Photophysical properties of Re(pbt)(CO)4 studied by high resolution spectroscopy

Photophysical properties of Re(pbt)(CO)4 are investigated at cryogenic temperatures and high magnetic fields. The highly resolved spectra show that the zero field splitting of the lowest triplet T1 into three substates is smaller than 2 cm−1. With this result, the T1 state can be classified as only slightly MLCT-perturbed 3LC (3ππ∗) state. Consistently, spin-lattice relaxation times are slow at T = 1.2 K and emission decay times with τI = 960 μs, τII = 320 μs, and τIII = 24 μs are long due to only small singlet admixtures. The vibrational satellite structures observed reflect different vibrational deactivation mechanisms and reveal similar geometries of the emitting triplet and the ground state.