JP2901764B2 - Organic nonlinear optical material and organic nonlinear optical thin film element using the material - Google Patents

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 having a large nonlinear optical effect and an organic nonlinear optical material which can be used for an optical signal processing element such as optical mixing, optical parametric oscillation, optical harmonic generation or electro-optical effect. The present invention relates to a nonlinear optical thin film element.

[0002]

2. Description of the Related Art Recently, a substance that generates light of a component other than incident light from the outside of a system has attracted attention as a so-called nonlinear optical material. This is because this kind of material has two different frequencies.
Light mixing that generates light having a frequency equal to the sum of the types of incident light, optical parametric conversion of the incident light into two types of light having different frequencies, or conversion of the incident light into second or third harmonics (SHG, respectively) , THG) plays an important role as an optical signal processing material. Further, it is considered that such a property of this kind of material will become an elemental technology of an optical computer that will be realized with the progress of optical communication technology and optoelectronic integrated circuit (OEIC) technology.

As a conventional nonlinear optical material, an inorganic material is known, and as a specific example, in a uniaxial crystal, KH ₂ PO ₄ (abbreviated as KDP) and NH ₄ H ₂ P are used.
O ₄ (abbreviated as ADP), LiNbO ₃ , Ag ₃
In the case of AsS ₃ , AgGaSe ₂ , CdGeAs ₂ , Se, Te, etc., and in a biaxial crystal, KTiPO ₄ (KTP
Is abbreviated), ferroelectric crystals such as Ba ₂ NaNb ₅ O ₁₅ have been known. However, many of these substances have drawbacks such as easy absorption of moisture and low efficiency of light mixing due to small nonlinear constant.

On the other hand, recently, an organic nonlinear optical material having a larger nonlinear constant than the above-mentioned inorganic one has attracted attention. In addition, organic substances are expected to have a faster response and a higher optical destruction threshold than inorganic substances because their nonlinearity is electronic polarization caused by intramolecular delocalized π electrons. Such organic nonlinear optical materials are described in detail in, for example, literatures (Organic Nonlinear Optical Materials, supervised by Masao Kato and Hachiro Nakanishi, CMC, 1985).

[0005]

However, as described in the above-mentioned literature, some organic nonlinear materials have a large nonlinearity in a molecular state as represented by p-nitroaniline. While having the polarizability β, it is often observed that the crystal state does not show any second-order nonlinear optical effect at all. P-Nitroaniline in the molecular state has a large nonlinear polarizability β because it has a structure in which an electron-donating group (-NH ₂ ) and an electron-withdrawing group (-NO ₂ ) are added to a π-electron conjugated ring That's why. Also, the second-order nonlinear optical effect is not exhibited in the crystal state because the crystal state has a structure having inversion symmetry, so that the polarization of each molecule cancels out and the magnitude of the macroscopic polarization becomes zero. It is.

When a non-linear optical material is applied to an optical computer or an active element for optical communication, it is essential to make the material thinner. For this reason, various attempts have been made in the past, such as growing a nonlinear optical material into a plate-like crystal, or dispersing a low-molecular nonlinear material in a polymer material, but satisfactory results have not always been obtained. Did not. The present invention has been made in view of such a point, and accordingly, an object of the present invention is to provide an organic nonlinear optical material that exhibits a nonlinear optical effect without inversion symmetry in a crystalline state. I do. Further, an object of the present invention is to provide a transparent, homogeneous and non-aggregated liquid crystal obtained by controlling the molecular orientation of an organic nonlinear optical material by a single-molecule film-forming technique by the Langmuir-Blodgett method (hereinafter referred to as LB method). It is an object of the present invention to provide an organic nonlinear optical thin film element having an excellent thin film and a large nonlinear optical effect, and useful for an optical element such as a light-light conversion element.

[0007]

According to the present invention, there is provided an organic nonlinear optical material comprising a 5-alkylamino-2-nitrobenzoic acid represented by the following formula 1, in order to solve the above problems. Further, the present invention provides a compound represented by the following formula (1):
An organic nonlinear optical thin-film element, characterized in that a thin film containing -alkylamino-2-nitrobenzoic acid is used. The LB method can be used for forming the thin film, for example.

[0008]

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[0009]

As described above, according to the present invention, the 5
Since it is an organic nonlinear optical material composed of -alkylamino-2-nitrobenzoic acid, it exhibits a nonlinear optical effect without inversion symmetry in a crystalline state. That is, a nitro group with a large electron-withdrawing property on the benzene ring, a carboxyl group with a large electron-donating property at the ortho and para positions, and a long-chain alkyl introduced to prevent inversion symmetry. It is.

