An efficient oxidation at photofunctional interface of phthalocyanine in combination with fullerene

When metal-free phthalocyanine (H2Pc, a p-type semiconductor) was used in combination with fullerene (C60, an n-type semiconductor), it was confirmed that the bilayer film of C60/H2Pc functioned as a novel and efficient photoanode in the water phase. The photoinduced oxidation of thiol occurred at the H2Pc/water interface along with hole conduction through the H2Pc layer, and based on the photophysical character of the bilayer. The typical photoelectrode characteristic involved a transient photocurrent occurring in the initial stage under illumination (under potentiostatic conditions), following which the photocurrent reached a steady-state. Such transient photoelectrochemical features at the H2Pc/water interface were investigated with respect to the thiol concentration, from which it was noted that both the initial spiky photocurrents and the steady-state photocurrents showed saturation at higher concentrations. An analysis with photoelectrode kinetics was performed by assuming an adsorption step prior to a rate-limiting charge transfer step. In the analysis, equations were applied to such photocurrents based on the Langmuir adsorption equilibrium. Kinetic analysis also revealed the kinetics for the thiol oxidation to be ca. 20 times faster in the present bilayer than that in a single layer of a hole-photoconducting phthalocyanine. This showed that the phthalocyanine in the organic bilayer works as an efficient photofunctional interface in the water phase.