JPH05188416A - Organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To provide the org. nonlinear optical material which can form a crystal having SHG activity without having an object 2 center, has excellent transparency and has an absorption end wavelength in a short wavelength region by using a specific benzene deriv. as the optical material. CONSTITUTION:The 3, 5-di-t-butyl-4-hydroxybenzaldehyde expressed by formula I or the 3, 5-di-t-butyl-4-hydroxybenzoic acid expressed by formula II can form the single crystal which has no absorption at all in a visible region and has excellent thermal stability and the high SHG activity. Both are excellent in workability and high in the tolerance of phase matching conditions and are, therefore, utilizable advantageously for nonlinear optical devices, such as wavelength conversion elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic nonlinear optical material, and more particularly to an organic nonlinear optical material used in a wide range of fields such as optical computers, optical communications and optical information recording.

[0002]

2. Description of the Related Art The linear optical response of a substance indicates that the electric polarization induced in the substance is proportional to the photoelectric field due to a strong electric field obtained by laser light. Proportionality to the cube or the like is called a non-linear optical response, and a non-linear optical material refers to a material having a non-linear optical effect in which various effects generated from this non-linear optical response are summarized. This nonlinear optical material is used to amplify scattered light,
Generation means of coherent light such as oscillation and wavelength conversion, waveform,
It can be applied to control of light characteristics such as spectrum, beam space characteristics, polarization and modulation characteristics. In addition, relatively new applications include optical information processing elements such as optical space using a non-linear optical material, temporal distortion-free transmission medium, memory, and switch.

Wavelength conversion of laser light (second harmonic generation: SHG) is one of the applicable fields using materials having a nonlinear optical effect. According to this phenomenon, it is possible to easily take out coherent light having a frequency twice that of the fundamental wave laser light and having the same properties as the fundamental wave laser light, and it is possible to widely use for information recording, image processing, laser measurement and the like. Its application can be expected in the field.

As a conventional nonlinear optical material, LiNb is used.
O ₃ (LN), KTiOPO ₄ (KTP), KH ₂ PO
Inorganic crystals such as ₄ (KDP) and NH ₄ H ₂ PO ₄ (ADP) have been used, but single crystals with high optical purity are extremely expensive, and some have deliquescent properties, which makes them inconvenient to handle. There was a problem that the optical damage intensity was poor, and the second-order nonlinear susceptibility was not high. On the other hand, recently, there is an increasing expectation for an organic optical material having a faster response than an inorganic material, a high optical damage strength, and a second-order nonlinear optical performance index that is an order of magnitude larger.

[0005]

The optical non-linearity (supramolecular polarizability β) at the molecular level of organic materials can be estimated from the molecular orbital calculation, but the value of the supramolecular polarizability β at the molecular level is obtained. , Even if it is a large organic material, becomes SHG-inactive at the crystal level if the crystal has a symmetric center when crystallized. Therefore, whether or not the organic material exhibits high SHG activity cannot be judged only by the value of the supramolecular polarizability β, and it is a problem to actually synthesize the organic material, crystallize it, and evaluate it.

Although organic crystals of urea and aniline compounds have been announced as nonlinear optical materials, none of these organic compounds have sufficiently satisfactory nonlinear and linear optical characteristics. Even in MNA (2-methyl-4-nitroaniline) having an optical constant, its light absorption edge is colored because it is on the long wavelength side (visible light region), and when used as an actual wavelength conversion element, SHG Since the transmittance of light (especially blue light) is low, there is a drawback that the wavelength range is extremely limited.

Further, in the practical application of an organic material as a nonlinear optical material, in addition to the problem of the transmitted light region described above, it is desired that the organic material be stable at room temperature and form a single crystal as large as possible. However, in general, an organic nonlinear optical material is inferior in thermal stability due to a low melting point, has low dimensional accuracy, and has a problem that it is difficult to process a crystal such as cutting and polishing, or to obtain a large single crystal. there were.

Further, if the melting point is low, the change in the refractive index at room temperature is large, so that there is a problem that the temperature tolerance of the phase matching condition is small. The present invention has been made in view of the above problems, and is stable at room temperature and SHG.
An object of the present invention is to provide an organic non-linear optical material which is active and can form a crystal having no center of symmetry, is excellent in transparency, and has an absorption edge wavelength in a short wavelength region.

[0009]

According to the present invention, the structural formula (I) or (II)

[0010]

[Chemical 3]

[0011]

[Chemical 4] An organic nonlinear optical material comprising a benzene derivative represented by

The inventors of the present invention used a semi-empirical molecular orbital method, the PPP (Pariza-Pearl Pople) method, to obtain supramolecular polarizability β when various donors were introduced into benzaldehyde. The maximum absorption wavelength λ _max was calculated. Moreover, as a result of examining the influence of a bulky substituent (t-butyl group) having no symmetry center on the crystal structure and its donor property, 3,5-di-t-butyl-4-hydroxybenzaldehyde and 3,5-di-t-butyl-4-hydroxybenzaldehyde It has been found that 5-di-t-butyl-4-hydroxybenzoic acid has no absorption in the visible region and forms a single crystal having excellent thermal stability and a large SHG activity.