[0010] The organic nonlinear optical thin film element of the present invention is a thin film containing 5-alkylamino-2-nitroaniline having a large nonlinear polarizability of molecules, and is composed of a thin film in which the molecular orientation is controlled. As is clear from the experimental results described later, a remarkable nonlinear optical effect of emitting light corresponding to the second harmonic of the light incident thereon is exhibited.

[0011]

Example 1 (1) Synthesis of Organic Nonlinear Optical Material Among the compounds represented by the above general formula, 5-stearylamino-2-nitrobenzoic acid (st-A) wherein n is 17
The method for synthesizing NBA) will be described. However, it should be understood that the names of chemicals used, numerical conditions, treatment methods, and the like described in the following synthesis examples are merely examples.

First, 4.6 g (0.025 mol) of 5-amino-2-nitrobenzoic acid and 8.3 of stearyl bromide were used.
g (0.025 mol) and sodium hydrogen carbonate 2.1 g
Is dissolved in 100 ml of hexamethylphosphoric triamide,
React at 100 ° C for 4 hours. After allowing to cool to room temperature, the reaction mixture was added to 1 liter of water, and the formed precipitate was collected by filtration, washed with water and dried. The obtained crude product was washed by suspending in hexane, and then recrystallized from ethanol.

The organic compounds synthesized as described above were identified by elemental analysis and infrared absorption spectrum, respectively. The results of the elemental analysis were as shown below. C: 69.14% H: 9.59% N: 6.22% The calculated values are C: 69.09, H: 9.74, N:
6.44%.

The infrared absorption spectrum was measured with a carbon tetrachloride solution. As shown in FIG. 1, the wave number was 2900 cm ^-1.
Methylene group near wave number 3400 cm ^-1-amino group near, carboxyl group in the vicinity of a wave number of 1740 cm ^-1, wave number 1
Aromatic ring absorption was observed at around 600 and 1520 cm ^-1 , respectively. The UV absorption spectrum of this material was measured as a chloroform solution. As shown in FIG. 2, the spectrum had a peak at 345 nm. From the above data, the organic compound produced according to this example was identified as st-ANBA represented by the following formula 2.

[0015]

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(2) Manufacture of Organic Nonlinear Optical Thin Film Element Using st-ANBA synthesized as described in (1) above, L
An example of a method for manufacturing a thin film in which a plurality of monomolecular layers are stacked by the method B will be described. The outline of the LB method is as follows. Floating a molecule having a hydrophilic group and a hydrophobic group in the same molecule on the surface of the water.
It is called "deployment." Further, the water in which the molecules are developed is hereinafter referred to as “subphase aqueous solution”. ), When an appropriate pressure is applied from the lateral direction, the hydrophilic groups of the molecules come into contact with the water surface and are regularly arranged to form a monomolecular film. When a solid substrate (eg, a glass substrate) is immersed in the monomolecular film and the substrate is lifted, the monomolecular film adheres to the glass substrate. Subsequently, when the substrate is immersed again across the same water surface where the monomolecular film is spread, further monomolecular film adheres, and when the substrate is pulled up, further monomolecular film adheres.
By repeating the immersion and lifting operations in this manner, a monomolecular cumulative film can be obtained. This method is called a vertical immersion method. Alternatively, a monomolecular cumulative film can be obtained by bringing a glass substrate close to and in contact with a plane of the monomolecular film on the water surface and repeating the contact. This method is called a horizontal deposition method.

In this example, first, a surface pressure-area curve was measured to evaluate the characteristics of the developed film. The measurement conditions were as shown below. The subphase was an aqueous solution containing cadmium chloride [CdCl ₂ ] at a molar concentration of 4 × 10 ⁻⁴ and potassium hydrogen carbonate [KHCO ₃ ] at 5 × 10 ⁻⁵ , and the water temperature was set to 15 ° C. The sample was st-ANBA
Was dissolved in chloroform, and this sample was developed in a subphase. FIG. 3 is a surface pressure-area curve showing the area (軸² / molecule) on the horizontal axis and the surface pressure (dyn / cm) on the vertical axis.

In the accumulation, a surface pressure was kept constant at 15 dyn / cm, and a cumulative film was formed on a quartz glass substrate by a vertical immersion method to produce a thin film element. The reason why the quartz glass substrate is used is to enable measurement of an absorption spectrum in an ultraviolet region, and other types of glass substrates may be used if unnecessary. Successful accumulation can be evaluated by the ratio of the area of the substrate crossing the water surface to the area of the developed film on the water surface that has decreased at that time (referred to as the accumulation ratio).

