Visible light-induced electron transfers in titania nanosheet and mesoporous silica integrated films

Abstract

Two spatially different nano-structured inorganic materials, titania nanosheets (TNS) and mesoporous silica (MPS), were integrated onto a glass substrate to form stacked composite thin films. Investigations were then carried out on photoinduced electron transfers between the tetrakis(1-methylpyridinium- 4-yl)porphyrinatometal(4+) ion ([M-(tmpyp)]4+); M = H2, Zn, and Co) and 1,1′-dimethyl-4,4′-bipyridinium (methyl viologen; MV2+) within the hybrid films. The [M(tmpyp)]4+ molecules were found to be adsorbed only in the MPS nano-cavities, while MV2+ was intercalated only in the TNS layer, i.e., the [M(tmpyp)]4+ and MV2+ molecules could be separately and selectively accommodated into the MPS nano-cavities and TNS layers of the hybrid films, respectively. Upon UV light irradiation (TNS excitation) of the films containing [H 2(tmpyp)]4+, the decomposition of [H2(tmpyp)] 4+ and the formation of a one-electron reduced MV2+ (MV+•) were observed, clearly indicating photoinduced electron transfers in the MPS/TNS films. Moreover, when the metal-complex [Zn(tmpyp)]4+ or [Co(tmpyp)]4+ was used in place of [H2(tmpyp)]4+, visible light-induced electron transfers could be observed in the present MPS/TNS hybrid films, the first report of such charge separation in consecutively stacked thin films by visible light. © 2006 The Chemical Society of Japan.