These compounds in the present invention can be easily synthesized by known methods. For example, 3,5-di-t-butyl-4-hydroxybenzaldehyde is 2,
By oxidizing 6-di-t-butyl-4-methylphenol, also 3,5-di-t-butyl-4-hydroxybenzoic acid can be obtained from "Organic Syntheses", Col. Vol.
IV, p.919, John Wiley & Sons, New York (1963), can be used to synthesize 3,5-di-t-butyl-4-hydroxybenzaldehyde by oxidation.

The compound of the present invention is a crude product obtained by a known method,
For example, it can be used as a nonlinear optical material by being purified by a recrystallization method, a sublimation method, or the like.

[0015]

EXAMPLES The present invention will be described in more detail by way of examples. Example 1 First, 20 g of 2,6-di-t-butyl-4-methylphenol was dissolved in 200 cc of glacial acetic acid, and 50 c of pure water was further added.
c and bromine 10 cc with stirring to this solution
Was added dropwise over 2 hours. After stirring for 1 hour, the solution was diluted with 125 cc of ice water and cooled at 0 ° C. for 3 hours to obtain crystals. This was filtered, washed with acetic acid and water, and then recrystallized from hexane to give 3,5-di-t-butyl-4-.
Hydroxybenzaldehyde was obtained. The yield was 68%.

3,5-di-t-obtained according to this example
The spectrum of butyl-4-hydroxybenzaldehyde in the visible ultraviolet region is shown in FIG. The maximum absorption wavelength is 278
nm (in 1,4-dioxane). As is clear from FIG. 1, it is shown that the semiconductor laser has a sufficiently high translucency in the wavelength region of 415 nm which is the SHG light of 830 nm,
Furthermore, it is shown that even if an inductive light source with a short wavelength is used, it has sufficient translucency.

The melting point of 3,5-di-t-butyl-4-hydroxybenzaldehyde was determined by DSC to be 18
It was 8 ° C. This is a typical SHG material, MA.
The melting point of P (methyl- (2,4-dinitrophenyl) -aminopropanoate), which is extremely higher than 69 ° C., is superior in processability to conventional SHG materials,
It has the advantage that the phase matching condition has a large tolerance.

Next, the obtained 3,5-di-t-butyl-
The SHG of 4-hydroxybenzaldehyde was evaluated by the powder method. A sample granulated to a diameter of around 100 μm is sandwiched between slide glasses, and this sample is irradiated with an Nd-YAG laser (wavelength = 1.064 μm), then
Green light with a wavelength of 2 (532 nm) was observed, and the second harmonic generated from the sample was detected by Photomul. Similarly, granular urea was used as the standard sample, and the second harmonic intensity of urea was set to 1, and relative comparison was performed. As a result, 5 of urea
It was found to show double the SHG activity.

Furthermore, 3,5-di-t-butyl-4-hydroxybenzaldehyde has good crystallinity and is stable at room temperature. Example 2 From the reaction of 3,5-di-t-butyl-4-hydroxybenzaldehyde obtained in Example 1 with silver oxide, 3,5-
Di-t-butyl-4-hydroxybenzoic acid was obtained. The yield was 72%.

3,5-di-t-obtained according to this example
The spectrum of butyl-4-hydroxybenzoic acid in the visible ultraviolet region is shown in FIG. Maximum absorption wavelength is 258 nm
(In 1,4-dioxane). As is clear from FIG. 2, the semiconductor laser 830 nm SHG light 41
It shows that the light-transmitting property is sufficiently high in the wavelength region of 5 nm, and further that the light-transmitting property is sufficient even when an inductive light source with a short wavelength is used.

The melting point of 3,5-di-t-butyl-4-hydroxybenzoic acid was 208 ° C. as measured by DSC. This is extremely higher than the melting point of MAP, which is a typical SHG material, which is 69 ° C., so that it is superior to conventional SHG materials in workability and has a large tolerance for phase matching conditions. is there. Then obtained 3,5
Evaluation of SHG of -di-t-butyl-4-hydroxybenzoic acid was performed in the same manner as in Example 1. As a result, when this sample was irradiated with an Nd-YAG laser (wavelength = 1.064 μm), green light with a wavelength (532 nm) that was half the incident light was observed, and it was found that SHG activity that is three times that of urea is exhibited. It was

Furthermore, 3,5-di-t-butyl-4-hydroxybenzoic acid has good crystallinity and is stable at room temperature.

[0023]

According to the present invention, 3,5-di-t-butyl-
4-hydroxybenzaldehyde and 3,5-di-t-
The compound selected from butyl-4-hydroxybenzoic acid is stable at room temperature and has good crystallinity, and SHG
It is an organic nonlinear optical material having a relatively large activity, excellent transparency, and an absorption short wavelength in a relatively short wavelength region. Therefore, it can be used for various nonlinear optical devices such as a wavelength conversion element and is an important material for practical use.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between wavelength and absorbance of 3,5-di-t-butyl-4-hydroxybenzaldehyde according to the present invention.

FIG. 2 is a graph showing the relationship between wavelength and absorbance of 3,5-di-t-butyl-4-hydroxybenzoic acid according to the present invention.

Claims (1)

[Claims] 1. A structural formula (I) or (II): [Chemical 2] An organic nonlinear optical material consisting of a benzene derivative represented by.