Ruthenium(II) Complexes of 2-Aryl-1,10-phenanthrolines: Synthesis, Structure, and Photophysical Properties

The synthesis, characterization, and photochemical investigation of a series of Ru(II) complexes having 2-phenyl- and 2,9-diphenyl substituted phenanthroline ligands are reported. Structural characterization of some of the complexes revealed that the phenyl substituents of the phenanthroline ligand are oriented nearly perpendicular to the phenanthroline ring and pi-stack with adjacent coordinated 2,2'-bipyridyl ligands. Most of the complexes are nonluminescent at room temperature, and temperature-dependent luminescence studies suggest nonradiative relaxation in solution is dominated by rapid thermally activated internal conversion from the initially populated (3)MLCT state to a ligand field (LF) state which decays rapidly to the ground state. The photochemical lability of the complexes was investigated, and it was found that, while the complexes efficiently populate the substitutionally labile LF state, yields for ligand loss are less than expected on the basis of comparison to closely related complexes lacking the phenyl groups which are capable of pi-stacking interactions.