KR960015086B1 - Nonlinear optical material - Google Patents

Abstract

The organic nonlinear optical material for optical devices is composed of heterocyclic compound containing nitro group as an electron acceptor functional group, which is expressed as general formula (I) and (II), where A is nitro functional group, X and Y are carbon or nitrogen atoms to which hydrogen is attached, B is hydrogen or acetyl group, Z is hydrogen atom or carbon double bonded oxygen atom. The heterocyclic compound containing nitro group comprises 5-nitrobenzene imidazole, 4-nitrobenzotriazole, 5-nitroindazole, 4-nitroindole, 5-nitroindoline, 5-nitroisetine or 1-acetyl-5-nitroindoline, etc.

Description

Organic Nonlinear Optics of Heterocyclic Compounds

1 is a schematic diagram of an apparatus for secondary nonlinearity measurement of nonlinear optics.

2a and 2b are stereoviews of the X-ray crystal structure of 5-nitroindole.

The present invention relates to an organic nonlinear optical material, and more particularly, to the use of a heterocyclic compound of the following general formula (I) or (II) having a nitro group as a functional group receiving electrons as an organic nonlinear optical material.

In the general formulas above, A is a nitro functional group; X and Y are each a carbon or nitrogen atom to which hydrogen is attached; B is hydrogen or an acetyl group; Z becomes a hydrogen or oxygen atom, and if oxygen, forms a double bond with the carbon to which it is attached.

Recently, much attention has been paid to the rapid development of optical communication using optical fibers and the development of optical connection circuits capable of processing optical signals more quickly and efficiently.

Compared to electronic circuits, this optical circuit can eliminate disturbances to external magnetic fields, and it can transmit a lot of information on a small line by using available frequency bands, and can transport and store a lot of information without changing electrical signals into optical signals. This will revolutionize data communication. In addition, parallel processing and interference-free interconnection have the advantage that they can be used as optical devices in all parts of the optical computer in the long term.

Since the nonlinear optical material interacts with the electric field of the incident light to change the properties of the incident light frequency, phase, amplitude, etc., it can be used as an optical device for rectifying, modulating and switching the optical signal.

Secondary nonlinear phenomena among nonlinear phenomena depend on the magnitude and nature of the secondary nonlinear coefficients (X ⁽²⁾ ). That is, a special case such as the second harmonic generation (SHG) effect, which converts the frequency of incident light twice, which is doubled in the field of laser, making the light in the infrared region visible. This is already used for the purpose of converting light in the visible region into light in the ultraviolet region. For example, recently developed in China, beta barium borate (BBO) and lithium triborate (LBO) crystals have been spotlighted as excellent nonlinear optical materials and are sold worldwide. However, foreign studies have shown that organic materials, compared with inorganic ones, can, theoretically, predict materials that are more likely to be in the air; Second, the nonlinear optical effect is about 10-100 times higher; Third, the damage threshold for the laser is about 100 times higher than that of the inorganic material; Fourth, response time is short; Fifth, the number of organic substances currently known has more than millions of development possibilities. Since the discovery of high nonlinear optical effects over organic materials about 10 years ago, the possibility of various organic materials as optical devices has been proved, and the development of useful organic materials as nonlinear optical materials is very active worldwide.

The present inventors have studied various organic compounds which are expected to have high efficiency as nonlinear optical materials. As a result, the heterocyclic compound of the following general formula (I) or (II) having a nitro group as an electron accepting group is used as an organic nonlinear optical material. I found it very useful.

In the general formulas above, A, X and Y, B and Z are as defined above.

Examples of compounds of the present invention useful as novel organic nonlinear optics include 5-nitrobenzeneimidazole, 6-nitrobenzeneimidazole, 5-nitroidazole, 6-nitroidazole, 7-nitroidazole, 4- Nitroindole, 6-nitroindole, 7-nitroindole, 5-nitroindolin, 6-nitroindolin, 1-acetyl-5-nitroindolin, 5-nitrocetin, 5-nitrobenzotriazole, and the like. Can be. Their chemical formula is as follows.

Some of the compounds may be obtained by purchasing commercial heteromolecular compounds and purifying them through recrystallization methods, and some compounds may be prepared by applying various conventional synthetic methods.

Hereinafter, the present invention will be described in detail through examples and tests.

Example 1

Purification of 5-nitroindole

1.5 g of 5-nitroindole was added to 30 ml of ethanol, dissolved completely while heating, and 0.25 g of charcoal was added and stirred for about 30 minutes. The solution was filtered and then treated with a gravity filter to obtain a clear yellow solution. The solvent was removed under reduced pressure, and the crystals formed by lowering ondol were filtered and dried in vacuo to obtain purified 5-nitroindole.

