JPH02181733A - Manufacture of organic nonlinear optical material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for producing an organic nonlinear optical material, the purpose of this is to put into practical use a method for producing a polymeric material with high second-order molecular nonlinear susceptibility. An electric field is applied to a polymerizable mixture consisting of a polymerization initiator and an aromatic low-molecular compound having second-order molecular nonlinear susceptibility, and light is irradiated with the aromatic low-molecular compound oriented to polymerize the polymerizable mixture. This constitutes a method for manufacturing an organic nonlinear optical material.

[Industrial application field]

The present invention relates to a method for producing a polymeric material with high second-order molecular nonlinear susceptibility.

With the practical application of optical communications, there is a demand for higher functionality of optical devices.

That is, by using a second-order nonlinear optical effect, it is possible to realize an optical switch, wavelength conversion, etc., and by using a third-order nonlinear optical effect, functions such as a phototransistor can be realized.

Conventionally, lithium niobate (LiN) has been used as a nonlinear optical material.
bO*), potassium dihydrogen phosphate (KtLzPOg (abbreviation KDP)), ammonium dihydrogen phosphate (NH4H2P
Inorganic nonlinear optical materials such as O4 (APD)] were used.

However, these materials do not have sufficient nonlinearity, and for example, when it comes to wavelength conversion, which is a frequency multiplication function, YAG
(yttrium-aluminum-garnet) When using a high-power laser such as a laser, high conversion efficiency can be achieved. However, when using a low-power laser such as a semiconductor laser, high conversion efficiency cannot be obtained.

However, since semiconductor lasers are frequently used in optical communications, an optical device that has a high nonlinear effect is required even when using a low-power laser.

[Conventional technology]

The polarizability P of an optical material can be expressed by the following formula.

P=αE+βE2+γE3+... (1) However, α is the first-order component, child nonlinear susceptibility, β is the second-order component, T is the third-order component, E is the electric field strength, knee, and β is the frequency multiplication function. This is a coefficient that governs the generation of harmonics and the electro-optic effect (Pockels effect), and γ is a coefficient that governs the optical power effect.

Now, in order for an optical material to exhibit a large β value, it is necessary for the molecule to have a non-centrosymmetric structure, and aromatic compounds with delocalized π electrons in organic materials are different from conventional inorganic materials. It is known to exhibit a relatively high nonlinear optical effect.

(For example, G. R. Meredith et al., “Non1i
near Properties of Organi
c and Polymeric Materials
” ACSSymposium+ 5eries 1I
233. American Chemical 5oc
iety, 1983, etc.) There are also materials that exhibit nonlinear optical effects in a crystalline state.

Examples include 2-methyl-4-nitroaniline, 1m-nitroaniline, and 4-dimethylamine-3'-nitrostilbene.

That is, it has an electron-donating group and an electron-accepting group with a benzene nucleus in between, thereby exhibiting high polarizability.

However, organic crystals have the problem that it is difficult to obtain high-quality crystals, and the crystals themselves are soft and difficult to process.

In addition, as a general tendency, when low-molecular-weight compounds with high polarizability crystallize, their molecules are arranged so that their polarities cancel each other out, and as a result, the crystal as a whole loses its polarity and takes on a centrosymmetric structure. There are many.

For these reasons, it is not practical to use crystals as organic nonlinear optical materials.

Therefore, a nonlinear low-molecular material is dispersed in a host material (polymer) to form a film, and an electric field is applied to this to create a non-centrosymmetric guest-host structure. Attempts are being made to achieve this.

(For example, Ri, S., ChemLa et al., 'Non1nea
r 0ptical Properties of O
rganic Molecules and Crys
tals”.

Acade+eic Press, INC; 1987
．． p405-436) It is generally believed that materials that require a high electric field have high nonlinearity stability at room temperature.

However, in experimental examples where polymethyl methacrylate or the like is used as a polymer material (host material) and p-nitroaniline is used as a nonlinear low molecule (guest material), even with electric field orientation, a high nonlinear effect is achieved as expected. It is difficult.

For example, when comparing this with a 2-methyl-4-nitroaniline crystal, which has a non-centrosymmetric structure from the beginning, an electric field of about IMV/m is required to obtain a nonlinear effect of the same degree. It is impossible to achieve this.

For these reasons, it has been necessary to put organic nonlinear optical materials into practical use that can achieve high nonlinear effects.

[Problem to be solved by the invention]

It is known that aromatic compounds with delocalized π-electrons exhibit higher nonlinear optical effects than conventional inorganic materials, but it is difficult to commercialize nonlinear optical materials using such aromatic compounds. is the issue.

[Means to solve the problem]

The above problem was solved by applying an electric field to a polymerizable mixture consisting of an acrylic or methacrylic compound, a photopolymerization initiator, and an aromatic low-molecular compound having second-order molecular nonlinear susceptibility, and aligning the aromatic low-molecular compound. This can be realized by a method for producing an organic nonlinear optical material in which a polymerizable mixture is polymerized by irradiating light.

