Ruthenium(II) complexes bearing polypyridyl ligands with amide bound thienyl groups for photochemical energy conversion

Mimicking natural photosynthesis requires long charge recombination lifetimes, spatial charge separation, and sufficient excited state energy to catalyze processes such as water splitting. Complexes bearing laminate acceptor ligands and ancillary diimine ligands with electron rich donor moieties are suitable candidates as reaction centers for photoinduced charge separation in artificial photosynthesis. In this work, new diimine ligands with thiophene oligomers appended via amide linkages are incorporated into metal polypyridyl complexes. Homoleptic Ru²⁺ complexes bearing 1,10-phenanthroline ligands with amide bound bithiophene units exhibit excited state behavior deviating significantly from that observed in [Ru(phen)₃][PF₆]₂ (30). The bithiophene unit fuels a long-lived excited state (τ ≈ 7 μs) in [Ru(phen-btL)₃][PF₆]₂ (32) through an energy reservoir effect, where ³LC and ³MLCT states are equilibrating in the excited state. A third ³ILCT state is found to equilibrate with the aforementioned states giving a rare three-state equilibrium where the third state is a charge separated state storing ΔG° ≥ 1.9 eV of energy. In order to introduce an aspect of vectorial charge separation into donor-chromophore-acceptor triads, 1,10-phenanthroline ligands bearing bithiophene moieties are introduced as donor ligands into Ru²⁺-based triads with laminate polypyridyl acceptor ligands; dipyrido[3,2-a:2',3'-c]phenazine (dppz), tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine (tpphz), and 9,11,20,22-tetraazatetrapyrido[3,2-a:2',3'-c:3'',2''-l:2''',3''']-pentacene (tatpp). Triads incorporating bithiophene amide diimine ligands and laminate acceptor ligands (50-52) have long-lived charge separated excited states (τes = 2.2 – 7.0 μs), where an electron is localized on the central portion of the acceptor ligand. Charge separated excited states in these triads transiently store an appreciable amount of energy (ΔG° ≈ 0.98 – 1.41 eV)Science, Faculty ofChemistry, Department ofGraduat