Strategies to Enhance the Rate of Proton-Coupled Electron Transfer Reactions in Dye-Water Oxidation Catalyst Complexes

A thorough understanding of the proton-coupled electron transfer (PCET) steps that are involved in photocatalytic water oxidation is of crucial importance in order to increase the efficiency of dye-sensitized photoelectrochemical cells (DS-PEC) for solar to fuel conversion. This work provides a computational investigation of the ground and excited state potential energy surfaces of PCET reactions in two supramolecular dye-catalyst complexes for photocatalytic water splitting. The intrinsic reaction coordinate path is computed for the rate limiting PCET step in the catalytic cycle for both complexes. By using time-dependent density functional theory calculations, we show that the ground and excited state potential energy surfaces have a (near) degeneracy in the region of the PCET transition state. We discuss two possible strategies that take advantage of this feature to accelerate the PCET reaction: (i) through optimizing the conditions for vibronic coupling by chemical design and synthesis or (ii) through populating the product state with appropriately tuned laser pulses.