Excited-state distortions of cyclometalated Ir(III) complexes determined from the vibronic structure in luminescence spectra

The luminescence spectra of [tpy)₂Ir(CN-t-Bu) ₂](CF₃SO₃) in methylcyclohexane glass and frozen n-nonane at 15 K reveal well-resolved vibronic fine structure. The vibronic peaks are assigned by comparison with the vibrational frequencies obtained from Raman and IR spectra and those obtained using DFT electronic structure calculations. The magnitudes of the distortions along the normal coordinates are calculated by fitting the emission spectra using the time-dependent theory of spectroscopy. Broadening effects and the MIME frequency observed at room temperature are interpreted. The most highly distorted normal modes involve atomic motions on the tpy ligand, consistent with the metal to ligand/ligand centered assignment of the electronic transition.