A Ni (II) based Fluorescent Coordination Architecture for Selective Sensing of Trinitrophenol (TNP) in an Aqueous Medium.

A Ni (II)-based fluorescent coordination architecture was successfully synthesised using a multifunctional ligand 2-(4-carboxyphenyl)-1 H-benzo[d] imidazole-6-carboxylic acid (L) under solvothermal conditions and characterised using several analytical techniques such as elemental analysis, FTIR spectroscopy, thermogravimetric analysis, and powder X-ray diffraction studies. The synthesised coordination architecture exhibits excellent fluorescent emission in water, attributed to ligand-centred π-π* transitions modulated by metal coordination. Interestingly, this compound demonstrates highly selective and sensitive fluorescence quenching of Trinitrophenol (TNP) among various nitroaromatic explosives, including 4-NT, 2-NT, 2-NP, 3-NP, 4-NP, 1,3-DNB, and 2,4-DNP. A remarkable detection limit of 0.183 ppm was obtained, indicating excellent sensing performance. Density functional theory (DFT) calculations reveal that the sensing mechanism is predominantly ligand-centered and driven by a photo-induced electron transfer (PET) process. The strong electron-accepting character of TNP, together with H-bonding interactions between TNP and 1, promotes efficient electron transfer from the excited ligand to TNP, resulting in significant fluorescence quenching. It also showed rapid response and good stability in aqueous medium, highlighting its potential as an efficient fluorescent probe for trace-level detection of TNP in water.