Photophysical properties of charged cyclometalated Ir(III) complexes: A joint theoretical and experimental study

The photophysical properties of a series of charged biscyclometalated [Ir(ppy)₂(N^{^}N)]¹⁺ complexes, where ppyH is 2-phenylpyridine and N^{^}N is 2,2′-bipyridine (bpy), 6-phenyl-2,2′-bipyridine (pbpy), and 6,6′-diphenyl-2,2′- bipyridine (dpbpy) for complexes 1, 2, and 3, respectively, have been investigated in detail. The photoluminescence performance in solution decreases from 1 to 3 upon attachment of phenyl groups to the ancillary ligand. The absorption spectra recorded over time suggest that complex 3 is less stable compared to complexes 1 and 2 likely due to a nucleophilic-assisted ancillary ligand-exchange reaction. To clarify this behavior, the temperature dependence of the experimental intrinsic deactivation rate constant, k_in = 1/τ, has been investigated from 77 K to room temperature. Temperature-dependent studies show that nonemitting metal-centered (MC) states are accessible at room temperature for complex 3. The experimental results are interpreted with the help of theoretical calculations performed within the density functional theory (DFT) approach. Calculations suggest that attachment of a phenyl group to the ancillary ligand (2) promotes the temperature- independent deactivation pathways, whereas attachment of a second phenyl group (3) also makes the temperature-dependent ones accessible through population of nonradiative ³MC excited states.