ALL-INORGANIC POLYNUCLEAR UNITS FOR CLOSING THE PHOTOSYNTHETIC CYCLE

摘要

Artificial photosynthetic systems made of all-inorganic components are attractive from a durability standpoint, but the use of solid inorganic materials faces the challenge of facile and precise tuning of the electronic properties of the photoactive components. We have developed an inorganic molecular approach by assembling oxo- bridged heterobinuclear light absorbing units covalently anchored on a silica nanopore surface. A dozen different units utilizing mostly first row transition metal centers, e.g.TiOCo(II) have been synthesized and characterized in the last several years. The units are anchored on the nanochannel surfaces of mesoporous silica such as SBA-15, or on the convex surface of silica nanoparticles. They possess a visible light absorbing metal-to-metal charge transfer transition (Ti(IV)OCo(II) ? Ti(III)OCo(III)) suitable for driving a multi-electron catalyst for water oxidation coupled to the donor center, or for activating a reduction reaction on the acceptor side. With a wide range of metal centers to select from, the redox potential of donor and acceptor centers can be matched with the potential of the catalyst. We have reported earlier a binuclear chromophore, TiOCr(III), driving an IrOx nanocluster catalyst for water oxidation in aqueous solution as a half reaction. For photoreduction, ZrOCu(I) and more recently ZrOCo(II) units were found to split CO2 to CO upon MMCT excitation.