Two‐Channel Model for Electron Transfer in a Dye‐Catalyst‐Dye Supramolecular Complex for Photocatalytic Water Splitting

To improve the performance of dye‐sensitized photoelectrochemical cell (DS‐PEC) devices for splitting water, the tailoring of the photocatalytic four‐photon water oxidation half‐reaction represents a principle challenge of fundamental significance. In this study, a Ru‐based water oxidation catalyst (WOC) covalently bound to two 2,6‐diethoxy‐1,4,5,8‐diimide‐naphthalene (NDI) dye functionalities provides comparable driving forces and channels for electron transfer. Constrained ab initio molecular dynamics simulations are performed to investigate the photocatalytic cycle of this two‐channel model for photocatalytic water splitting. The introduction of a second light‐harvesting dye in the Ru‐based dye‐WOC‐dye supramolecular complex enables two separate parallel electron‐transfer channels, leading to a five‐step catalytic cycle with three intermediates and two doubly oxidized states. The total spin S=1 is conserved during the catalytic process and the system with opposite spin on the oxidized NDI proceeds from the Ru=O intermediate to the final Ru‐O(2) intermediate with a triplet molecular (3)O(2) ligand that is eventually released into the environment. The in‐depth insight into the proposed photocatalytic cycle of the two‐channel model provides a strategy for the development of novel high‐efficiency supramolecular complexes for DS‐PEC devices with buildup and conservation of spin multiplicity along the reaction coordinate as a design principle.