the magnitude of charge transfer within the molecule, and the larger the charge transfer within the molecule, the greater the charge transfer within the molecule. , the second-order molecular hyperpolarizability β also increases. However, when the intramolecular charge movement becomes large, the light wavelength absorption region of the nonlinear optical material becomes a long wavelength, and there is a problem that the transmittance of light in the short wavelength region deteriorates.

Furthermore, in order for a nonlinear optical material to exhibit a second-order nonlinear optical effect, each molecule arranged in the crystal must not cancel out the permanent dipole moment of each other. It is necessary that the arrangement of molecules in has no center of symmetry. However, it is currently almost impossible to determine the molecular arrangement from the molecular structure, and even if the molecular structures are very similar, the molecular arrangement is not necessarily the same, and the second-order molecular hyperpolarizability β is large. Even with materials, there is a problem in that many materials do not produce second-order nonlinear optical phenomena in their crystalline state because the arrangement of molecules in their crystals has a center of symmetry.

That is, the larger the hyperpolarizability of each molecule in the above formula (ii), the larger the microscopic, that is, molecular-level polarization μ, but if the arrangement of molecules in the crystal has a center of symmetry, However large the polarization μ at the molecular level is, the macroscopic polarization P at the crystal level expressed by the above formula (i) is small and may not cause a second-order nonlinear optical phenomenon.

As described above, the optical properties of organic crystalline materials are greatly affected not only by the properties of the molecules but also by the arrangement of the molecules in the crystal. In many cases, it is uniquely determined by the molecular species of the crystal, and it is extremely difficult to control the molecular arrangement in the crystal. Therefore, there is a problem in that the optical properties of the molecules themselves are affected by the molecular arrangement, and the inherent nonlinear optical effects of the molecules constituting the organic crystal material cannot be fully exhibited.

The present invention has been made in view of the above circumstances, and aims to provide an organic nonlinear optical material that has excellent light transmittance in the short wavelength region and exhibits a large second-order nonlinear optical effect. The purpose is

[0019]

[Means and effects for solving the problems] In order to solve the above problems, the present inventors have developed a method using PPP (Pariser-Parr-Pole)-M, which is a kind of molecular orbital method.
By using the method of predicting the maximum optical absorption wavelength (λmax) and the second-order molecular hyperpolarizability β using the O method and determining a molecular structure suitable for a nonlinear optical element from the results, the following general It has been discovered that the compound represented by formula (I) exhibits a high second-order nonlinear optical effect and can be particularly suitably used as an organic nonlinear optical material for second harmonic generation elements, and in completing the present invention. It's arrived.

[0020]

[C5]

[However, in the formula, X represents an electron-withdrawing group. ]
That is, the organic nonlinear optical material of the present invention is characterized by comprising a compound represented by the above general formula (I). The second-order molecular hyperpolarizability β of the compound represented by the general formula (I) is calculated by the following formula (iii) using the molecular parameters obtained by the PPP-MO method [J.
L. Oudar, J., Chem. , Phys.
, 67, 446 (1977)].

[0022]

[Math 1]

[However, e is the charge of the electron,

[0024]

[Outside 1]

is h/2π (h is Planck's constant), m is the mass of the electron, w is the energy difference between the ground state and the excited state,

[0026]

[Outside 2]

is the incident light energy, f is the oscillator strength, and Δ
μge indicates the difference in dipole moment between the ground state and the excited state] Note that it is appropriate to predict the second-order molecular hyperpolarizability β of a specific material using the above PPP-MO method and equation (iii). There have been reports proving this [Hiroshi Shimizu et al., Proceedings of the Autumn Annual Meeting of the Chemical Society of Japan (19
87)]. According to the above report, when the second-order molecular hyperpolarizability β was calculated using the above method for various conventionally known nonlinear optical materials for which the measured value of the second-order molecular hyperpolarizability β was known, the calculated value It has been confirmed that there is good agreement between the measured values and the measured values. Therefore, the above method can calculate the second-order molecular hyperpolarizability β of a new compound as an organic nonlinear optical material.
It can be said that this is a reasonable method for predicting.

Among the compounds represented by the above general formula (I), the most suitable compound for the present invention is a compound in which the electron-withdrawing group X is a cyano group and is substituted at the 4-position of the benzene ring.
Examples include compounds represented by the following formula (II).

