Mechanisms of energy transfer luminescence of lanthanide complexes: A time-dependent density functional theory study

The mechanism of the intra-molecular energy transfer process in trivalent lanthanide- 5-suffosalicylate complexes, which induces long-lifetime luminescence, were investigated by time-dependent density functional theory (TDDFT) calculations. Calculated results of Tb(III) complex showed that square electron is excited with high-frequency to a molecular orbital mixing square* orbital of the ligand and 4f orbitals of Tb. In contrast, no mixed orbitals was found in calculated excited states of Eu complex. These results clearly indicate that the transition to the mixing molecular orbital of square* and 4f orbitals causes the energy transfer luminescence process. The present work showed that TDDFT is a powerful tool for the design of highly emissive lanthanide complexes.