The impact of bromine substitution on the photophysical properties of a homodinuclear Ru–tpphz–Ru complex

Ruthenium–polypyridine complexes play an important role as photosensitizers in supramolecular photocatalysis. Using multiple Ru-centers within a single supramolecular catalyst might be a promising path for improving its efficiency. The connection of several chromophores may, however, lead to direct interaction amongst individual photoactive centers, which is at the core of the work at hand. The work focuses on the photophysics of [(tbbpy)2Ru(3,16-Br2-tpphz)Ru(tbbpy)2](PF6)4 (1, tpphz = tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2″′,3″′-j]phenazine, tbbpy = 4,4′-di-tert.-butyl-2,2′-bipyridine) and aims at detailing the impact of the bromine substituents on bridging ligand photoinduced intramolecular charge-transfer dynamics. It is shown that the introduction of the bromine reduces the driving force for intra-ligand charge-transfer steps and impacts exciton–exciton annihilation at high pump intensities.