JPH05281586A - Nonlinear optical material - Google Patents

Abstract

PURPOSE:To provide an organic nonlinear optical material of excellent transparency in a visible area and crystallinity without large reverse symmetric center in the secondary nonlinear optical effect by forming this nonlinear optical material of a specific urea derivative. CONSTITUTION:This nonlinear optical material is formed of an N-alkyl-N'-(4- nitrophenyl) urea derivative expressed by a formula. In the formula, R represents an alkyl group of a deuterium-substituted alkyl group. As the alkyl group, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, n-butyl group, a sec-butyl group, an iso-butyl group or a tert-butyl group functions effectively. This N-alkyl-N'-(4-nitrophenyl) urea derivative can be obtained by reacting nitrophenyl isocyanate, for instance, and alkylamine or an aqueous solution equivalent to R with acid or a base as a catalyst. The symmetric property is thereby lowered, and the nonlinear optical material can be converted into active material to secondary nonlinear optical effect in a wide wavelength area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic non-linear optical material having a crystal having good transparency in the visible region and having no inversion symmetry center which exhibits a large second-order non-linear optical effect.

[0002]

2. Description of the Related Art The non-linear optical effect is a phenomenon in which, when very strong light passes through an object, the electric field of the light polarizes a substance, which causes optical harmonics due to the induced polarization and the incident light itself changes. Say. Although such a phenomenon has been known before the invention of the laser, much has come to the fore with the advent of laser light. In particular, the development of lasers is largely responsible for the elucidation of phenomena such as optical harmonic generation, optical parametric oscillation / amplification, optical phase conjugation, and optical bistability, which have recently attracted attention for application to optical functional devices.

The above-mentioned non-linear optical effect can be applied to conversion of infrared light into visible light or ultraviolet light, optical amplification, optical switch, optical modulation, and distortion-free transmission of optical signals. Devices that show effects are positioned as key functional materials in the fields of optical information processing and optical communications, where demand is ever increasing.

Conventionally, as a substance showing a non-linear optical effect,
For example, potassium dihydrogen phosphate (KDP), lithium niobate
Inorganic compounds such as (LiNbO ₃ ) and β-barium borate (BBO) have been the subject of research, and some of them have already been put to practical use as device materials. However, the substance exhibiting the nonlinear optical effect is not limited to the inorganic dielectric compound, and is also found in the organic compound. Moreover, the nonlinear optical action of organic compounds is caused by the movement of π electrons that are delocalized in the molecule, so that the induced polarization is higher than that of σ electrons of an inorganic dielectric, which is strongly bound to the nucleus and restricted by lattice vibration. Very fast and big. In fact, it has been elucidated that 2-methyl-4-nitroaniline (MNA) shows a figure of merit that is 2000 times or more that of lithium niobate [BFLEVINE et al, J. Ap.
ply.Phys., 50, 2523 (1979)].

From the above, among the nonlinear optical effects, the second-order nonlinear optical effects, which are expected to be applied as optical functional elements at the earliest, are expected to be practically applied. , MNA (Japanese Patent Laid-Open No. 55-500960), nitropyridine-
1-oxide derivative (JP-A-56-92870, JP-A-56-92870)
-94333) has been proposed as an organic nonlinear optical material.

[0006]

In the organic compound,
It is well known that it is effective to introduce an electron-donating group and an electron-withdrawing group into the molecule to increase the dipole moment of the molecule in order to enhance the second-order nonlinear optical effect. There is. However, there remain important unsolved issues in this regard. That is, in order to develop the second-order nonlinear optical effect, the crystal must be in a form without the center of inversion symmetry.

However, organic compounds having a large dipole moment in the molecule are arranged so as to cancel each other's dipole moments when crystallized, and as a result, the molecule has a large second-order supramolecular polarizability β. However, due to the center of inversion symmetry as a crystal or molecular assembly, it may not exhibit a quadratic nonlinear effect. Further, since a large intramolecular charge transfer occurs, electronic transition absorption exists in the near-ultraviolet to visible region, which leads to a loss of transparency, which is important as an optical material. Actually, there are many organic compounds having such properties.

Therefore, in developing an organic compound-based material which mainly focuses on the second-order nonlinear optical effect, the molecule has a large supramolecular polarizability β without impairing the transparency, and is of a good quality with no inversion symmetry center. It is an important subject to synthesize a compound that allows crystals to be easily obtained.

The inventors of the present invention have earnestly studied the relationship between the secondary supramolecular polarizability β and the transparency and the modification of the symmetry in an aromatic compound having an electron-withdrawing group and an electron-donating group. As a result, certain N-alkyl-N '-(4-
Nitrophenyl) urea derivatives have a large second-order supramolecular polarizability β, have no inversion center of symmetry when forming crystals or molecular aggregates, and can significantly improve transparency in the near-UV to visible region. The present invention has been developed by elucidating the facts such as the above.

Therefore, an object of the present invention is to provide an organic nonlinear optical material having excellent transparency in the visible region and having crystallinity without a center of inversion symmetry having a large second-order nonlinear optical effect.

