Polyphenylcyclopentadienyl ligands as an effective light-harvestig π-bonded antenna for lanthanide +3 ions
A new approach to design “antenna-ligands” to enhance the photoluminescence of lanthanide coordination compounds based on π-type ligand - polyphenylsubstituted cyclopentadienyl has been developed. The complexes of di-, tri- and tetraphenyl cyclopentadienyl ligands with Tb and Gd has been synthesized and all the possible structural types from mononuclear to di- and tetranuclear as well as coordination polymer were obtained. All types of the complexes have been studied by single-crystal X-ray diffraction and optical spectroscopy. All complexes are luminescent at ambient temperature and two of them have relatively high quantum yields (50 and 60%). Analysis of energy transfer process has been performed and supported by quantum chemical calculations. The role of a low-lying intraligand charge transfer state formed by extra coordination with K+ in the Tb+3 ion luminescence sensitization is discussed. New aspects for design of lanthanide complexes containing π-type ligands with desired luminescence properties have been proposed.