Spectroscopy and Photophysics in Cyclometalated RuII-Bis(bipyridyl) Complexes

A series of cyclometalated RuII coordination compounds of the general structural formula [Ru(bpy)2(C boolean AND N)]PF6 {C boolean AND N = 2-phenylpyridine (1), 2-(2,4-difluorophenyl)pyridine (2), 2-(4-methoxyphenyl)-5-methylpyridine (3), benzo[h]quinoline (4); bpy = 2,2'-bipyridine} have been synthesized, structurally and electrochemically characterized, and examined by using a battery of spectroscopic techniques. The combination of static and dynamic photoluminescence at room temperature and 77 K, resonance Raman spectroscopy, cyclic voltammetry, spectroelectrochemistry, and ultrafast transient absorption spectroscopy reveal that although the nature of the cyclometalating ligand substantially affects the oxidation potential at the metal center the lowest-energy metal-to-ligand charge-transfer excited state always retains pure Ru?bpy character across this series of molecules, and the cyclometalating subunit plays the role of ancillary ligand.