Studies on Electrodes Modified by Noble Metal Nano-Particles Covered with Dye Aggregate

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The strength of absorption band of Frenkel exciton in J-aggregates of cyanine dyes on noble metal nano-particles (J-aggregate/noble metal nano-particles) is affected by the surface plasmon excited in the nano-particles. In this study, we tried to construct the J-aggregate/noble metal nano-particles on electrode, and we examined the possibility of the electrode for photo-electrochemical methods. Until this study, we have prepared the noble metal nano-particles on mica, which have the atomically flat surface. However, in the case of using other substrate whose surface would be rougher than mica, the best condition for making nano-particles was different. Therefore, we first searched for the best condition to make nano-particles by vacuum evaporation coating. As a result, although the size distribution of the particles was not so good, we could prepare the noble metal nano-particles, which have a desired plasmon band, on the substrate. We confirmed that J-aggregate of cyanine dye could adsorb on the noble metal nano-particles by using halogenations method or SAMs of aminothiol. However, the delamination of nano-particles from the substrate often occurred when the substrate with nano-particles was immersed in solutions. In case of using Ar ion sputter coating to prepare the noble metal nano-particles on the substrate, the nano-particles were less delaminated from the substrate during immersing process than the case of using vacuum evaporation coating. As a result, it became to possible to construct the J-aggregate/noble metal nano-particles on the electrode and to examine the photo-electrochemical properties. On the other hand, we measured the fluorescence decay curves and transient absorption spectra of the J-aggregate/noble metal nano-particles system, and obtained the new insight for the relaxation dynamics of the excited state of the system. Because photo-electrochemical process starts from the excited state of the system, it is important to know the dynamics.