Structural Elucidation of the 1D Cd(II) Coordination Polymer and Its Application in the Selective Detection of TNP and the Schottky Diode Device Fabrication

Abstract

Research on the application of photoluminescence activity in the sensing of ions/molecules and the conductive nature of coordination polymers has attracted attention in recent years as an objective for Sustainable Development Goals. In this context, we designed and synthesized a one-dimensional (1D) coordination polymer {[Cd₂(tppz)(2-ATPA)₂(H₂O)₂]·(MeOH)₂}_n (CP1), bridged by 2,3,5,6-tetrakis(2-pyridyl)-pyrazine (tppz) and 2-amino terephthalic acid (H₂ATPA) to the Cd²⁺ center. Amine (–NH₂) and one of the carboxylate (–COO^–) groups from H₂ATPA bridged two adjacent Cd(II) centers, forming a 14-member metalla-macrocycle that propagates in a one-dimensional (1D) pattern. The overall charge of the coordination unit was balanced by that of the other free carboxylates (–COO^–) of the acid linker. The H-bonding between amine (–NH₂) and carboxylate (–COO^–) groups of the neighboring coordinating unit architects the supramolecular frameworks. Hirshfeld surface analysis also computed the incidence of various types of noncovalent interactions (C···C; Cd···N; Cd···H; H···H; C···N; C···O; N···O; O···O). The CP1 in the dispersed phase displayed strong blue emission at 428 nm in an acetonitrile medium, which was quenched selectively by 2,4,6-trinitrophenol (TNP) without interference in the presence of 12 other nitroaromatic compounds (NACs). The estimated limit of detection (LOD) value was as low as 0.096 ppm (0.18 μM). The interaction between CP1 and TNP was supported by the lifetime of the excited state of the composite (CP1+TNP) (8.17 ns), which is significantly higher than that of CP1 (2.54 ns). This primarily confirmed the stability of the composite at the excited state (CP1*+TNP). Thus, the longer lifetime of the composite substantiated the possibility of dynamic quenching. Tauc’s plot using the absorption spectrum estimated an optical band gap of 4.11 eV (DFT computed, 3.86 eV), which implies the semiconducting nature of the material. The electrical conductivity was measured using an ITO/CP1/Al electrode, which determined the electrical conductivity of 3.76 × 10^–6 S m^–1 in the dark phase and increased to 6.01 × 10^–6 S m^–1 upon light irradiation. This result validated the photoresponsive device applications.