An excellent colorimetric and “turn off” fluorescent probe for tetrahydrofuran based on a luminescent macrocyclic samarium(iii) complex

Abstract

In this paper we report a novel probe based on a luminescent 23-membered [1 + 1] Schiff-base macrocyclic mononuclear Sm(III) complex Sm-2_e, originating from the dialdehyde H₂Q_e and 1,2-bis(2-aminoethoxy)ethane precursors, which is synthesized by the Sm(III) ion template method. X-ray structural analyses confirm that each ten-coordinate Sm(III) center with the coordination geometry of a distorted bicapped square antiprism is fully encapsulated by a flexible macrocyclic ligand H₂L2_e to form a “lasso-type” architecture, and this architecture could enable efficient energy transfer in various solvents confirmed by long lifetimes (33.5–65.2 μs) and high quantum yields (0.23–0.76%) of the Sm(III) ion. Simultaneously, complex Sm-2_e could serve as a probe for sensing organic solvents. Particularly, this complex probe Sm-2_e exhibits a highly selective, rapid and sensitive response to tetrahydrofuran (THF), which is easily distinguished by a large absorption shift, even visible to the naked eye, and complete fluorescence quenching. Moreover, the limit of detection for THF is about 0.20% determined by titration experiments, and good selectivity for THF could still be realized in mixture solvents. Consequently, this colorimetric and “turn off” fluorescent probe Sm-2_e could be a valuable candidate as a sensor material for sensing THF which has been rarely reported.