Construction of Highly Hierarchical Layered Structure Consisting of Titanate Nanosheets, Tungstate Nanosheets, Ru(bpy), and Pt(terpy) for Vectorial Photoinduced Z-Scheme Electron Transfer.

To imitate the precisely ordered structure of the photoantennas and electron mediators in the natural photosynthesis system, we have constructed the Ru(bpy)-intercalated alternate-layered structure of titanate nanosheets and tungstate nanosheets via thiol-ene click reaction. Before nanosheet stacking, Pt(terpy) was immobilized at the edge of the titanate nanosheets. The visible-light-induced vectorial Z-scheme electron transfer reaction from the valence band of tungstate to the conduction band of titanate via the photoexcited Ru(bpy) was demonstrated by the following two evidences: (1) From the results of the fluorescence decay of Ru(bpy), the rate of the forward electron transfer from the photoexcited Ru(bpy) to the conduction band of titanate was estimated as 1.16 × 10 s, which was 10 times faster than the backward electron transfer from the photoexcited Ru(bpy) to the conduction band of tungstate (1.02 × 10 s) due to a localization of Ru(bpy) on the titanate nanosheets. (2) We observed the decrease of the electrons accumulated in the conduction band of the tungstate induced by photoexcitation of Ru(bpy), demonstrating the forward electron transfer from the conduction band of tugnstate to the vacant highest occupied molecular orbital level of the photoexcitation Ru(bpy). Finally, H gas was produced from the water dispersion of the alternate-layered structure under visible light irradiation, suggesting that the electrons getting to the conduction band of the titanate were transferred to the Pt(terpy) placed at the edge of the nanosheets, and reduced water to dihydrogen. Herein, n-octylamine species at the interlayer space played a role as hole scavenger; in other words, these molecules were oxidized by the hole in the conduction band of the tungstate nanosheets.