Accessing a Long-Lived ³LC State in a Ruthenium(II) Phenanthroline Complex with Appended Aromatic Groups

The photophysical properties of a series of heteroleptic Ru(II) complexes of the form [Ru(phen)₂(phen-5,6-R₂)]²⁺, where phen = 1,10-phenanthroline and R = phenyl (Ph), p-tert-butylbenzene (p-Ph-tBu), p-methoxybenzene (p-Ph-OMe), and 2-naphthalene (2-naph), have been measured. Variation of the R group does not greatly perturb the electronic properties of the ground state, which were explored with electronic absorption and resonance Raman spectroscopy and are akin to those of the archetypal parent complex [Ru(phen)₃]²⁺. All complexes were shown to possess emissive ³MLCT states, characterized through transient absorption and emission spectroscopy. However, an additional, long-lived excited state was observed in the Ru(II) naphthalene complex. The naphthalene substituents facilitate population of a 40 μs dark state which decays independently to that of the emissive ³MLCT state. This state was characterized as ³LC in nature, delocalized over the naphthalene substituted ligand.