Ruthenium(II) complexes of 2-aryl-1,10-phenanthrolines: Synthesis, structure, and photophysical properties

The synthesis, characterization, and photochemical investigation of a serie s of Ru(II) complexes having 2-phenyl-and 2,9-diphenyl substituted phenanth roline ligands are reported. Structural characterization of some of the com plexes revealed that the phenyl substituents of the phenanthroline ligand a re oriented nearly perpendicular to the phenanthroline ring and pi-stack wi th adjacent coordinated 2,2'-bipyridyl ligands, Most of the complexes are n onluminescent at room temperature, and temperature-dependent luminescence s tudies suggest nonradiative relaxation in solution is dominated by rapid th ermally activated internal conversion from the initially populated (MLCT)-M -3 state to a ligand field (LF) state which decays rapidly to the ground st ate. The photochemical lability of the complexes was investigated, and it w as found that, while the complexes efficiently populate the substitutionall y labile LF state, yields for ligand loss are less than expected on the bas is of comparison to closely related complexes lacking the phenyl groups whi ch are capable of pi-stacking interactions.