JPH02183232A - Material for organic nonlinear optical element and organic nonlinear optical thin-film formed by using this material - Google Patents

Abstract

PURPOSE:To obtain the material for the nonlinear optical element which is excellent in both nonlinearity and orientability by using a specific compd. alone or in combination with other compds. CONSTITUTION:The compd. expressed by the formula I is used alone or in combination with the other compds. In the formula I, R1, R2 denote an alkyl group or alkyl group contg. fluorine, X denotes hydrogen, halogen, hydroxyl group, cyano group, nitro group, amino group, dimethyl amino group, etc.,; j denotes 0 or 1. The material for the nonlinear optical device which is excellent in both the optical nonlinearity and orientability is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a material for organic nonlinear optical elements and an organic nonlinear optical thin film produced using the same.

(In the formula, R1 and R2 are an alkyl group or a fluorine-containing alkyl group, and X is hydrogen, halogen, hydroxyl group, cyano group, nitro group, amino group, dimethylamino group, or R3C0
NH group (R3 is an alkyl group), j is Omanah 1) (2)
An organic nonlinear optical thin film produced using a material for an organic nonlinear optical element represented by the following general formula.

(Prior Art and Problems) In the field of optoelectronics, second-order organic nonlinear optical materials are being actively developed.

Among these materials, compounds that have central symmetry in the bulk crystalline state, such as long-chain nitroazobenzene, exhibit second-order optical nonlinearity (Second Harmoni).
c Generation, SHG), but by breaking the symmetrical structure due to orientation, it begins to show nonlinearity (Literature example: O, A, Aktsipe
trov, N.N., Akhmediev, E.D.
Mishina, V.R., Novak, JETP L
ett, 37, 207-209 (1983)).

It is also known that the higher the order of molecular orientation, the higher the SHG intensity. That is, by forming an oriented thin film, not only can the expression of nonlinearity be expected, but also it is possible to obtain a larger SHO strength. In the oriented thin film, scattering of transmitted light due to molecular irregularities can be reduced, so optical loss when used as a nonlinear optical waveguide can be reduced. For this reason, the development of materials that can form highly oriented thin films has become an important issue in order to realize practical nonlinear optical materials. Conventionally, in order to obtain materials that are excellent in both optical nonlinearity and orientation, the optical nonlinearity of liquid crystal materials, which are known to have excellent orientation, has been investigated. Table 1 shows the main examples of liquid crystal materials exhibiting nonlinearity that have been reported so far. These liquid crystal compounds are:
Even when an electric field was applied to align the liquid crystal in a liquid crystal cell, it exhibited only small nonlinearity as shown in Table 1, and could not be used for producing practical devices.

(Means for Solving the Problems) In order to find a material for an element that is excellent in both optical nonlinearity and orientation, the present inventors conducted a search for nonlinear optical materials exhibiting liquid crystallinity, and as a result, the present invention was developed. reached.

(In the formula, R1 and R2 are alkyl groups or fluorine-containing alkyl groups, X is hydrogen, halogen, hydroxyl group, cyano group, nitro group, amino group, dimethylamino group, and R3C0
Materials for organic nonlinear optical elements characterized by using a compound represented by NH group (R3 is an alkyl group), j is 0 or 1, alone or in combination with other compounds, and materials prepared using the same It is an organic nonlinear optical thin film.

Specific examples of the material for nonlinear optical elements that exhibit liquid crystallinity and are not represented by the general formula of the present invention include the following compounds.

Table 1, LIq,shir)lsl,,1ノ41jIsojsoυ(
l so5b) (n-1-12, m-1-12) (n-1-12, m-1-12) υ (n-1-12, m-1-12) (n=1-11 . m-1-12) υ (n=1-12. m-f-12) U (n-1-12, m-1-12) N (n-1, 12, m-1-12) ( n=1-12. m-1-12) (n=1-12. m-th 2) (n=1-12. m-th 2) (n=1-12. m-1-12) ( Effect) Since the compound represented by the formula (I) of the present invention has a liquid crystal temperature range specific to each molecule (specific example: Table 2), it can be oriented on a polyimide rubbed substrate, etc. that has been conventionally used in liquid crystal cells. It is easy to produce a thin film, and it is also easy to align with an electric field using the dielectric anisotropy and spontaneous polarization of the compound. Furthermore, the compound of formula (I) exhibits a much higher relative SHG intensity than conventionally studied liquid crystal compounds. That is, by forming the material for a nonlinear optical element having liquid crystal properties of the present invention into a thin film by a method such as vapor deposition or injection between two substrates, a nonlinear optical thin film with excellent orientation can be easily obtained.

Although the compound used in combination with the compound of the present invention does not necessarily have to exhibit nonlinearity, further improvement in nonlinearity can be expected by mixing a compound exhibiting large nonlinearity. Generally, it is difficult to obtain an oriented thin film with a compound exhibiting large nonlinearity, but by mixing it with the compound of the present invention, the orientation can be improved. Compounds mixed for this purpose include, for example, 2-methyl-4
Nitroaniline, nitroaniline derivatives such as 2-acetylamino-4-nitrodimethylaniline, urea derivatives such as N,N'-dimethylurea, methyl-(2,4-dinitrophenyl)-aminopropanate, leucine-p-
Examples include amino acid derivatives such as nitroanilide, stilbene derivatives such as 4-dimethylamino-4-stilbene, heterocyclic compounds such as merocyanine, and molecular salts thereof.

