Ln(III)-cored complexes based on 2-thenoyltrifluoro acetone ligand for near infrared emission: Energy transfer pathway and transient absorption behavior

Lanthanide(III)-cored complexes based on 2-thenoyltrifluoroacetone (TTA) ligand for near infrared (NIR) emission have been developed to investigate the energy transfer pathway from the antenna ligand to the Ln(3+) ion. Their photophysical studies indicate the sensitization of Ln(3+) luminescence by energy transfer through the excited triplet state of beta-diketone ligand. Nanosecond (ns) transient absorption behavior of Ln(3+)-[TTA](3)(terpy) complexes at room temperature is explored. The triplet-triplet absorption spectrum for Gd3+ -[TTA](3)(terpy) is observed under degassed condition, whereas it is hardly observed in Er3+ -[TTA](3)(terpy) complex. The sensitizing process in Er3+-[TTA](3)(terpy), through the triplet state of TTA ligand to Er3+ ion, is also independent on the presence of oxygen. It indicates that the energy transfer rate through the excited triplet state of beta-diketone ligand to Er3+ ion occurs approximately faster than that of the oxygen quenching rate. (C) 2007 Elsevier B.V. All rights reserved.