Structure-property relationship studies of photoactive tridentate ligands and their applications in sensing of Cu(II) and Fe(II) ions

Abstract

A series of tridentate polypyridyl N^N^N/N^C^N-coordinating ligands (R1, R2, L1, L2) were synthesized by palladium-catalyzed Suzuki-Miyaura C–C bond-forming and N-methylation reactions in good-to-excellent yields (70–97%). These ligands were characterized by a set of analytical techniques including NMR, HRMS and single-crystal XRD. The electrochemical and photophysical properties of these ligands were examined using cyclic voltammetry, UV–vis absorption and luminescence spectroscopies. Theoretical calculations at the level of DFT and TD-DFT were also performed for the detailed studies of the optoelectronic properties of these compounds. These ligands displayed either an admixture of singlet ligand-centered (1LC) and singlet charge-transfer (1CT) transitions or pure 1LC/1CT luminescence in some cases. Ligands (L3 and L4) which are charged in nature were further used as selective chemosensors for the detection of Cu(II) and Fe(II) ions with a “turn-off” fluorescence behavior in a binding stoichiometry of 2:1 = ligand:M(II) [M = Fe(II)/Cu(II)] and a limit of detection up to 4.66–21.71 ppm level. © 2023 Elsevier B.V.