Bright green luminescent molecular terbium plastic materials derived from 3,5-bis(perfluorobenzyloxy)benzoate

Abstract

Luminescent lanthanide complexes (Eu³⁺ (1) or Tb³⁺ (2)) involving a highly fluorinated aromatic carboxylate, namely, 3,5-bis(perfluorobenzyloxy)benzoic acid which acts as an antenna chromophore and sensitizes the visible emitting lanthanides, have been synthesized and characterized and their photophysical properties investigated. The results demonstrated that the replacement of high-energy C–H vibrations with fluorinated phenyl groups in the 3,5-bis(benzyloxy)benzoate effectively improves the luminescence intensity and lifetimes of lanthanide complexes. It is interesting to note that the designed fluorinated carboxylate is well suited for the sensitization of Tb³⁺ emission (Φ_sen = 52%), thanks to a favorable position of the triplet state of the ligand as investigated in the Gd³⁺ complex. On the other hand, the corresponding Eu³⁺ complex shows weak luminescence efficiency (Φ_sen = 24%) due to poor match of the triplet state of the ligand with the emissive excited states of the metal ion. In the present work, efforts have also been made to isolate luminescent molecular terbium plastic materials by combining the unique optical properties of lanthanides with the mechanical characteristics, thermal stability, flexibility and film-forming tendency of polymers (PMMA). The photoluminescence quantum yields of polymer–lanthanide hybrid materials are significantly enhanced (53–65%) as compared to that of the Tb³⁺–3,5-bis(perfluorobenzyloxy)benzoate complex.