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

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 = H-2, 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 NIPS 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 [H-2 (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 [H-2(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.