Energy-Controlled Spaces at the Single-Molecule Photo-Hydrogen-Evolving Devices

点击翻译按钮获取中文摘要

Great attention has been paid to the studies on the photocatalytic systems promoting the solar-light-induced splitting of water into H_2 and 1/2O_2, because water and sunlight are abundant and such systems are free of the CO_2 emission. Since the original discovery in the H_2-evolving activities of amidate-bridged Pt(II)_2 dimers having a relatively strong metal-metal interaction, considerable efforts have been made to develop the 'photo-hydrogen-evolving (PHE)' molecular devices (MDs) that are made up of photosensitizing Ru(bpy)_3^<2+> derivatives and H_2-evolving Pt(II) catalysts. Such PHEMDs are expected to serve as an efficient 'photocatalyst'towards the visible-light-induced reduction of H_2_O by EDTA into H_2. As a result, we discovered that one particular molecular device consisting of a [Ru(bpy)_2(5-amino-phen)]^<2+> unit and a PtCl_2(bpy) unit evolves H_2 in the presence of EDTA under the visible light illumination.In this project, several other related compounds have also been prepared and evaluated to better understand the factors affecting the PHE activities of such PHEMDs These studies suggested the following key factors: (i) destabilization of the HOMO corresponding to the filled Pt(II) dz^2 orbital enhances the PHE activity; (ii) steric hindrances around the axial site of the square-planar Pt(II) coordination sphere lower the PHE activity; (iii) an appropriate aromaticity is needed to enhance the intramolecular electron transfer processes; (iv) EDTA forms an adduct with a PHEMD before undertaking the H_2 generation; (v) the H_2 formation undergoes via a bimolecular process of the PHEMD. In addition to these results, the electrochemical studies, stopped flow experiments looking at the reactions between the Pt(II) complexes and a radical cation generated from methylviologen, and DFT MO investigations have been examined.