As a method for producing a thin film in the present invention, for example, as shown in FIG. If necessary, post-processing such as applying an electric field through the electrode 2 from the electric field application terminal 3 to form an oriented thin film can be performed using conventional liquid crystal cell manufacturing methods, or by vacuum evaporation on the substrate with the general formula (I). There are methods of depositing compounds shown in ). The substrate used in this case may be, for example, a substrate whose glass surface is rubbed in a certain direction, an ITOSnO
A substrate whose surface is made of glass with a transparent electrode rubbed in a certain direction, a substrate whose surface is rubbed in a certain direction from a glass coated with a polymer film such as polyimide or polyvinyl alcohol, a glass substrate whose surface is obliquely evaporated with 5iO1SiO, etc., KBr. Single crystals such as , NaCl, sapphire, and substrates combining these can be used.

(Margin below) Table 2 Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example 1) The relative intensities of the second-order nonlinear optical constants measured by the powder method for typical compounds represented by formula (I) are shown in Table 3 as reference materials for nonlinear optical constant measurements. Urea was used as the light source, and a YAG laser with a wavelength of 1.06 μm was used as the light source. The measurement temperature is room temperature. Table 3 also shows the measurement results for the five materials shown in Table 1.

It can be seen that the compounds shown in Table 3 have larger SHG relative strengths than conventionally studied liquid crystal materials, and are useful as materials for organic nonlinear optical elements.

(Example 2) ■The transparent electrode surface of the obtained glass substrate with transparent electrode was rubbed, and the first
A liquid crystal cell with the structure shown in the figure was fabricated. Table 4 shows the results of injecting Compound E in Table 3 and measuring the second-order nonlinear optical constants and degree of polarization. It was used as a light source and was previously reported (N, M, 5htykov, M, 1.
Barnik, L.A., Beresnev, L.M.
.

B11nov, Mo1. Cryst, Liq, Cry
The measurements were carried out in the same manner as in J. St., 124.379-390 (1985)). Moreover, the degree of deflection P(degr
ee of polarization) is measured using a polarizing microscope that can measure transmitted light intensity, and the photometric value I at the diagonal value that is the brightest in polarized orthoscope observation.

and the photometric value at the darkest extinction value (45 from the diagonal value)
° rotation)■ was calculated using equation (1).

P=(I −I)/(I 1) (1)■
It can be seen that all the compounds in Table 4 of 91 above have significantly larger nonlinear optical constants than those of the conventionally studied examples, and also have excellent orientation. Note that similar results were obtained when other compounds shown in Table 3 were used.

(Example 3) 2-Methyl-4-nitroaniline, whose optical nonlinearity measured by the powder method is 22 times that of urea, and 2-methyl-4-nitroaniline, whose optical nonlinearity is 115 times that of urea.
-Acetylamino-4-nitrodimethyaniline and Compound F were mixed at a weight ratio of 5:95, and the nonlinear optical constants and degree of polarization were measured in the same manner as in Example 2. The results are shown in Table 5.

It is clear that the optical nonlinearity was further improved by mixing with a compound having large optical nonlinearity.

(Example 4) (1) The transparent electrode surface of the glass substrate with a transparent electrode of 0 was rubbed to obtain a substrate for vacuum deposition. Compounds F, G, and T shown in Table 3 were deposited on the rubbed surface using a vacuum evaporation method, and the second-order nonlinear optical constants and degree of polarization were measured. Table 6 shows the results.

It can be seen that compounds E, G, and J can be formed into thin films by vacuum evaporation, and thin films having large nonlinear optical constants can be obtained. Similar results were obtained using other compounds in Table 3.

Table 3 Table 3 (Continued) Measurement temperature 15°C Table 6 (Effects of the invention) As explained above, according to the present invention, a nonlinear optical material excellent in both nonlinearity and orientation and a nonlinear optical material excellent in orientation are obtained. Since a nonlinear optical thin film can be provided, it can be suitably used for optoelectronics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the structure of a liquid crystal cell used in the present invention. l... Glass substrate, 2... Electrode for applying electric field, 3
... Terminal for applying electric field, 4 ... Polyimide film whose surface has been subjected to rubbing treatment, 5 ... Liquid crystal injection part.

Claims (2)

[Claims] (1) A material for an organic nonlinear optical element, characterized in that a compound represented by the following general formula is used alone or in combination with other compounds. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_1 and R_2 are alkyl groups or fluorine-containing alkyl groups, and X is hydrogen, halogen, hydroxyl group, cyano group, nitro group, amino group, dimethylamino group, or R_
3CONH group (R_3 is an alkyl group), j is 0 or 1
) (2) An organic nonlinear optical thin film produced using a material for an organic nonlinear optical element represented by the following general formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_1 and R_2 are alkyl groups or fluorine-containing alkyl groups, and X is hydrogen, halogen, hydroxyl group, cyano group, nitro group, amino group, dimethylamino group, or R_
3CONH group (R_3 is an alkyl group), j is 0 or 1
)