JP2861531B2 - Chiral nonlinear effect material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear optical material useful in fields such as optoelectronics, optical information processing, and optical communication.

[0002]

2. Description of the Related Art A nonlinear optical material is a material that exhibits a second-order or higher nonlinear response under a strong electric field of laser light, and is an important material in optical signal processing such as frequency conversion, oscillation, and switching. is there. In particular, tertiary nonlinear optical materials are attracting attention as key materials in next-generation optical communication and information processing that fully exhibit the excellent characteristics of light, such as high speed and parallelism. Among these nonlinear optical materials, organic nonlinear optical materials are particularly important because some of them have high-speed response and a large nonlinear optical constant as compared with conventional inorganic nonlinear optical materials. Although the mechanism of the manifestation of the third-order nonlinear optical effect has not been elucidated yet, it is known that, for example, those having a large delocalized π-electron system exhibit the third-order nonlinear characteristics. As a compound having a delocalized π-electron system, an aromatic compound (polyacene) in which aromatic rings are connected in a linear manner is known. However, such an aromatic compound has a problem that when the number of aromatic rings increases, the compound becomes thermally unstable, and the absorption wavelength of light shifts to a longer wavelength side.

On the other hand, the third-order nonlinear optical material attempts to utilize the fact that the refractive index changes with irradiation of light. As a method of reading the change in the refractive index, for example,
A method of amplifying a small refractive index change using a Fabry-Perrot resonator has been proposed, but in this method, the slight instability of the light source sensitively affects the resonance stability, so that the entire system is extremely delicate. The high dimensional quality accuracy required for stable operation of this device is an obstacle in terms of cost and mass production. In addition, extremely high energy must be injected in order to increase the refractive index change, and there are problems such as the heat resistance of the material, the heat barrier, the thermal effect, and the technical barrier for putting information on high injection energy. Was. As a method for improving this, a method has been proposed in which detection is performed with extremely high sensitivity by measuring elliptical polarization of weak probe light. In this method, a strong excitation light induces optical anisotropy in a substance to cause a change in polarization in a linearly polarized signal light. In this method, it is necessary to make the excitation light circularly polarized in order to utilize the optically induced optical anisotropy, or to incline the polarization direction of the excitation light from the polarization direction of the signal light. There were restrictions on the method.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, exhibit a large third-order nonlinearity, have no thermal or optical damage by a laser, and read a change in refractive index. To provide a nonlinear optical material to which various signal processing methods can be applied.

The present invention relies on light intensity for linearly polarized light.
A chiral compound that has the property of rotating the plane of polarization in the presence of
And chiral nonlinear effect materials . The chiral compound of the present invention preferably has a large delocalized π-electron system and a large optical rotation. As such a chiral compound, a chiral compound having a condensed aromatic ring is preferable, and examples thereof include optically active helicenes and exciton chirality compounds. Optically active helicenes include carbohelicene and heterohelicene. Carbohelicene is a compound having a helical structure in which 5 or more, preferably 6 to 20 aromatic rings are connected. Further, heterohelicene is a compound comprising a co-condensed ring of benzene and a hetero ring such as thiophene, furan, pyridine, pyrrole and the like. Further, carbohelicene or heterohelicene may have an aromatic ring or a heterocyclic ring with various substituents. Such carbohelicene and heterohelicene are, for example, Top.Curr.Chem.125 (St.
ereochemistry), 63-130 (1984). The method for synthesizing carbohelicene and heterohelicene is not particularly limited. For example, 1,2-diarylethylenes, bis (arylvinyl) ar synthesized by Wittig reaction or Siegrist reaction
It can be obtained by photocyclization of enes and the like. Since the helicenes have a large delocalized π-electron system, they exhibit a large third-order nonlinearity and are free from thermal and optical damage caused by a laser, and are therefore excellent as third-order nonlinear optical materials.

The exciton chirality compounds include two or more condensed aromatic chromophores each having two or more, preferably three to six, condensed aromatic rings, and strong asymmetric excitation between the condensed aromatic chromophores. And asymmetric compounds having a child interaction. For example, (6R, 15R)-(+)-6,15-dihydro-6,15-ethanonapht
ho [2,3-c] pentaphene, 13,13'-spirobi [13H-indeno [1,2
-b] anthracene] and 1,1'-bianthryl derivatives. Such exciton chirality compounds,
For example, described in Noriyuki Harada and Koji Nakanishi, circular dichroism spectrum-application to organic stereochemistry-, Tokyo Kagaku Dojin (1982) and New Experimental Chemistry 13, Organic Structure II, p850-879, Maruzen (1977). Have been. Further, a condensed aromatic chromophore of the exciton chirality compound may be added with a donor or an acceptor or a π-conjugated substituent to promote delocalization due to exciton interaction or π-conjugation. "

