Intermolecular Interactions and Aggregation of <i>fac</i>-Tris(2-phenylpyridinato‑<i>C</i>²,<i>N</i>)iridium(III) in Nonpolar Solvents

The intermolecular interaction and aggregation of the neutral complex fac-tris­(2-phenylpyridinato-C2,N)­iridium­(III) (fac-Ir­(ppy)3) in solution was investigated. Intermolecular interactions were found to effectively decrease the luminescence lifetime via self-quenching with increasing fac-Ir­(ppy)3 concentrations. A Stern–Volmer plot for quenching in acetonitrile was linear, due to bimolecular self-quenching, but curved in toluene as the result of excimer formation. 1H NMR spectra demonstrated a monomer–aggregate equilibrium which resulted in spectral shifts depending on solvent polarity. X-ray crystallography provided structural information concerning the aggregate, which is based on a tetramer consisting of two Δ-fac-Ir­(ppy)3–Λ-fac-Ir­(ppy)3 pairs. Offset π–π stacking of ppy ligands and electrostatic dipole–dipole interactions between complex molecules play an important role in the formation of these molecular pairs.