Computational Characterization of Competing Energy and Electron Transfer States in Bimetallic Donor- Acceptor Systems for Photocatalytic Conversion
Lisa A. Fredin, Petter Persson
The rapidly growing interest in photocatalytic systems for direct solar fuel production, such as hydrogen generation from water splitting through so-called artificial photosynthesis, is grounded in the unique opportunity to achieve charge separation in molecular systems provided by electron transfer processes. Recent, significant experimental and theoretical efforts to better understand and control photoinduced electron transfer processes in a wide variety of relevant supramolecular and heterogeneous systems has led to more efficient light harvesting and catalytic metal centered complexes. In general, both photoinduced and catalytic processes involve complicated dynamics that depend on both structural and electronic effects. Quantum chemical calculations provide detailed theoretical information concerning many key aspects of photoinduced electron and excitation transfer processes in supramolecular donor-acceptor systems, which are particularly relevant to better understand fundamental charge separation processes in emerging molecular approaches for solar energy conversion. Here density functional theory (DFT) calculations explore the excited state landscape of metal centered light harvester-catalyst pairs. In weakly bound systems, the interplay between structural and electronic factors involved can be constructed from the various mononuclear relaxed excited states. For this study, supramolecular states of energy transfer and excitation transfer character have been constructed from constituent full optimizations of multiple charge/spin states for a set of three light harvesters and ten catalysts in terms of energy, structure, and electronic properties. This method is a quick, cost effective screening tool for identifying underlying issues of donor-acceptor pairs for photoinduced electron transfer applications.