JPH02181734A - Manufacture of organic nonlinear optical material - Google Patents

Abstract

PURPOSE:To obtain a nonlinear optical material high in nonlinear optical effect made of an aromatic compound by applying an electric field to a host material low in viscosity and molecular weight and a nonlinear low molecular weight guest material dispersed in the host material and polymerizing them. CONSTITUTION:The optical material high in nonlinear effect can be obtained by mixing the nonlinear low-molecular-weight compound as the guest material, such as cyclic ester compound, and the polymerizable compound made of an aromatic compound having nonlocalized pi-electrons capable of being polymerized into a polymer as the host material, and a photopolymerization initiator, applying an electric field to this mixture to a orient the nonlinear compound, and polymerizing the mixture in the oriented state into a solid, thus permitting the nonlinear guest material to be well dispersed into the host material, while it is low in viscosity and molecular weight, so easily oriented by the applied electric field, and optical material having high nonlinearity effect to be obtained by polymerizing it in this state.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for producing an organic nonlinear optical material, the purpose of this invention 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 an aromatic low-molecular compound having a second-order molecular nonlinear susceptibility, and the polymerizable mixture is polymerized with the aromatic low-molecular compound oriented, thereby creating an organic nonlinear optical material. Configure the manufacturing method.

[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.
bOa), potassium dihydrogen phosphate (K)lzPOl (abbreviation KDP)], ammonium dihydrogen phosphate (NH, 11
Inorganic nonlinear optical materials such as □PO4 (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 output laser such as a laser, high conversion efficiency can be achieved. However, when using a low output 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-value αE + βE2 + γE3+... (1) However, α is the first-order molecular nonlinear susceptibility, β is the second-order, T is the third-order, E is the electric field strength, and β is the second harmonic, which is the frequency multiplication function. This is a coefficient that governs wave generation and the electro-optical effect (Pockels effect), and T is a coefficient that governs the optical force effect.

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

(For example, G. R. Meredith et al., “Non1i
near Properties of Organi
c and Polymeric Materials
” ACSSymposfua+ 5eries #2
33. American Chemical 5oci
ety, 1983) There are also materials that exhibit nonlinear optical effects in a crystalline state.

Examples include 2-methy/L/-4-nitroalinine, tonitroaniline, 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, S. Chemla et al., “Non1ine
ar 0ptical Properties of
Organic Molecules and Cry
“stals”.

Academic Press, INC; 1987.
p405-436) Materials that require a high electric field at -1 are considered to 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/mm is required to obtain a nonlinear effect of the same degree as that of a 2-methyl-4-nitroaniline crystal. It is impossible to realize this because it would cause destruction.

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 a cyclic ester, a photopolymerization initiator, and an aromatic low-molecular compound having second-order molecular nonlinear susceptibility. This can be realized by using a method for producing an organic nonlinear optical material in which a mixture is polymerized.

[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 polymerize and solidify the nonlinear low molecules in an oriented state.

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;
By polymerizing in this state, an optical material exhibiting a high nonlinear effect can be obtained.

Here, the nonlinear low molecules (guest materials) include 2-methyl-4-nitroaniline and p-nitroaniline.

Tonitroaniline, 4-dimethylamino-3'-nitrostilbene, methyl-(2,4-dinitrophenyl)-
Aminopropanate and the like are used.

In addition, examples of the cyclic esters which are polymerizable compounds (host materials) include β-butyrolactone 1 ε-captolactone,
Lactone compounds such as β-propiolactone can be used.

Figure 1 shows β-propiolactone and ε as cyclic esters.
- A reaction formula explaining the ring-opening polymerization of the kings of captolactone and δ-valerolactone.

Next, Lewis acids, cationic catalysts, anionic catalysts, etc. are used as photopolymerization initiators, but the results of experiments showed that organozinc compounds and organoaluminum compounds were effective.

Here, the mixing ratio of the nonlinear low molecule (guest material) to the polymerizable compound (host material) is preferably 0.5 to 50% by weight, preferably 1 to 20% by weight.

The mixing ratio of the photopolymerization initiator is 0.01 to 10% by weight, preferably 0.5% by weight based on the polymerizable compound (host material).
~5% by weight.

〔Example〕

30 g of dehydrated ε-caprolactone (host material), 6 g of dried p-nitroaniline (guest material), and 2 ml of a 25% toluene solution of dibutylzinc (polymerization initiator) were mixed by stirring in a box purged with nitrogen (l). A composition was obtained.

Next, add this to N! It was filled into the apparatus shown in FIG. 2 in a water box.

Here, the device shown in FIG. 2 has a glass substrate (50 x 60 mm) equipped with a transparent electrode 232'.1. A Mylar film with a thickness of 10 gm is used as a spacer 3, and the transparent electrodes 2.2' are placed on the inside to face each other, and the transparent electrodes 2.2' are connected to a power source 5 to apply an electric field to the mixed composition 4. This is what I did.

Then, a voltage of 300 V was applied to the transparent electrodes 2 and 2', and then heated to 70°C and left for 48 hours.

As a result, a yellow film was formed.

When this film was peeled off from the glass substrate 1.1', crushed, and irradiated with 1064 rv light from a Nd:YAG laser, green light emission with a wavelength of about 500 nm was observed, which doubled the frequency. I was able to confirm that.

Note that the intensity of this green light was 30 times higher than that of urea powder, which was similarly measured as a comparison.

〔Effect of the invention〕

By implementing the present invention, an optical material that exhibits a second harmonic generation function and an excellent electro-optic effect using an aromatic compound with nonlinearity, and has excellent mechanical strength, thermal stability, and stability over time can be put into practical use. can be converted into

[Brief explanation of the drawing]

FIG. 1 is a reaction formula explaining the ring-opening polymerization of various cyclic esters, 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 1! It is the source.

Claims (1)

[Claims] An electric field is applied to a polymerizable mixture consisting of a cyclic ester, a photopolymerization initiator, and an aromatic low-molecular compound having second-order molecular nonlinear susceptibility, and the polymerizable mixture is oriented in a state in which the aromatic low-molecular compound is oriented. A method for producing an organic nonlinear optical material, which comprises polymerizing it.