Luminescent lanthanide complexes with a pyridine-bis(carboxamide)-bithiophene sensitizer showing wavelength-dependent singlet oxygen generation

摘要

A new pyridine-bis(carboxamide)-based ligand with a bithiophene pendant, 2Tcbx, was synthesized. Its lanthanide ion (Ln(III)) complexes, [Ln(2Tcbx)(2)](3+), were isolated and their photophysical properties were explored. Upon excitation at 360 nm, these complexes display emission in the near-infrared (NIR) with efficiencies of 0.69% for Ln(III) = Yb-III, 0.20% for Ln(III) = Nd-III, and 0.01% for Ln(III) = Er-III, respectively. Concurrent O-1(2) formation was seen for all complexes, with efficiencies of 19% for the Yb-III complex, 25% for the Nd-III complex, and 9% for the Er-III complex. When exciting at a longer wavelength, 435 nm, only Ln(III) emission was observed and larger efficiencies of Ln(III)-centered emission were obtained. The lack of O-1(2) generation indicates that energy pathways involving different ligand conformations, which were investigated by transient absorption spectroscopy, are involved in the sensitization process, and enable the wavelength-dependent generation of O-1(2).