Tetsuya Aoyama

Photorefractive effect from photo-induced orientation of a novel carbazole derivative

Two-beam coupling gain obtained from an orientational index grating was observed without applying an external field in a photorefractive polymeric material with ow glass transition temperature. A novel carbazole derivative with a photorefractive function was used as the material doped with a sensitizer for photocarrier generation. The mechanism to form the grating and to give the gain was investigated by two-beam coupling measurements.

Xerographic and Electro-Optic Studies of a Photorefractive Polymer

Abstract We examined both photoconductive and electro-optical properties of the monolithic photorefractive polymer. The photoconductive sensitivity of 1.2 × 10−12(S cm−1)/(W cm−2) was obtained under a field strength of 5 × 105V/cm and a wavelength of 534nm. The EO signals linearly increased with the poling electric field.

Photoconductive and electro-optic responses in multifunctional carbazole polymers

Photocarrier generation properties and an electro-optic response were studied in acceptor-substituted carbazole materials. Two kinds of carbazole systems were investigated: molecularly doped polymer and main-chain polymer. The photoconductive sensitivity of 1.2x1012(S cm1)I(W cm2) was obtained with a field strength of 5x1O5V/cm at a wavelength of 534nm. The electro-optic coefficient 33 of l.lpmJV was obtained with a field strength of 5x1O5V/cm at a wavelength of 532nm. These results show the monolithic photorefractive polymer could be developed by using acceptor-substituted carbazoles.

Three-dimensional (3D) concave OLEDs fabricated by a multilayer coating technique of electrospray deposition (ESD)

Organic light-emitting diode (OLED) materials were deposited directly on a concave glass surface using the electrospray deposition (ESD) technique to obtain three-dimensional (3D) multilayer OLEDs. Deposition without dissolving the underlying layer was realized by tuning the mixture ratio of the mixed solvents. A simulation of the electric force lines was used to assist in obtaining a uniform deposition on a 3D-curved substrate. The active layers of the OLED were sequentially prepared on watch glasses by the ESD technique. A green light emission from the concave device indicates that the ESD technique is a viable solution-processing technique for developing 3D multilayer OLEDs.

Second- and third-order nonlinear properties of chiral phthalocyanine films

Vanadyl phthalocyanine derivatives having optically active side chains and the corresponding racemic isomers were synthesized and examined as nonlinear optical materials. These dyes were soluble in organic solvents and gave uniform thin films using spin coating. The thin films (neat or polymer doped) of each phthalocyanines showed the second- and third-order nonlinear optical responses under appropriate experimental conditions. The nonlinear optical susceptibilities of the optically active derivatives are larger than those of the corresponding racemic isomers. To clarify this enhancement phenomenon, we measured the electronic absorption- and circular dichloic spectra, and X-ray diffraction of the thin films. These results suggested that the optically active dyes forms one-dimensional columnar aggregates with one-handed helical sense and the columns further aligned into honeycomb-like chiral superstructures. It was surmised from the experimental results that the chiral superstructures enhance the nonlinear optical responses relative to the racemic analogues.

Photorefractive properties of conjugated carbazole polymers

We discussed the electric and optical properties of three types of conjugated carbazole polymers: substituted polyacetylene with carbzole moiety, main-chain polymers having conjugated carbazole trimer units, and triindole units. Substituted polyacetylenes can be expected to show the enhanced optoelectronic responses due to the extended conjugated systems in the main chain and the additional chromophores in the side chain. The hole mobility of a substituted polyacetylene containing carbazole moiety was determined to be about 10-4 cm2/Vs with the electric field of 4 x 105 V/cm by time-of-flight technique, while polyvinylcarbazole showed hole mobility of about 10-6 cm2/Vs. The carrier mobility is presumably enhanced by the extended conjugation system. Hyperbranched polymers with carbazole trimer units exhibited the enhanced two beam coupling gain of 60 cm-1 in comparison with main-chain polymer with carbazole units. Since triindole is an electron-donative molecule containing three carbazole substructures with smaller ionization energy than that of carbazole, we can expect the application to a variety of optical and electrical materials. Main-chain polymers with triindole units exhibited the two-beam coupling gain of over 100 cm-1. Therefore, theses conjugated carbazole polymers are one of the good candidates for the new class of electronic and photonic materials.

Thermally stimulated current and electro-optic responses in photorefractive polymers

We describe the depolarization of photorefractive polymers by means of thermally stimulated current (TSC) and electro-optic responses. The film was prepared by spin-coating from a chloroform solution onto an ITO substrate, and dried overnight at 500 C under vacuum. For TSC measurements, the poled polymer samples were heated at a constant heating rate of 3 C/min. The resulting depolarization current was measured using a Keithley 6512 electrometer. The EO response of the poled photorefractive polymer was measured by the reflection method.

Multifunctional carbazole oligomers and polymers for photorefractive applications

The photorefractive properties of the carbazole films were characterized by two-beam coupling and four-wave mixing. We have demonstrated the optical image reconstruction of distorted images due to phase conjugation using a four-wave mixing setup, the optical associative memory based on phase conjugation and the angle multiplexed holographic recording. We present an example of the optical associative memory using a conjugated carbazole trimer film. The film stores the hologram images by multiple exposure in the bulk. When the imperfect image is introduced to the film, the beam is diffracted to the direction of strongest interaction with the perfect image and behave as a probe beam. The reference beam is reflected by the phase conjugation mirror and produces the perfect image.