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

A new pyridine-bis(carboxamide)-based ligand with a bithiophene pendant, 2Tcbx, was synthesized. Its lanthanide ion (Ln) complexes, [Ln(2Tcbx)], 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 = Yb, 0.20% for Ln = Nd, and 0.01% for Ln = Er, respectively. Concurrent O formation was seen for all complexes, with efficiencies of 19% for the Yb complex, 25% for the Nd complex, and 9% for the Er complex. When exciting at a longer wavelength, 435 nm, only Ln emission was observed and larger efficiencies of Ln-centered emission were obtained. The lack of O 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.