[0011]

A non-linear optical material according to the present invention for achieving the above object comprises an N-alkyl-N '-(4-nitrophenyl) urea derivative represented by the following chemical formula. Is a structural feature.

In the above formula, R represents an alkyl group or an alkyl group substituted with deuterium. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, sec-butyl group, iso-
A butyl group or a tert-butyl group functions effectively.

The N-alkyl-N '-(4-
The nitrophenyl) urea derivative is Nd: YA in powder form.
Irradiation with G laser (λ = 1064 nm) produces a remarkably strong second harmonic of green. Especially in the single crystal state, there are some that generate a second harmonic wave with an intensity exceeding that of powder. Further, the powder state is white or milky white, and the single crystal state is colorless and transparent, and the cutoff wavelength is significantly shifted to the short wavelength side.

In the case of infrared light having a fundamental wave of 1 to 1.2 μm, the fundamental wave may be absorbed by the harmonic absorption of the stretching vibration of C—H, and converted into thermal vibration. Therefore,
When the intensity of the fundamental wave is strong, the temperature of the crystal rises and the phase matching condition may change, or the angle of the emitted light may change, but this phenomenon occurs when the hydrogen of the alkyl group with large overtone absorption is replaced by deuterium. It is possible to effectively prevent it by shifting the absorption region to the long wavelength side as the compound form.

In the above N-alkyl-N '-(4-nitrophenyl) urea derivative, for example, nitrophenyl isocyanate is converted into an acid (BF ₃ .Et ₂ O, HCl, AlCl ₃ , R ₂ Sn (OAc) ₂ Or the like) or a base (Et ₃ N, pyridine, AcONa, etc.) as a catalyst to react with an alkylamine corresponding to R or an aqueous solution thereof.

[0015]

According to the present invention, the symmetry is lowered by introducing a urea bond into an organic compound having a strong tendency to form a crystal of an inversion symmetry center due to a large dipole moment,
Provided is a novel nonlinear optical material having physical properties converted into a material which is active against a second-order nonlinear optical effect in a wide wavelength range.

Generally, since the propagation constants of the fundamental wave and the harmonics do not match in the crystal, it is difficult to generate the harmonics in the crystalline state. This matching is called phase matching. If this phase matching is not achieved, the generation of harmonics cannot be observed. However, since the crystal of the compound according to the present invention enables phase matching over a wide range, it exhibits a non-linear optical function of generating a second harmonic of high intensity.

[0017]

【Example】

Example 1 8.0 g (60 mmol) of 4-nitrophenyl isocyanate and a catalytic amount of n-butyltin dilaurate (2 mmol) were dissolved in tetrahydrofuran, 10 g of an aqueous solution of methylamine was added, and the solution was dissolved in a water bath at 50 ° C. The reaction was stirred for 4 hours. After completion of the reaction, the concentrated and precipitated reaction product was washed with hexane,
Drying at a temperature of 50 ° C. gave N-methyl-N ′-(4-nitrophenyl) urea. Obtained N-methyl-N'-
The properties of (4-nitrophenyl) urea were as follows. Melting point: 245 ± 1 ° C (DSC measurement) Molecular weight: 195 (FD-MS measurement) Analysis result [ ¹ H-NMR (solvent weight DMSO)]: δ 9.05,1H, singlet, NH, δ 8.10,2H, two Heavy line, Ar-H, δ 7.60,2H, double line, Ar-H, δ 6.20,1H, single line, NH, δ 2.45,3H, double line, CH ₃ ,

Example 2 N-Ethyl-N '-(4-nitrophenyl) urea was obtained under the same conditions as in Example 1 except that the kind of the alkylamine aqueous solution was changed. The properties of this product measured in the same manner as in Example 1 are as follows. Melting point: 160 ± 1 ℃ Molecular weight: 209 Analysis result: δ 9.00,1H, singlet, NH, δ 8.10,2H, doublet, Ar-H, δ 7.60,2H, doublet, Ar-H, δ 6.25,1H, singlet, NH, δ 3.15,2H, quintet, CH ₂ , δ 1.05,3H, triplet, CH ₃ ,

Example 3 Using the same conditions as in Example 1 except that the kind of the aqueous alkylamine solution was changed, Nn-propyl-N '-(4-
Nitrophenyl) urea was obtained. Example 1 for this
The properties measured in the same manner as above were as follows. Melting point: 152 ± 1 ° C Molecular weight: 223 Analysis result: δ 8.96,1H, singlet, NH, δ 8.10,2H, doublet, Ar-H, δ 7.60,1H, doublet, Ar-H, δ 6.25,1H, singlet, NH, δ 3.00,2H, quadruplet, CH ₂ , δ 1.45,2H, sextuple, CH ₂ , δ 0.85,3H, triplet, CH ₃ ,

