Photoelectrochemical Responses from Zinc Porphyrin-Silver Nanoparticle Composite Films Fabricated on ITO Electrodes

The fabrication of zinc tetraphenyl porphyrin (ZnTPP)–silver nanoparticle (AgP) composite films on indium–tin-oxide (ITO) electrodes were carried out by the electrostatic layer-by-layer adsorption technique. The degree of immobilization of AgPs on the ITO electrodes could be controlled by changing the immersion time into the aqueous colloidal solution of AgPs. Maximum enhancement in the photocurrent action spectra as well as the fluorescence emission spectra was observed when optimum amounts of AgP were deposited onto the ITO electrode for the photocurrent and the fluorescence measurements, respectively. Effect of AgP on the photocurrent and the fluorescence suggested the effects of enhanced electric fields resulting from the localized surface plasmon resonance on the enhancement of photocurrent and fluorescence signals. The effect of AgP on the lifetime of the singlet excited state of ZnTPP (¹ZnTPP*) indicated that the lifetime of ¹ZnTPP* becomes shorter at an immersion time of 6 h. The results of the fluorescence lifetime suggested that the difference of effects of AgP on the photocurrent and the fluorescence is most likely ascribed by that the energy-transfer from ¹ZnTPP* to surface plasmon due to AgP aggregates is competitive with the photoinduced electron-transfer from ¹ZnTPP* to O₂ in the photocurrent measurements