Structural and spectroscopic properties of Ir(III) complexes with phenylpyridine ligands: Absorption spectra without and with spin–orbit-coupling

The absorption spectra of [Ir(ppy)3] and [Ir(ppy)2(CO)Cl)] have been calculated by means of TD-DFT methods based on optimized structures, including spin–orbit coupling. Whereas spin–orbit effects modify the spectrum of the tri-substituted phenylpyridine reference complex they do not change significantly the absorption properties of the carbonyl/halide substituted complexes. The absorption spectra have been assigned on the basis of the spin–orbit states and the emissive properties of the complexes have been interprated from the singlet/triplet mixing and spin–orbit splitting of the lowest S1 singlet and T1 triplet states. The theoretical results agree rather well with the experimental data available for this class of complexes, reproduce the zero-field splittings observed for the T1 states at low-temperature and give a new interpretation of the emissive properties. The presence of low-lying mixed XLCT/MLCT states of weak intensities in [Ir(ppy)2(CO)Cl)] limits the spin–orbit effects as compared to [Ir(ppy)3], the spectrum of which is characterized by nearly pure MLCT states in the visible energy domain.