In this example, the accumulation ratio was 1, indicating that the accumulation was performed well. Furthermore, the obtained LB
The film was a transparent thin film without any aggregation. The figure shows an ultraviolet absorption spectrum of a film obtained by accumulating 30 layers on the quartz glass substrate obtained in this example, and the absorption peak is 43%.
At 6 nm. (3) Measurement of Nonlinear Optical Characteristics of Thin Film Element Next, the nonlinear optical characteristics of the sample thin film element manufactured as described above were confirmed according to the method described below. Here, evaluation was performed by focusing on optical second harmonic generation (SHG) as the nonlinear optical effect.

In this embodiment, the following device was used as a device for measuring optical harmonic generation. FIG. 5 is a block diagram schematically showing the measuring device. It is clear that the measuring device may have another configuration. In FIG. 5, reference numeral 1 denotes a laser light source that emits laser light. Here, a Nd: YAG pulse laser (wavelength: 1064 nm, pulse energy: 10 mJ) is used as a laser light source. The laser light source 1 is arranged so that the main surface of the sample element 8 is irradiated with laser light perpendicularly. 2 is a spectroscope for dispersing light generated from the sample 8,
In order to receive the light generated from the sample 8, the sample 8 is arranged so as to be opposed to the sample 8 by a laser light source 1 and the spectroscope 2 with a space therebetween. The spectroscope 2 is connected to the recorder 6 so that information indicating the wavelength at that time (wavelength information) can be recorded. Reference numeral 3 denotes a photomultiplier tube for making the light separated by the spectroscope 2 correspond to a current, 4 denotes a current amplifier for amplifying the current from the photomultiplier tube 3, and 5 denotes an integrator for averaging the amplified current. , 6 denote recorders for recording the values averaged by the integrator 5, respectively. Reference numeral 7 denotes a synchronization circuit for synchronizing the laser light source 1 and the integrator 5.

Next, a method of measuring the generated harmonic will be described. The light generated from the sample element 8 is split by the spectroscope 2 and the light is received by the photomultiplier 3. The spectroscope 2 has a variable resolution. In this embodiment, the spectroscope 2 sequentially scans at a certain resolution over a wavelength of 300 to 600 nm. Then, the wavelength information at that time is output from the spectroscope 2 to the recorder 6 each time. Further, a current corresponding to the light received by the photomultiplier tube 3 is made to correspond to the current, and this current is amplified by a current amplifier 4, averaged by an integrator 5 synchronized with laser oscillation, and recorded by a recorder 6. I do.
The spectrum of the light thus generated is obtained.

The thin-film element manufactured by the above-described manufacturing method is
When measured by this apparatus, as shown in FIG.
A strong optical second harmonic having a peak at 2 nm was observed.
FIG. 7 shows the results of measuring the SHG intensity by changing the incident angle with respect to the element surface at the time of p-polarization incidence. A clear fringe pattern due to interference of optical harmonics generated on the front and back surfaces of the quartz substrate was observed, and good quality was observed. It was found that a thin film was formed.

[0023]

As described above, according to the organic nonlinear optical material of the present invention, since it exhibits a nonlinear optical effect without inversion symmetry in a crystalline state, it can be used as an optical signal processing material.
It is also useful as an optical computer material. Further, according to the organic nonlinear optical thin film element of the present invention, the incident light emits light corresponding to the second harmonic and exhibits a remarkable nonlinear optical effect. When the SHG intensity is measured in a different manner, a clear fringe pattern can be obtained, indicating that a good quality thin film is formed. Therefore, the thin film element is useful for an element such as a light-to-light conversion element, a light modulation element, and an optical switch which will be produced by being incorporated in an optical waveguide. Further, it is also useful as a basic element for an optical computer that will be created by applying these elements.

[Brief description of the drawings]

FIG. 1 shows an infrared absorption spectrum of st-ANBA.

FIG. 2 shows an ultraviolet absorption spectrum of a chloroform solution of st-ANBA.

FIG. 3 shows a surface pressure-area curve of st-ANBA.

FIG. 4 shows an ultraviolet absorption spectrum of a st-ANBA thin film.

FIG. 5 is a block diagram showing a measuring device used for checking a nonlinear optical effect.

FIG. 6 shows an optical harmonic spectrum of a st-ANBA thin film element.

FIG. 7 shows a fringe pattern of a second harmonic emitted from the st-ANBA thin film element.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Minoru Saito 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (72) Masakazu Kato 1-7-12 Toranomon, Minato-ku, Tokyo No. Oki Electric Industry Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G02F 1/35 504 CA (STN) JICST file (JOIS)

Claims (2)

(57) [Claims] 1. An organic nonlinear optical material comprising a 5-alkylamino-2-nitrobenzoic acid represented by the following formula 1. Embedded image 2. An organic nonlinear optical thin film element comprising a thin film containing a 5-alkylamino-2-nitrobenzoic acid represented by the following formula 1. Embedded image