A series of heteroleptic bis(tridentate) ruthenium(II) complexes, each bearing a substituted 2,2':6',2 ''-terpyridine (terpy) ligand, is characterized by room temperature microsecond excited-state lifetimes. This observation is a consequence of the strongly sigma-donating and weakly pi-accepting tridentate carbene ligand, 2',6'-bis (1-mesityl-3-m ethyl-1,2,3-triazol-4-yl-5-idene)-pyridine ((CNC)-N-boolean AND-C-boolean AND), adjacent to the terpy maintaining a large separation between the ligand field and metal-to-ligand charge transfer (MLCT) states while also preserving a large (MLCT)-M-3 energy. The observed lifetimes are the highest documented lifetimes for unimolecular ruthenium(II) complexes and are four orders in magnitude higher than that associated with [Ru(terpy)(2)](2+).