JP2698853B2 - Material for organic nonlinear optical element and organic nonlinear optical thin film using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a material for an organic nonlinear optical element and an organic nonlinear optical thin film produced using the same.

(Prior art and problems) In the field of optoelectronics, secondary organic nonlinear optical materials have been actively developed. Among these materials, for example, compounds having central symmetry in bulk crystalline state, such as long-chain nitroazobenzene, do not exhibit second-order optical nonlinearity (Second Harmonic Generation, SHG), but are symmetrical depending on the orientation. To show nonlinearity by breaking the structure (Literature example: OAAktsipetrov, N.
N. Akhmediev, EDMishina, VR Novak, JETP Lett., 37, 20
7-209 (1983)).

It is also known that the higher the degree of molecular orientation, the higher the SHG intensity. That is, not only the expression of nonlinearity can be expected by using an oriented thin film, but also a higher SHG intensity can be obtained. In the oriented thin film, the scattering of transmitted light due to the irregularity of molecules can be reduced, so that there is also a feature that light loss when a nonlinear optical waveguide is formed can be reduced. For this reason, development of a material capable of forming a highly oriented thin film has become an important issue for realizing a practical nonlinear optical material. Conventionally, in order to obtain a material excellent in both optical nonlinearity and alignment, the optical nonlinearity of a liquid crystal material already known to have excellent alignment has been studied. Table 1 shows main examples of the liquid crystal materials which have been reported so far and exhibit nonlinearity. These liquid crystal compounds exhibited only a small non-linearity as shown in Table 1 even when they were oriented by applying an electric field in the liquid crystal cell, and were not ready for practical device fabrication.

(Means for Solving the Problems) The present inventors conducted a search for a nonlinear optical material exhibiting liquid crystallinity in order to find a device material having both excellent optical non-linearity and orientation. Reached.

The present invention relates to a compound of the formula (I) (Wherein, R ₁ and R ₂ are an alkyl group or an alkyl group containing fluorine, X is hydrogen, halogen, hydroxyl, cyano, nitro, amino, dimethylamino, or R ₃ CONH group (R ₃
Is an alkyl group) and j is a compound represented by 0 or 1) alone or as a mixture with another compound, and a material for an organic nonlinear optical element, and an organic nonlinear optical thin film produced using the same. It is.

As the material for a nonlinear optical element having liquid crystallinity represented by the general formula of the present invention, for example, the following compounds can be shown as specific examples.

(Action) 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), the compound is formed on a polyimide rubbing substrate or the like conventionally used for a liquid crystal cell. It is easy to prepare an alignment thin film, and it is also easy to align an electric field using the dielectric anisotropy and spontaneous polarization of a compound. Further, the compound of the formula (I) shows a much higher SHG relative intensity than the 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 having excellent orientation can be easily obtained.

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

As a method for producing a thin film in the present invention, for example, the first method
As shown in the figure, 2 through a spacer (polyimide film) 4
The compound represented by the general formula (I) is sealed in the liquid crystal injection portion 5 between the substrates 1, and post-treatment such as application of an electric field from the electric field application terminal 3 to the electrode 2 is performed as necessary. There are a conventional method of manufacturing a liquid crystal cell having a thin film, and a method of depositing a compound represented by the general formula (I) on a substrate by vacuum evaporation. The substrate used in this case, for example, the substrate was rubbed with a glass surface in a predetermined direction, ITO, substrate was rubbed the surface of the glass in a predetermined direction with a transparent electrode such as SnO _2, polyimide, polymer film such as polyvinyl alcohol such as a substrate in combination coated substrate where the surface of the glass is rubbed in a predetermined direction, SiO, glass substrate, etc. SiO ₂ was obliquely deposited, KBr, NaCl, monocrystalline such as sapphire, and these can be used.

4 Hereinafter, the present invention will be described in more detail with reference to Examples.

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

The compounds shown in Table 3 have a higher relative strength of SHG than the conventionally studied liquid crystal materials, indicating that they are useful as materials for organic nonlinear optical elements.

(Example 2) A transparent electrode surface of a glass substrate with an ITO transparent electrode was rubbed, and two glass substrates were opposed to each other via a 10 μm spacer.
A liquid crystal cell having the structure shown in FIG. Table 4 shows the results of measuring the second-order nonlinear optical constant and the degree of polarization by injecting the compound E in Table 3 into this. Here, when measuring the second-order nonlinear optical constant, a YAG laser having a wavelength of 1.06 μm was used as a light source, and a previous report (NM Shtykov, MIBarnik, LA Beresnev, LM
Blinov, Mol. Cryst. Liq. Cryst., 124, 379-390 (1985))
The measurement was performed in the same manner as described above. In addition, the degree of deflection P (degr
Measurement of ee of polarization) is transmitted light intensity using a measurable polarization microscope, photometric values I _‖ at the brightest becomes diagonal position the polarizing orthoscopic viewing, and darkest extinction photometric value at ( It was calculated according to equation (1) using _I⊥ (45 ° rotation from the diagonal position).

P = (I _‖ -I _⊥) / (I _|| + I _⊥) (1) much larger than the fourth All compounds in Table nonlinear optical constant of the conventional study examples, and also excellent in orientation You can see that there is. Similar results were obtained when other compounds in Table 3 were used.

Example 3 2-Methyl-4-nitroaniline whose optical non-linearity measured by the powder method is 22 times that of urea, and 2-methyl-4-nitroaniline which is 115 times that of urea
Acetylamino-4-nitrodimethylaniline and compound F were mixed at a polymerization ratio of 5:95, and the nonlinear optical constant and the degree of deflection 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 a large optical nonlinearity.

Example 4 The transparent electrode surface of an ITO glass substrate with a transparent electrode was rubbed to obtain a substrate for vacuum deposition. Table 6 shows the results of measuring the second-order nonlinear optical constant and the degree of polarization by vapor-depositing the compounds F, G, and J in Table 3 on the rubbed surface by a vacuum vapor deposition method.

It can be seen that compounds E, G, and J can be formed into a thin film by a vacuum evaporation method, and a thin film having a large nonlinear optical constant can be obtained. Similar results were obtained when other compounds in Table 3 were used.

(Effects of the Invention) As described above, according to the present invention, it is possible to provide a nonlinear optical material excellent in both nonlinearity and orientation and a nonlinear optical thin film excellent in orientation, so that it is suitable for optoelectronics. Can be used for

[Brief description of the drawings]

FIG. 1 is a view showing the structure of a liquid crystal cell used in the present invention. 1 ... Glass substrate, 2 ... Electrode for applying electric field, 3 ... Terminal for applying electric field, 4 ... Polyimide film whose surface was rubbed, 5 ... Liquid crystal injection part.

Claims (2)

(57) [Claims] 1. A material for an organic nonlinear optical element, wherein a compound represented by the following general formula is used alone or as a mixture with another compound. (Wherein, R ₁ and R ₂ are an alkyl group or an alkyl group containing fluorine, X is hydrogen, halogen, hydroxyl, cyano, nitro, amino, dimethylamino, or R ₃ CONH group (R ₃
Is an alkyl group), j is 0 or 1) 2. An organic nonlinear optical thin film manufactured using a material for an organic nonlinear optical element represented by the following general formula. (Wherein, R ₁ and R ₂ are an alkyl group or an alkyl group containing fluorine, X is hydrogen, halogen, hydroxyl, cyano, nitro, amino, dimethylamino, or R ₃ CONH group (R ₃
Is an alkyl group), j is 0 or 1)