Ruthenium Imidazophenanthrolinium Complexes with Prolonged Excited-State Lifetimes

A series of ruthenium polypyridyl complexes [Ru(tbbpy)3]-[PF6]2 (0, tbbpy = 4,4-di-tert-butyl-2,2-bipyridine), [Ru(tbbpy)2(bbip)][PF6]3 {1, (bbip)Br = 1,3-(bisbenzyl)-1Himidazo[ 4,5-f][1,10]phenanthrolinium bromide}, [Ru(tbbpy)-(bbip)2][PF6]4 (2), and [Ru(bbip)3][PF6]5 (3) were synthesized. The new complexes 2 and 3 were fully characterized, and their X-ray crystal structures, absorption and emission spectra, quantum yields of emission, and cyclic voltammograms were determined. Within this series, a trend towards increased lifetime and quantum yields of emission can be observed, especially in the presence of oxygen. The location of the first excited state on the imidazophenanthrolinium ligands has been elucidated by resonance Raman spectroscopy of 1 and 3, which revealed that the energy of the π* orbitals of the bbip ligands is lower than that of the π* orbitals of the tbbpy ligand.