Electrochemical and spectroscopic properties of cyclometallated and non-cyclometallated ruthenium(II) complexes containing sterically hindering ligands of the phenanthroline and terpyridine families

Two series of cyclometallated and noncyclometallated ruthenium(II) complexes incorporating mono- or disubstituted 1,10-phenanthroline- and 2,2':6',2' `-terpyridine-type Ligands have been synthesized and characterized. An X-ray crystal structure for one of the complexes, Ru(ttpy)(mapH)(Cl)(PF6), has been obtained (mapH = 2-p-anisyl-1,10-phenanthroline; ttpy = 4'-tolyl-2,2':6',2''-terpyridine). Distinct electrochemical and photophysical properties have been observed for the two series: a remarkable feature is the observation of relatively long-lived MLCT excited states (from 70 to 106 ns at room temperature in CH3CN) for three of the cyclometallated complexes. A discussion is given on the role of factors like sigma donation by the cyclometallating Ligands, interligand steric hindrance and interligand pi-pi interactions that affect the electrochemical and spectroscopic properties.