[Effect]

The present invention consists of a low-molecular compound (guest material) consisting of an aromatic group having delocalized π electrons and having nonlinearity, a polymerizable compound (host material) that can be polymerized to become a polymer, and a photopolymerization initiator. An electric field is applied to this mixed composition to orient the nonlinear low molecules, and light is irradiated to polymerize and solidify this mixed composition.

In other words, since the electric field is applied while the nonlinear, low-molecular guest material is dispersed in a state where the host material is in a low-viscosity, low-molecular state and easily moves, orientation is easy;
Since light irradiation is carried out in this state to cause polymerization, an optical material exhibiting a high nonlinear effect can be obtained.

The nonlinear low molecule (guest material) is 2, methyl-4-nitroaniline, 2p-nitroaniline.

Tocotroaniline. 4-dimethylamino-3-nitrostilbene, methyl-(2,4-dinitrophenyl)-aminopropanate, etc. are used.

In addition, examples of polymerizable compounds (host materials) include acrylic acid, methyl acrylate, and methacrylic acid.

Acrylics such as methyl methacrylate and ethyl methacrylate. Compounds of methacrylic acid can be used.

Since these materials are nonpolar compounds, they have little interaction with nonlinear low molecules (guest materials), and therefore can be oriented with a weak electric field.

Figure 1 shows a reaction formula explaining the polymerization of an acrylic compound.
Examples of photopolymerization initiators include sulfur compounds such as thiophenol and 2-mercaptobenzazole, carbonyl compounds such as benzophenone and Michler's ketone, peroxides such as benzoyl peroxide and 1-butyl peroxide, and azobisisobutyronitrile. Azobis compounds are effective.

Further, as a light source for polymerization, ultraviolet light or visible light from a mercury lamp, a xenon lamp, a fluorescent lamp, a xenon mercury lamp, etc. can be used.

Next, the mixing ratio of the nonlinear low molecule (guest material) to the polymerizable compound (host material) is 1 to 100% by weight, preferably 5 to 50% by weight.

The mixing ratio of the photopolymerization initiator is 0.5 to 20% by weight, preferably 1 to 10% by weight based on the polymerizable compound (host material).
Weight%.

〔Example〕

Example 1; 100 ml of methyl methacrylate in a 300 mff1 flask
g and Abbisisobutyronitrile 0.5g, 80
The mixture was heated to a temperature of 100.degree. C., stirred for 30 minutes, and then rapidly cooled to obtain uncured methyl methacrylate.

To this, 2-methyl-4-nitroaniline (guest material R)
5 g and 2 g of t-butyl peroxide (polymerization initiator) were mixed under yellow lighting to make a mixed composition, which was then added to the second
It was filled into the apparatus shown in the figure.

In the device shown in FIG. 2, glass substrates 1 and 1' with transparent electrodes 2 and 2' are placed facing each other with a Mylar film having a thickness of 10 μm as a spacer 3, with the transparent electrodes 2 and 2' inside. , the transparent type i2, 2' is connected to the power source 5, and the mixed composition 4 is
This allows an electric field to be applied to the

Then, while applying a voltage of 100μ to the transparent electrode 2.2', a mercury lamp (manufactured by Ushio Inc., USH-250BY) was used.
) for 20 minutes, a yellow film with low internal scattering was formed.

When this film was peeled off from the glass substrates 1 and 1', crushed, and irradiated with 11064n light from an Nd HYAG laser, green light emission with a wavelength of about 500 nm was observed, which allowed for doubling the frequency. I was able to confirm it.

Note that the intensity of this green light was approximately 10 times as strong as that of urea powder, which was similarly measured as a comparison.

Example 2: UV-curable modified acrylic adhesive (trade name, ThreeBond 3021)...Logp
- Nitroaniline (guest material)...mix in 2 g,
A mixed composition was prepared by stirring.

This mixed composition was filled in the apparatus shown in FIG. 2 in the same manner as in Example 1, and irradiated with a mercury lamp for 20 minutes while applying a voltage of 100 V between the transparent electrodes 2 and 2'.

As a result, we were able to create a transparent film with a yellowish tint.

When this film was peeled off from the glass substrate 1.1', crushed, and irradiated with 11064n light from a Nd:YAG laser, green light emission with a wavelength of approximately 500 nm was observed, resulting in double frequency doubling. I was able to confirm that.

Note that the intensity of this green light was approximately four times as strong as that of urea powder, which was similarly measured as a comparison.

Become.

[Brief explanation of the drawing]

FIG. 1 is a reaction formula explaining the polymerization of an acrylic compound, and FIG. 2 is a cross-sectional view of the apparatus used in the examples. In the figure, 1.1' is a glass substrate, 2.2' is a transparent electrode, 4 is a mixed composition, and 5 is a power source. 〔Effect of the invention〕

Claims (1)

[Claims] An electric field is applied to a polymerizable mixture consisting of an acrylic or methacrylic compound, a photopolymerization initiator, and an aromatic low-molecular compound having second-order molecular nonlinear susceptibility, and the aromatic low-molecular compound is oriented and irradiated with light. and polymerizing the polymerizable mixture.