Novel 2-Arylbenzothiazoles: Selective Chromogenic and Fluorescent Probes for the Detection of Picric Acid

A series of 2-arylbenzothiazoles has been designed and synthesized as chromogenic and fluorescent probes for the detection of picric acid (PA) over other nitro analytes. A straightforward condensation of a variety of aryl nitriles with 2-aminobenzenethiol under metal- and base-free conditions afforded the corresponding products in 26-98% yields. All 2-arylbenzothiazoles could efficiently sense PA at micromolar levels. The highly sensitive compound 2-(4-((2-methyl-1H-imidazol-1-yl)methyl)phenyl)benzo[d]thiazole (3c) showed 95% fluorescence quenching on addition of 1.0 eq of PA which can be attributed to hydrogen bonding and ground state charge transfer complex formation with a detection limit of 19.0 M. The high sensitivity of 3c for PA detection was also established by test strips experiment. The sensing mechanism was explored by (HNMR)-H-1 titrations and Job's plot.