Design of low-energy absorbing and emitting transition metal complexes as potential bioimaging reagents

Abstract

Two novel phosphorescent cyclometalated iridium(III) polypyridine complexes [Ir(dbp)2(N^N)](PF₆) (Hdbp = dibenzo[a,i]phenazine; N^N = ethylenediamine (en) (1), 4,7-diphenyl-1,10-phenanthroline (Ph₂-phen) (2)) were synthesized and characterized. Their electronic absorption and photophysical properties were studied. Upon photoexcitation, both complexes displayed intense and long-lived yellow emission in fluid solutions at 298 K. The emission of both complexes 1 and 2 was assigned to a triplet metal-to-ligand charge-transfer (³MLCT) (dπ(Ir) → π*(dbp)) excited state. The intracellular localization properties of the complexes were also examined by laser-scanning confocal microscopy. Both complexes were efficiently internalized into HeLa cells.