Mitsuru Yoneyama

Excitation energy transfer in Langmuir–Blodgett films of 5-(4-N-octadecylpyridyl)-10,15,20-tri-p-tolylporphyrin on gold-evaporated glass substrates studied by time-resolved fluorescence spectroscopy

Abstract The fluorescence decays in mono- and multilayer Langmuir–Blodgett (LB) films of 5-(4-N-octadecylpyridyl)-10,15,20-tri-p-tolylporphyrin (porphyrin 338a) deposited on gold-evaporated glass substrates were measured to explore various channels for excitation energy transfer processes. The decays in the 1-layer LB films of porphyrin 338a separated from gold surface by LB film of arachidic acid were also measured as a function of the thickness of the spacer, i.e. thickness of the LB films of arachidic acid. Consistent with our previous steady-state fluorescence study, the expectation values of the lifetime obtained by fitting the decay curves with two exponential functions for the LB films indicate that at the short separation distance, the energy transfer from the porphyrin molecules to the gold surface overshadows other processes, including intra- and interlayer energy transfers. The deviation of energy transfer rate from Chance et al. (CPS) prediction of inverse distance cubed in our case may be interpreted by assuming the presence of additional excitation energy decay pathways in the LB films of porphyrin 338a on the gold-evaporated glass substrates.

OPTICAL MODIFICATION OF WAVE DYNAMICS IN A SURFACE LAYER OF THE MN-CATALYZED BELOUSOV-ZHABOTINSKY REACTION

Abstract The effect of visible light on a thin layer of Mn-catalyzed Belousov-Zhabotinsky reaction solution covered with a Ru(bpy) 3 2+ monolayer is investigated. Intense illumination strongly affects the spatiotemporal behavior of chemical waves on the monolayer surface, inducing counterpropagating or phase-shifted wave pecies in the illuminated area. The illumination effect is observed only in a surface layer of the solution, which implies that some photochemical reactions at the monolayer-liquid interface play an important role. These experimental results are compared with numerical simulations based on the Oregonator model.

Thermal behavior of Langmuir–Blodgett films of 5-(4-N-octadecylpyridyl)-10,15,20-tri-p-tolylporphyrin studied by ultraviolet-visible and infrared spectroscopies

Abstract Thermal behavior of Langmuir–Blodgett (LB) films of 5-(4- N -octadecylpyridyl)-10,15,20-tri- p -tolylporphyrin (porphyrin 338a) was investigated by use of ultraviolet-visible (UV-vis) and infrared (IR) spectroscopies. With increasing temperature from 30°C to 170°C, Soret bands of one- and nine-layer LB films of porphyrin 338a on CaF 2 substrates show a blue shift by 6 and 2 nm, respectively. In contrast, a Q(x)(0,0) band shows a red shift by 10 and 5 nm, respectively, for the one- and nine-layer LB films. The one-layer LB film shows more significant shifts of the Soret and Q(x)(0,0) bands than the nine-layer film, indicating different thermal behavior of the porphyrin aggregates, which may be induced by different effects of interaction between the substrate and the first monolayer, and by the existence and nonexistence of interlayer interaction. In the IR spectra of a nine-layer LB film of porphyrin 338a on a CaF 2 plate, the frequencies of CH 2 antisymmetric and symmetric stretching bands increase significantly with temperature, suggesting the increase in gauche conformers in the hydrocarbon chain of the porphyrin 338a. In contrast, the frequencies of bands arising from the porphyrin macrocycle and attached pyridyl groups decrease gradually with the increase in temperature. These observations indicate deformation of porphyrin core and changes in coplanarity of the pyridyl groups with the porphyrin plane.

Chemical oscillations in Ru byp 2+ 3 Langmuir monolayers formed on Belousov-Zhabotinskii reaction solutions

Abstract A new approach to external perturbation and control of two-dimensional pattern structures in Langmuir monolayers is presented. The method utilizes the conventional Belousov-Zhabotinskii (BZ) chemical oscillator as a subphase for monolayer formation. It is found, by using fluorescence microscopy, that propagating chemical waves are formed in Ru(bpy)32+ monolayers on Ce4+-catalyzed BZ reaction solutions, reflecting periodic Ce4+Ce3+ changes in the subphase. This system shows high sensitivity to illumination with visible light, and inhibition of wave propagation is clearly observed in the microscopic field.

Fluorescence microscopic studies of spatial structures in Ru(bpy)32+ monolayers

Abstract The direct visualization of Ru(bpy)32+ monolayers spread on cerium-catalyzed Belousov-Zhabotinskii (BZ) reaction solutions has been made by fluorescence microscopy. Polarized luminescence observations show that with ClO4− counterions contained in the subphase, the monolayer is composed of bright crystalline domains with high optical anisotropy. On this luminescent monolayer, spatial patterns are found to evolve with time as propagating dark waves in response to oscillatory chemical reactions in the BZ subphase.

Optical neural device based on memory-type organic photoconductors

A variable-sensitivity organic-photoconductive device has been developed by using a memory-type organic photoconductor. The device is composed of an input layer and a memory layer acting as a charge generation and a charge transport layer, respectively. A persistent high-sensitivity state, which corresponds to a modulation of synaptic weights in a neuron model, was obtained by blue light illumination. A photochemical reaction of thiomichlers ketone (TMK) in the memory layer was found to be responsible for the memory formation. As a potential application of this memory-type organic photoconductor to an optical neural device, 2-D pattern storage and calculations were performed successfully.