Tetsuo Murayama

Cross-Linked Poled Polymer: Poling and Thermal Stability

Cross-linked poled polymers were studied with a methacrylate polymer containing chromophores and epoxide groups as side chains. The cross-linking and poling processes were monitored by electrooptic (EO) measurement. Contribution of molecular motions of the chromophores was observed with low-frequency AC electric field. This contribution decreased as the cross-linking reaction proceeded, and was found to be a good monitor of poling with cross-linking. The resultant cross-linked poled polymers showed significant improvement of thermal stability. The stability was studied by changing the concentrations of cross-linking agents, curing temperatures, and type of cross-linking agent.

Memory effect of an organic photoconductor and its application to a neuron model

A new type of organic photoconductor composed of 9‐ethylcarbazole‐3‐carbaldehyde diphenylhydrazone (DPH) dispersed in a polycarbonate polymer (PCR) film, when in the presence of thio‐Michler’s ketone (TMK), was found to exhibit a sustained state of enhanced conductivity following visible irradiation. At room temperature, the enhanced current is observed to decay slowly over a period of a day and when heated it rapidly returns to its original state. A potential application of this ‘‘memory’’ effect to an artificial neuron model, using such memory‐type organic photoconductors as optically controllable interconnections, is discussed. A liquid‐crystal cell is used to demonstrate a nonlinear‐saturated response dependent on a weighted input electric signal.

Fabrication of photodiode arrays by molecular assembly technique

Mixed monolayers of 5‐(4‐N‐decylpyridinium)‐10,15,20‐tri‐p‐tolyl porphyrin (PyP) and arachidic acid (AA) were prepared on a water surface as a precursor for organized arrays of photodiodes. By compression and expansion of the films, PyP self‐assembled to form nearly circular domains with their size dependent on the molar ratio of PyP and AA. These structures were successfully incorporated into Schottky‐type cells, and their photoelectric properties were studied on the domain level by illumination of a focused light with a diameter of 20 μm. The short‐circuit photocurrents showed large fluctuations depending on the position of illumination, which reveals that the PyP domains function as photodiode arrays.

Novel naphthoquinone methide dyes for second-order nonlinear optical materials

Naphthoquinone methide dyes show a large Pockels coefficient at 1.3 µm when poled in a polymer matrix: the second-order nonlinear hyperpolarizability (µβ) values obtained from Pockels coefficients that appear after poling in a constant electric field are (5700–7400)× 10–48 esu, being much higher than that of commonly used Disperse Red 1 (DR1).

Novel naphthoquinone methide dyes for poled polymers

We propose a novel type of chromophore, naphthoquinone methide dyes, for nonlinear optics used in the near IR wavelength. The large resonance effect and the small intermolecular interaction allows the chromophore to show a large Pockels coefficient at 1.3 micrometers when it is poled in a polymer matrix. The origin of the nonlinearity is discussed by measuring the ground state dipole moment and the change in dipole moment between the ground and excited states. The polyurethane to which this dye was chemically attached was synthesized and the large nonlinearity was demonstrated. In polymer films, propagation loss at 1.3 micrometers increases maybe due to the aggregation of chromophores.

Surface-pressure-induced chromism in rhodamine monolayers

Abstract The optical properties of mixed monolayers incorporating a surface-active rhodamine B have been studied by using various subphases and matrices. When the proton concentration around the dye was low the visible absorption decreased completely at high surface pressures, whereas when the proton concentration was high the absorption decrease was incomplete and the contribution of high order aggregates was observed. These features are explained by a shift in the equilibrium between cation, zwitterion and lactone forms of rhodamine dye at the air-water interface.

Two-dimensional domain shape transitions in photosensitive monolayer assemblies

Bubble-stripe shape transitions of gaseous domains are observed in Langmuir monolayers of porphyrin/arachidic acid and porphyrin/spiropyran mixtures using fluorescence microscopy. Characteristics of the transition such as critical bubble size are found to be controllable by subphase pH or UV/visible irradiation. These features are discussed in terms of a balance between dipolar repulsions and line tension in the monolayer.

Microstructure-Dependent Photoelectric Properties in Porphyrin LB Films

Abstract The microstructure-dependence of photoelectric properties have been studied for Langmuir-Blodgett (LB) films containing 5-(4-N-decylpyridinium)-10, 15, 20-tri-p-tolyl porphyrin (PyP) and arachidic acid (AA). Two-dimensional distribution profiles of short-circuit photocurrent (Isc) exhibited clear bumps and valleys for the LB films with large PyP or AA domains. The spatial averages of Isc tended to show lower values for smaller domain structures, suggesting a great contribution of carrier recombination at the PyP-AA interface.

Transient Carrier Injection in Layered Organic Photoconductors

Transient photocurrents within layered organic photoconductors using copper phthalocyanine and hydrazone derivatives were measured with two different means of carrier generation: one contained a carrier injection process between the two different layers and the other did not. By means of deconvolution of these two transients, the carrier injection rate was observed as a function of time. The injection rate of the layered photoconductor containing copper phthalocyanine and the hydrazone derivative had a long time tail. The observed low photoinjection efficiency of the transport material which possesses a high ionization potential is not attributed to recombination but to a broad distribution of carrier injection rates.