Mixed-Bridging 2D Luminescent Coordination Polymer: Structure, Selective Sensing of Pollutants in Water, and Fabrication of Photoresponsive Electronic Device

Pyrazine (tppz) and 5-sulfosalicylic acid (H3SSA) mixed-bridging Cd(II)-CP, {[Cd2(HSSA)2(tppz)2]}n (1), is highly luminescent, and the emission has been quenched selectively by Al3+ in the presence of other cations, with a limit of detection (LOD) of 43.9 nM (1.18 ppb). The emission of 1 is also quenched by 4-nitroaniline (4-NA) (LOD, 49 nM) and dicloran (2,6-dichloro-4-nitroaniline, DCN), a pesticide (LOD, 42.8 nM), in an aqueous medium in the existence of 11 other nitroaromatic compounds (NACs). The structure of the probe, 1, shows the diverse bridging by pyridyl-N of tppz and carboxylate-O of HSSA2– to architect a 2D CP with a 16-member metallo-macrocycle, followed by S═O···Cd(II) (2.291(2) Å), π···π (3.892 Å), and C–H···π noncovalent interactions to form a 3D supramolecular structure and cavity. The phenolic–OH of HSSA2– remains uncoordinated in the cavity network. Upon interaction of Al3+/4-NA/DCN with Cd(II)-CP (1), the free phenolic–OH may induce easy dissociation, which may assist in energy transfer for quenching. The interaction has been explained through various experiments and theoretical calculations. The DFT computation determines the band gap as 3.42 eV (experimentally, 3.18 eV), which is motivated to measure the electrical conductivity. The conductivity, 3.53 × 10–5 S m–1 (dark), has been enhanced upon light irradiation to 7.66 × 10–5 S m–1.