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

摘要

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 S_1 singlet and T_1 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 T_1 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.