Wavelength-Dependent Singlet Oxygen Generation in Luminescent Lanthanide Complexes with a Pyridine-Bis(Carboxamide)-Terthiophene Sensitizer

Lanthanide ion (Ln^III ) complexes, [Ln(3Tcbx)₂ ]³⁺ (Ln^III =Yb^III , Nd^III , Er^III ) are isolated with a new pyridine-bis(carboxamide)-based ligand with a 2,2':5',2''-terthiophene pendant (3TCbx), and their resulting photophysical properties are explored. Upon excitation of the complexes at 490 nm, only Ln^III emission is observed with efficiencies of 0.29 % at 976 nm for Ln^III =Yb^III and 0.16 % at 1053 nm for Ln^III =Nd^III . Er^III emission is observed but weak. Upon excitation at 400 nm, concurrent ¹ O₂ formation is seen, with efficiencies of 11 % for the Yb^III and Nd^III complexes and 13 % for the Er^III complex. Owing to the concurrent generation of ¹ O₂ , as expected, the efficiency of metal-centered emission decreases to 0.02 % for Yb^III and 0.05 % for Nd^III . The ability to control ¹ O₂ generation through the excitation wavelength indicates that the incorporation of 2,2':5',2''-terthiophene results in access to multiple sensitization pathways. These energy pathways are unraveled through transient absorption spectroscopy.