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

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