The efficient sensitization of Sm(III) ion by a macrocycle with the matched cavity and energy level

Abstract

A series of mononuclear lanthanide(III) coordination compounds Ln-1a with the “lasso-type” protection have been synthesized based on the flexible [1+1] pendant-arm Schiff-base macrocyclic ligand H2L1a. X-ray structure analysis reveals that the central ten-coordinate Ln(III) ion in every compound adopts distorted bicapped square antiprism geometry which is surrounded by one macrocycle and two axial chelating nitrates. Photophysical measurements have demonstrated that the macrocyclic ligand can serve as an effective sensitizer for Sm(III) ion. The relative compound Sm-1a shows efficient luminescence. Especially, the quantum yields are as high as about 1.48 ± 0.03 and 0.24 ± 0.02% for Sm(III) ion in solid state and methanol, respectively. The fluorescence lifetime is 42.3 μs in solid state together with 24.5 μs in methanol. It is proposed that the macrocyclic ligand plays an important role in guaranteeing the effective match of energy levels for Sm(III) central ion and constructing unique cavity microenvironment to shield the Sm(III) ion emitter from possible quenching effects.