Ln(III)-cored complexes based on 2-thenoyltrifluoroacetone 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 Ln3+ ion. Their photophysical studies indicate the sensitization of Ln3+ luminescence by energy transfer through the excited triplet state of β-diketone ligand. Nanosecond (ns) transient absorption behavior of Ln3+-[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 β-diketone ligand to Er3+ ion occurs approximately faster than that of the oxygen quenching rate.