[0029]

[C6]

The compound represented by the above formula (II) is PP
The second-order molecular hyperpolarizability β calculated by the P-MO method and equation (iii) is 17×10-30 of MNA described above.
140×10-30 es, which is extremely high compared to esu
reach u. Furthermore, the above compound has a maximum light absorption wavelength (λmax) of 359n determined from the light absorption spectrum.
m, and has extremely excellent light transmittance in the short wavelength region.

In the compound represented by the above general formula (I), the electron-withdrawing group X includes, in addition to the above-mentioned cyano group,
For example, substitution of acyl groups such as formyl, acetyl, propionyl, butyryl, pentanoyl, hexanoyl, octanoyl, benzoyl, etc.; carbamoyl, methylcarbamoyl, dimethylcarbamoyl, ethylcarbamoyl, propylcarbamoyl, hexylcarbamoyl, laurylcarbamoyl, benzylcarbamoyl, phenylcarbamoyl, etc. Carbamoyl group which may have a group; amino, methylamino, dimethylamino, ethylamino,
Amino groups that may have an alkyl group such as diethylamino, propylamino, butylamino, hexylamino, and octylamino; Aralkylamino or arylamino groups such as benzylamino, benzhydryl, tritylamino, phenylamino, and diphenylamino; carboxy Group; alkoxycarbonyl group such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl, aryloxy which may have a substituent such as phenoxylcarbonyl, p-nitrophenyloxycarbonyl, etc. Esterified carboxy groups such as aralkyloxycarbonyl such as carbonyl, benzyloxycarbonyl, benzhydryloxycarbonyl; methanesulfonyl, ethanesulfonyl, propanesulfonyl, butanesulfonyl, trifluoromethanesulfonyl, 2,2,2-trifluoroethane Alkanesulfonyl groups which may have a halogen atom such as sulfonyl; acylamino groups such as formamide, acetamide, propionamide, butyrylamino, hexanoylamino, benzoylamino; nitroso group; sulfo group; methoxysulfonyl, ethoxysulfonyl, propoxysulfonyl , alkoxysulfonyl such as butoxysulfonyl, pentyloxysulfonyl, hexyloxysulfonyl, octyloxysulfonyl, phenoxysulfonyl, esterified sulfonyl such as phenoxysulfonyl which may have a substituent such as p-cyanophenoxysulfonyl; Examples include a sulfamoyl group which may have a substituent such as sulfamoyl, methylsulfamoyl, ethylsulfamoyl, phenylsulfamoyl, and benzylsulfamoyl; a sulfino group; and a thiocarboxy group.

The substitution position of the electron-withdrawing group X is as described above in 4.
It is not limited to the position, and can be substituted at any appropriate position on the benzene ring. The organic nonlinear optical material of the present invention, which is composed of the above-described compound, can be incorporated in a host lattice such as a polymer, a clathrate compound (clathrate compound), a solid solution, or a liquid crystal.
It can be used in various forms, such as in a thin layer deposited on a support (Langmuir-Prodgett monolayer), as a single crystal, as a powder, as a solution.

As described above, the organic nonlinear optical material of the present invention exhibits an extremely high second-order nonlinear optical effect and is excellent in transmittance of light in the short wavelength region, so that it can be used as a second harmonic generating element, etc. It can be particularly suitably used as a nonlinear optical material for optical wavelength conversion elements, as well as other elements using nonlinear optical materials, such as phase modulation elements, phase conjugate optical elements, amplitude modulation elements, frequency modulation elements, and pulse modulation elements. ,
Optical modulation elements such as polarized wave modulation elements, optical storage elements, optical pulse waveform control elements, optical limiters, differential amplification elements, optical transistors, A/D conversion elements, optical logic elements, optical multivibrators, optical flip-flops, etc. It can also be suitably used in optical bistable devices such as optical dipole circuits.

When forming the above-mentioned various elements from the organic nonlinear optical material of the present invention, the organic nonlinear optical material itself may generally be used as the element. However, when forming an optical wavelength conversion element such as a second harmonic generation element or an optical modulation element such as a phase modulation element from the organic nonlinear optical material of the present invention, the organic nonlinear optical material is used for an optical waveguide. It is preferable to have an optical waveguide type structure [J.
Zyss, J. Molecular Electron
ics 1, 25 (1985), etc.].

In the above case, since the light can be confined within the optical waveguide, the optical power density can be increased, and the interaction length can be lengthened, making it possible to improve the efficiency of wavelength conversion, phase modulation, etc. In addition, phase matching using mode dispersion is also possible. Figure 1 shows an example of a device using the organic nonlinear optical material of the present invention in an optical waveguide.
~ Shown in Figure 4.

