Nature of Anti-Dissipative High-Energy Excited States in Quaterpyridine-Bridged Ruthenium Complexes

High-energy excited states with slow rates for internal conversion to the lowest-energy excited state are prone to be intercepted before they dissipate energy to the medium. In a previous report, oligomeric Ru(II) photosensitizers bearing a bridging 2,2′:5′,3″:6″,2^‴–quaterpyridine scaffold showed promising anti-dissipative behavior in photoinduced electron transfer reactivity. In here, a range of electron accepting and electron donating substituents were incorporated on the ancillary 2,2′-bipyridine ligands to modulate the excited-state dynamics. This allowed to unambiguously identify the nature of high-energy excited states and derive design guidelines for the achievement of anti-dissipative behavior in oligomeric Ru(II) polypyridines relevant for solar fuels production and photoredox catalysis.