Example 2

Synthesis of 1-acetylindolin

8 ml of indolin was dissolved in 100 ml of acetic anhydride, refluxed for 1 hour, cooled, and 500 ml of water was added thereto. The crystals thus formed were filtered, washed with cold methanol and dried in vacuo to yield the target compound.

Melting Point: 103 ℃ (Literature Value: 102-105 ℃)

Example 3

Synthesis of 1-acetyl-5-nitroindolin

Into a mixed solution of 100 ml of concentrated nitric acid and 35 ml of sulfuric acid, 12.5 g of 1-acetylindolin was added little by little while maintaining a temperature of 10-20 ° C., followed by reflux for 12 hours. After stirring, 500 ml of cold distilled water was added, and the precipitates formed therein were collected, washed with water, filtered, and dried. Recrystallization from ethanol yielded the target compound.

Melting Point: 170-173 ℃ (Literature Value: 173-175 ℃)

Infrared spectrometer (KBr): ν 1670 (m, NO ₂ ), 1493 (m, NO ₂ ), 1301 (m, NO ₂ ).

Example 4

Synthesis of 5-nitroindolin

1.2 g of 1-acetyl-5-nitroindolin was dissolved in a mixed solution of 5 ml ethanol and 10 ml hydrochloric acid and refluxed for 30 minutes. After filtering the solid formed after reflux, the remaining solution was basified with an aqueous ammonia solution, and the solid precipitate formed at this time was filtered and then recrystallized with methanol to obtain the target compound.

Melting Point: 91-93 ℃ (Literature Value: 92-93 ℃)

[Test Example 1]

Efficiency measurement of nonlinear optical materials

In order to determine the efficiency of the heterocyclic compound having a nitro group according to the present invention as a nonlinear optical material, the nonlinearity of various compounds was measured using a device as shown in FIG. 1 and the results are shown in Table 1. It was. The X ⁽²⁾ value, called secondary bulk susceptibility, is a measure of the nonlinearity of nonlinear optical materials, which means that the larger this value can be used as an excellent nonlinear optical material. Six compounds showed efficiency, of which 5-nitroindole showed the greatest efficiency, about 20 times that of the control urea. 5-nitroindole can be used as an excellent nonlinear optical material because it has about 4 times higher efficiency than MAP and nearly similar efficiency to NMA.

K: SHG efficiency of KDP U: SHG efficiency of urea

nd: Can't check signal

[Test Example 2]

Crystal structure of 5-nitroindole

By discovering the correlation between X-ray crystal structure and efficiency, we can invent superior nonlinear optical materials with greater efficiency. The inventors have discovered the crystal structure as shown in the accompanying FIG. 2 by X-ray diffraction in order to identify the cause of 5-nitroindole having high efficiency. In order to have high efficiency, the molecular hyperpolarizability of the molecule itself, i.e., β value must be increased and the molecules must be arranged in such a way that the dipole moment in the crystal is not canceled out. The fact that 5-nitroindole had a crystal structure of Fdd2, an asymmetric space group meeting the above conditions, was investigated using X-ray diffraction. the angle between (a = 4.348 (4), b = 24,574 (3), c = 27,858 (4) Å, vol = 16Å 3, Z = 16) In the case of the compounds belonging to this space group molecular charge transfer axis and the polar axis Has been reported in the literature to have a high efficiency when the optimum condition is 54.74 ^o , which is found to be very close to the theoretical value of 54.72 ^o in the case of 5-thironiindole, which is consistent with high efficiency. The β value was calculated based on the bibliographic report of the dipole moment difference between the ground state and the excited state of 5-nitroindole and the ultraviolet visible light spectrometer. The value of 21.2 × 10 ^-30 esu was relatively high. The compounds of the present invention can be used as better nonlinear materials if they are formed into high quality pure large single crystals and their mechanical properties are enhanced.

Claims (2)

An organic nonlinear optical material useful as an optical element comprising a heterocyclic compound of the following general formula (I) or (II) having a nitro group as an electron accepting group In the general formulas above, A is a nitro functional group; X and Y are each a carbon or nitrogen atom to which hydrogen is attached; B is hydrogen or an acetyl group; Z becomes a hydrogen or oxygen atom, and if oxygen, forms a double bond with the carbon to which it is attached. The method of claim 1, wherein the bicyclic compound having a nitro group is 5-nitrobenzeneimidazole, 6-nitrobenzeneimidazole, 5-nitroindazole, 6-nitroidazole, 7-nitroidazole, 4 -Nitroindole, 5-nitroindole, 6-nitroindole, 7-nitroindole, 5-nitroindolin, 6-nitroindolin, 1-acetyl-5-nitroindolin, 5-nitrocetin, and 5-nitro Organic nonlinear optics, characterized in that it is selected from the group consisting of benzotriazoles.