Although chemical structural modification of naphthalimides is widely employed for the purpose of sensing explosives, the effects of such modification have been little explored. Herein, we report the design and synthesis of a new naphthalimide-benzothiazole conjugate (1) and its ability to sense various nitrophenols by means of its colorimetric and fluorescent characteristics. Under long-range UV light (365 nm), 1 displayed a color change of its solution from bluish to colorless only upon addition of 2,4,6-trinitrophenol (TNP). Photoluminescence spectroscopy showed quantitative fluorescence quenching by TNP of the emission peaks of 1 at 398 nm and 418 nm due to donor–acceptor electron transfer. The interaction of 1 with TNP was via a cooperative, non-covalent hydrogen-bonding interaction. Receptor 1 exhibited high sensitivity and selectivity towards TNP over various aromatic nitro analytes. The binding constant (K) and Stern–Volmer constant (Ksv) between 1 and TNP were found to be 5.332 × 10−5 M and 2.271 × 106 M−1, respectively. Furthermore, the limit of detection was calculated and found to be as low as 1.613 × 10−10 M.
We report synthesis of (2E,4E)-2-(benzo [d]thiazol-2-yl)-4-(1,3,3trim ethylindolin-2-ylidene) but-2-enenitrile (MC-BTH-1) chromophore and employed for picric acid sensing. MC-BTH-1 was prepared by Knoevenagel condensation of 2-(benzo[d]thiazol-2-yl) acetonitrile and (Z)-2-(1,3,3-trimethylindolin-2-ylidene) acetaldehyde in the presence of catalytic amount of piperidine in dry ethanol. The MC-BTH-1 conjugate displayed a remarkable sensing property towards picric acid in presence of interfering nitroaromatic compounds. The sensing of nitroaromatic compounds was investigated by means of UV-vis absorption, fluorescence and 1 H NMR spectroscopic. Furthermore, colorimetric visualization of receptor MC-BTH-1 with the addition of various analytes under 365 nm UV light shows only color change from green to dark green for 2,4,6-trinitrophenol (TNP) and no significant color change was observed for other analytes. Under optimized condition the detection limit towards TNP and 2,4-dinitrophenol (DNP) are 1.58 × 10 À 9 M and 1.48 × 10 À 9 M, respectively. These results clearly show high sensitivity of system at low concentration with fluorescence quenching quantum efficiency ∼ 88%.
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