FIG. 1 shows a schematic diagram of an optical fiber type optical wavelength conversion element as an example of an optical waveguide type wavelength conversion element. The above-mentioned optical fiber-type optical wavelength conversion element uses a core (optical waveguide) 1 made of the organic nonlinear optical material of the present invention (hereinafter referred to as "nonlinear medium") in a medium that does not exhibit a nonlinear optical effect (hereinafter referred to as "isotropic medium") such as glass. It has a structure covered with a cladding 2 consisting of a medium (referred to as "medium").

In the optical fiber type optical wavelength conversion element, when light such as a laser beam focused by a lens or the like is incident on the core 1 from one end surface, the nonlinear medium forming the core 1 produces a second-order nonlinear optical effect. Therefore, in core 1, 1/2 of the incident fundamental wave (indicated by the dashed line in the figure)
A second harmonic of wavelength (indicated by a two-dot chain line in the figure) is generated and emitted from the other end surface of the core 1 along with the fundamental wave. Note that in order to extract only the second harmonic from the light emitted from the other end surface of the core 1, it is sufficient to separate the two using a spectroscopic means such as a prism or a filter.

FIGS. 2 and 3 are schematic diagrams showing other examples of optical wavelength conversion elements, and in the drawings, a dashed line and a dashed double dot line represent the fundamental wave (dashed line) as in FIG. 1, respectively. and the second harmonic (double-dashed line). The optical wavelength conversion element in FIG. 2 has a substrate 22 made of an isotropic medium, and
A layered optical waveguide 21 made of a nonlinear medium is formed, and the optical wavelength conversion element shown in FIG. A layered optical waveguide 31 made of a nonlinear medium is formed.

The optical wavelength conversion element having the above structure can be used in the same manner as the optical wavelength conversion element shown in FIG. FIG. 4 shows a schematic diagram of a horizontally operated optical waveguide type optical modulation element as a phase modulation element. The above-mentioned optical waveguide type optical modulation element includes an optical waveguide 41 made of a nonlinear medium provided in a substrate 42 made of an isotropic medium, and a substrate 42 made of an isotropic medium.
It is constructed by arranging two electrodes 43, 43 along the longitudinal direction of the optical waveguide 41 at symmetrical positions on the surface of the optical waveguide 41.

In the optical waveguide type optical modulator, when a voltage is applied between the electrodes 43, 43, both the electrodes 43, 43
An electric field is formed between them, and the refractive index of the nonlinear medium forming the optical waveguide 41 changes accordingly. When light incident from one end of the optical waveguide 41 in the length direction passes through the optical waveguide 41 and is emitted from the other end surface, if the refractive index of the nonlinear medium changes, the phase of the emitted light changes. Therefore, by changing the voltage applied between the electrodes 43, the phase of the emitted light can be modulated.

In the optical wavelength conversion element shown in FIGS. 1 to 4 above, in order to form the core 1 and the optical waveguides 21, 31, 41, for example, the raw material of the nonlinear medium is converted into a capillary made of an isotropic medium, respectively. Among them, a method in which crystals are precipitated by heating and melting on an optical waveguide substrate made of an isotropic medium or between optical waveguide substrates made of an isotropic medium, and then cooling slowly, a vacuum evaporation method on the substrate, A method of precipitating crystals using a high frequency sputtering method or the like is employed.

Further, crystals are precipitated in the capillary, on the substrate, or between the substrates from a solution of the raw materials dissolved in a suitable organic solvent to form the core 1 and the optical waveguide 21,
31, 41 can also be formed. Furthermore, in some cases, after treating the portion that should become the contact interface between the nonlinear medium and the isotropic medium, such as the inner wall surface of the capillary or the surface of the substrate, with an alignment treatment agent, the nonlinear medium is precipitated as described above. , crystal growth may be performed.

The above-mentioned alignment treatment agents include inorganic salts and organic salts (for example, hexadecyltrimethylammonium bromide, etc.), thin films made of suitable polymers (for example, polyamide, etc.), metal complexes, metal thin films (for example, diagonal Examples include vapor-deposited gold thin films, etc. Note that the nonlinear optical element using the organic nonlinear optical material of the present invention in the optical waveguide is not limited to the above example. It may be a modulation element, or it may be a form in which a voltage is directly applied to the nonlinear medium itself, such as a crystal. Note that in optical modulators, the direction of electric field application for efficient phase modulation varies depending on the symmetry of the nonlinear medium, the direction of the crystal axis, etc., so it is recommended to change the electrode configuration appropriately based on these factors. good.

