Ruthenium complexes bearing terpyridyl ligands of distinct donor-acceptor configuration for solar energy conversion

A novel series of heteroleptic ruthenium complexes employing a butyl-functionalized terpyridine (tpy) as a donor and tpy functionalized with up to three carboxylic acid groups as acceptors are prepared. Structural tailoring of these complexes helped not only to tune the photo-excited-state lifetimes but also aided in accumulating electron density through the anchoring groups. Wider separation between the triplet metal-to-ligand charge transfer (³MLCT) state and the metal-centered states is achieved while maintaining a reasonable barrier between the S₀ ground and the ³MLCT states. This electronic state alignment facilitated the electron injection into TiO₂ photoanodes from the excited states of complexes. The structural configuration comprising a butyl-tpy donor and three carboxylate-functionalized tpy acceptors around the ruthenium center ensured faster interfacial electron transfer (IET) and charge dissipation into the TiO₂ clusters to longer diffusion lengths. This work presents a facile synthetic route to access these push-pull complexes and evaluates their use as molecular photosensitizers via a combined experimental and computational approach. Quantum dynamics simulation results demonstrate the extent of vectorial electron transfer from these complexes into the TiO₂ cluster.