Example 4 N-iso-propyl-N'- was used under the same conditions as in Example 1 except that the kind of the aqueous alkylamine solution was changed.
(4-Nitrophenyl) urea was obtained. The properties of this product measured in the same manner as in Example 1 are as follows. Melting point: 190 ± 1 ° C Molecular weight: 223 Analysis result: δ 8.85,1H, singlet, NH, δ 8.10,2H, doublet, Ar-H, δ 7.60,2H, doublet, Ar-H, δ 8.15,1H, singlet, NH, δ 3.60,1H, octet, CH, δ 1.10,6H, doublet, CH ₃ ,

Example 5 Nn-butyl-N '-(4-nitrophenyl) urea was obtained under the same conditions as in Example 1 except that the kind of the aqueous alkylamine solution was changed. The properties of this product measured in the same manner as in Example 1 are as follows. Melting point: 150 ± 1 ℃ Molecular weight: 237 Analysis result: δ 9.00,1H, singlet, NH, δ 8.10,2H, doublet, Ar-H, δ 7.60,2H, doublet, Ar-H, δ 6.25,1H, singlet, NH, δ 3.15,2H, quartet, CH _2, δ 1.45,2H, quint, CH _2, δ 1.30,2H, sextet, CH _2, δ 0.90,3H, Triple line, CH ₃ ,

Example 6 N-iso-butyl-N '-(4 was prepared by using the same conditions as in Example 1 except that the kind of the alkylamine aqueous solution was changed.
-Nitrophenyl) urea was obtained. The properties of this product measured in the same manner as in Example 1 are as follows. Melting point: 138 ± 1 ° C Molecular weight: 237 Analysis result: δ 9.00,1H, singlet, NH, δ 8.10,2H, doublet, Ar-H, δ 7.60,2H, doublet, Ar-H, δ 6.30,1H, singlet, NH, δ 3.05,2H, triplet, CH ₂ , δ 1.75,1H, ninefold, CH, δ 0.90,6H, doublet, CH ₃ ,

Example 7 Using the same conditions as in Example 1 except that the kind of the aqueous alkylamine solution was changed, N-sec-butyl-N '-(4
-Nitrophenyl) urea was obtained. The properties of this product measured in the same manner as in Example 1 are as follows. Melting point: 138 ± 1 ℃ Molecular weight: 237 Analysis result: δ 8.90,1H, singlet, NH, δ 8.10,2H, doublet, Ar-H, δ 7.60,2H, doublet, Ar-H, δ 6.15,1H, singlet, NH, δ 3.65,1H, septet, CH, δ 1.45,2H, quintet, CH ₂ , δ 1.10,3H, doublet, CH ₃ , δ 0.90,3H, triplet , CH ₃ ,

Example 8 N-tert-butyl-N'- was used under the same conditions as in Example 1 except that the kind of the aqueous alkylamine solution was changed.
(4-Nitrophenyl) urea was obtained. The properties of this product measured in the same manner as in Example 1 are as follows. Melting point: 173 ± 1 ° C Molecular weight: 237 Analysis result: δ 8.85,1H, singlet, NH, δ 8.10,2H, doublet, Ar-H, δ 7.60,2H, doublet, Ar-H, δ 6.15,1H, singlet, NH, δ 1.30,9H, singlet, CH ₃ ,

Next, a sample in which each of the nonlinear optical compounds of Examples 1 to 8 was prepared to have a particle size of 60 to 100 μm was sandwiched between glass slides, and this was subjected to Nd: YAG laser with a Q switch.
The intensity of the second harmonic (SHG) generated from the sample was measured by irradiating it with a 10 nsec pulse. For comparison, 2-methyl-4-nitroaniline (MNA) was also measured (comparative example). The results are shown in Table 1 in comparison with the type of R group and the cutoff wavelength. The SHG intensity is shown as a relative intensity ratio when urea is 1.

[0026]

[0027]

As described above, N-alkyl-N'-
The nonlinear optical material of the present invention comprising a (4-nitrophenyl) urea derivative has a very large second-order supramolecular polarizability β even though the cutoff wavelength exists in the short wavelength region, and The crystal has no center of reflection symmetry, and the molecules have a good orientation so that they can effectively utilize each other without canceling out dipole moments, and thus exhibit a high SHG intensity. Therefore, it can be expected to be applied to a wide range of applications as various optical functional elements such as wavelength conversion elements and optical control elements that utilize nonlinear optical effects.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sakuhi August Takeshi 1-2-2 Uchisaiwaicho, Chiyoda-ku, Tokyo Sumitomo Bakelite Co., Ltd. (72) Inventor Kiyozo Miyata 3-18, Shimotoya, Hoya-shi, Tokyo No.26

Claims (2)

[Claims] 1. An N-alkyl-represented by the following chemical formula:
A non-linear optical material comprising an N '-(4-nitrophenyl) urea derivative. [Chemical 1] However, in the above formula, R represents an alkyl group or a deuterium-substituted alkyl group. 2. R in the chemical formula is a methyl group, an ethyl group,
n-propyl group, iso-propyl group, n-butyl group,
sec-butyl group, iso-butyl group or tert
-The non-linear optical material according to claim 1, which is a butyl group.