[0044]

EXAMPLES The present invention will be explained in more detail below based on examples. Example 4 - 10 g (0.085 mol) of aminobenzonitrile was added to 22.1 ml of concentrated hydrochloric acid cooled to 0°C, and the liquid temperature was reduced to 0.
A solution was obtained by stirring and dissolving the mixture while maintaining the temperature at °C.

Next, 55% of sodium nitrite was added to the above solution.
．． A solution prepared by dissolving 8 g (0.085 mol) in 13 ml of distilled water was gradually added dropwise, followed by stirring and mixing. Next, 53.3 g (0.423 mol) of sodium sulfite was added to the above solution.
A solution prepared by dissolving 126.9 ml of distilled water was added thereto, and the mixture was stirred under ice-cooling. Thereafter, the solution was returned to room temperature and stirred for 10 minutes, then heated to 60-70°C and stirred for 2 hours.

After adding 90 ml of concentrated hydrochloric acid to the above solution, heating was stopped and the solution was allowed to stand overnight to cool naturally. The crystals of 4-cyanophenylhydrazine hydrochloride precipitated by the above cooling were filtered, washed, and purified. Next, the above 4
-cyanophenylhydrazine hydrochloride 4.1 g (0.02
4 mol), benzalacetophenone 5.0 g (0.0
24 mol) and 2.0 g (0.024 mol) of sodium acetate were added to 100 ml of acetic acid, heated to 100° C., and stirred and mixed overnight.

After distilling off acetic acid from the reaction solution, the resulting solid was treated with activated carbon, and the treated reaction product was purified by recrystallization using ethyl acetate to obtain pale yellow crystals. Obtained. Regarding the obtained crystals, the compound was identified by melting point measurement, nuclear magnetic resonance (NMR), and infrared spectroscopy.
-(4-cyanophenyl)-3,5-diphenyl-1,
2-pyrazoline (melting point 157-158°C, hereinafter referred to as "CPD")
It was confirmed that it was P.

[0048]

[C7]

Evaluation Test 1 Regarding the CPDP obtained in the above example, S. K. Kurt
z, T. T. Perry, J. Apply. Phy
s. , 39, 3798 (1968), the intensity of the generated second harmonic was measured by the following measurement method. -Measurement method The CPDP crystal powder obtained in the above example was packed in a glass cell, and the glass cell was heated with a Nd:YAG laser (wavelength 1.
064μm) and is included in the light emitted from the cell.
The SHG intensity of the second harmonic at a wavelength of 532 nm was measured using a photomultiplier tube.

[0050] As a result, it was confirmed that CPDP generated a second harmonic with an intensity three times that of urea powder, which was a standard substance. Evaluation test 2 CPDP obtained in the above example and NPP, which is a conventional material,
Dissolve MNA and PAN in ethanol,
Prepare an ethanol solution with a concentration of 4 x 10-4 mol/l,
A spectral transmission curve in a wavelength range of 250 to 500 nm was measured. The results are shown in Figure 5.

From the results shown in FIG. 5 above, CPDP, which is a compound of the present invention, has a light absorption wavelength region that is shorter than conventional substances such as NPP, MNA, and PAN, and does not absorb light of 420 nm or more. understood.

[0052]

[Effects of the Invention] As detailed above, the organic nonlinear optical material of the present invention has excellent light transmittance in the short wavelength region,
In addition, since it exhibits a large second-order nonlinear optical effect, it can be particularly suitably used as a second-order nonlinear optical material for various nonlinear optical elements.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an optical waveguide type wavelength conversion element as a nonlinear optical element using the organic nonlinear optical material of the present invention.

FIG. 2 is a schematic diagram showing another example of the optical waveguide type wavelength conversion element.

FIG. 3 is a schematic diagram showing still another example of the optical waveguide type wavelength conversion element.

FIG. 4 is a schematic diagram showing an example of an optical waveguide type optical modulation element as a nonlinear optical element using the organic nonlinear optical material of the present invention.

FIG. 5 is a graph showing spectral transmission curves of CPDP as a compound of the present invention and conventional substances NPP, MNA, and PAN.

[Explanation of symbols]

1 Core (optical waveguide) 21 Optical waveguide 31 Optical waveguide 41 Optical waveguide

Claims (2)

[Claims] 1. An organic nonlinear optical material comprising a compound represented by the following general formula (I). embedded image [However, in the formula, X represents an electron-withdrawing group. ] [Claim 2]
The organic nonlinear optical material according to claim 1, wherein X in the general formula (I) is a cyano group, and is substituted at the 4-position of the benzene ring.