The Fluorometric Detection of Explosives: An Application of Photoluminiscent Coordination Polymers

Two-dimensional coordination polymers (COPs), a class of metal-organic hybrid polymeric systems are catching the attention of both technologists and researchers due to their ability to exhibit remarkable properties ranging from electrical conductivity to fluorescence arising due to their unique molecular structure and composition. Herein, we report on the synthesis and molecular structural characterization of four different two-dimensional coordination polymers obtained by reacting different metal acetates with 1,2,4,5-benzenetetramine. Their structural characterization was carried out using various spectroscopic and microscopic techniques such as FTIR, UV-vis, Raman, XPS, FESEM, HRTEM, etc., to confirm the two-dimensional layered structure unequivocally. Photophysical studies confirm the exhibition of fluorescence by these COPs with reasonably high quantum yields. All four COPs formed showed the capability to sense different nitroaromatic and non-nitro aromatic systems in the solution phase. Among all the explosives used, trinitrophenol and trinitrotoluene showed very high sensitivity as well as selectivity. The sensitivity was found to be as low as 0.2 mu M. The quenching mechanism was probed with various methods, and it was found to follow static quenching as the predominating quenching process. This selective and sensitive quenching was used to devise a prototype device capable of detecting TNP at very low concentrations visually.