Since the chiral nonlinear effect material of the present invention has chirality, it has the property of rotating the plane of polarization of linearly polarized light depending on the intensity of light. Hereinafter, the principle of expression in which the plane of polarization rotates with respect to linearly polarized light will be described. FIG. 1 shows the CD spectrum of (+)-hexahelicene, which is a chiral nonlinear optical material, and FIG. 2 shows the ORD spectrum. In the CD spectrum, a positive peak was observed at around 330 nm, and there was strong absorption of left-handed circularly polarized light (L).
A negative peak is observed in the vicinity, and there is strong absorption of clockwise circularly polarized light (R). In the ORD spectrum, the signs are inverted around these wavelengths. From this, when the chiral compound is represented by an extremely simplified model, it is considered that the chiral compound has different energy levels for the L-polarized light and the R-polarized light as shown in FIG. In this case, the absorption spectrum and the refractive index dispersion have a frequency shift with respect to the L-polarized light and the R-polarized light as shown in FIGS. Assuming that the refractive index for L-polarized light is n _L and the refractive index for R-polarized light is n _R , the optical rotation is (n _L −) as shown in FIG.
caused by n _R), polarization rotation angle is made the sample length l, as a wavelength lambda? 1 / lambda and (n _L -n _R). Next, when the nonlinear refractive index change is caused by the strong linearly polarized light excitation, the linearly polarized light is considered to be a combination of left and right circularly polarized light, and thus acts on both n _L and n _R ,
The refractive index changes as shown in FIG. 4B (dotted line). Assuming that the nonlinear refractive index changes are Δn _L and Δn _R , the polarization rotation angle due to the nonlinear effect is πl / λ [(n _L −n _R ) − {(n _L + Δn _L ) − (n _R + Δn _R )}. ] = Π1 / λ (Δn _L −Δn _R ). That is, it is considered that polarization rotation occurs according to the difference between the non-linear refractive index changes for the L-polarized light and the R-polarized light. This effect is expected to increase as the optical rotation increases.

Accordingly, when the chiral nonlinear effect material of the present invention is irradiated with linearly polarized light, it can be detected as a change in the rotation angle of the polarization plane by changing the light intensity. By utilizing this characteristic, if the above-mentioned elliptic polarization analysis method is used, the same measurement can be performed with linearly polarized light in the same direction as the signal without devising polarization as the excitation light. Processing becomes possible. Further, the excitation light and the signal light are converted into one linearly polarized light, and the signal waveform can be controlled by self-rotation based on the light intensity. Further, by using a high repetition pulse light source, higher sensitivity and accuracy can be secured in combination with a high-frequency polarization modulation element. Therefore, it can be suitably used as a device material for optical communication, optical information processing and the like.

[0009]

Embodiments are described below. Example 1 A small amount of iodine was added to a 0.2 g / l benzene solution of 2,7-bis (styryl) naphthalene, which was irradiated with light using a high-pressure mercury lamp for 2 hours. Recrystallization using ethanol as a solvent,
(±) -Hexahelicene was obtained. Next, hexahelicene was optically resolved by the HPLC method. The obtained (+)-
The optical purity of hexahelicene and (−)-hexahelicene was 100%. Using the obtained (+)-hexahelicene, a polarization / nonlinear constant measuring device shown in FIG.
The measurement of the chiral nonlinear effect was performed. The signal light is a polarizer P
After passing through the sample after being converted to linearly polarized light by the analyzer 2, the analyzer P3
Quenched by Here, when the sample was irradiated with linearly polarized light excitation light having the same polarization direction as the signal light by the polarizer P1, seepage light due to the chiral nonlinear effect was detected.

Example 2 (-)-Hexahelicene obtained in Example 1 and (±)
-Using hexahelicene, the chiral nonlinear effect was measured by the polarization / nonlinear constant measuring apparatus shown in FIG.
The signal light is linearly polarized by the polarizer P2, passes through the sample, and is then quenched by the analyzer P3. Here, the sample was irradiated with linearly polarized excitation light having the same polarization direction as the signal light by the polarizer P1 while changing the intensity, and the intensity of the exuded light due to the chiral nonlinear effect was detected. FIG. 6 shows the relationship between the intensity of the seeping light and the intensity of the linearly polarized excitation light.
From the figure, it can be seen that in the case of (−)-hexahelicene, seepage light is detected, but not for (±) -hexahelicene. FIG. 6 shows the result of measurement of the nonlinear effect by circularly polarized excitation light for reference.

[Brief description of the drawings]

FIG. 1 is a diagram showing a CD spectrum of (+)-hexahelicene.

FIG. 2 is a diagram showing an ORD spectrum of (+)-hexahelicene.

FIG. 3 is a diagram showing energy levels of a simplified model of a chiral compound with respect to L-polarized light and R-polarized light.

FIG. 4 is a diagram showing an absorption spectrum, refractive index dispersion, optical rotation, and nonlinear polarization rotation of a chiral compound for left and right circularly polarized light.

FIG. 5 is a schematic diagram of a polarization / nonlinear constant measuring apparatus.

FIG. 6 is a diagram illustrating a relationship between the intensity of the exuding light and the intensity of the seeping light in the measurement of the nonlinear effect.

Claims (4)

(57) [Claims] 1. A chiral nonlinear effect material comprising a chiral compound having a property of rotating a plane of polarization depending on the intensity of light with respect to linearly polarized light. 2. The chiral nonlinear effect material according to claim 1, wherein the chiral compound has a fused aromatic ring. 3. The chiral nonlinear effect material according to claim 1, wherein the chiral compound is an optically active helicene. 4. The chiral nonlinear effect material according to claim 1, wherein the chiral compound is an exciton chirality compound.