A benzylidene-amine scaffold as a colourimetric sensor for picric acid: computational studies and real-time applications using matchstick head powder

A series of simple and cost-effective benzylidene-amine appended probes (E)-4-((4-(allyloxy) benzylidene)amino)-N-phenyl aniline (L-1), (E)-N-phenyl-4-((2,3,4-trimethoxybenzylidene) amino)aniline (L-2), and (E)-4-((2-nitrobenzylidene)amino)-N-phenyl aniline (L-3) have been developed for the rapid detection of picric acid (PA) and explored for the same. Notably, L-3 showed no changes in its UV spectrum or colour upon interaction with PA. In contrast, when PA was added to L-1 and L-2, there were significant changes in absorption, resulting in distinct colour changes. Mole fraction analysis indicated a 1:1 ratio between the probes and PA. The detection limits for PA were impressively low, measuring 4.37 × 10^{- 7} M for L-1 and 4.56 × 10^{- 6} M for L-2. This demonstrates the effectiveness of these probes in detecting PA, even at very low concentrations. Importantly, this work marks the first application of benzylidene-amine probes for the detection of PA. The sensing studies were supported by theoretical analyses and calculations, which confirmed the selective detection of PA using matchstick head powder (MSPS) and a test kit based on paper strips. Additionally, smartphone-assisted detection using an RGB tool was successfully demonstrated.