A substituted benzothiazolinic merocyanine derivative as a reversible, selective, colorimetric and fluorescent probe for HSO4− in aqueous solution

Abstract

A benzothiazolinic bromide salt of merocyanine form of spiropyran has been synthesized through a coupling reaction between a (3-(2-carboxyethyl)benzo[d]thiazol-3-ium) bromide and 2‑hydroxy-1-naphthaldehyde. The structure of the salt was examined using IR, NMR, and HR-MS techniques. Due to the zwitterionic nature and H-bond formation ability of the product, its affinity towards toxic anions was investigated in 50% aq. MeCN at pH 7.4. The zwitterionic benzothiazolinic bromide salt selectively detected the presence of HSO4−ion in the solution by showing a color change from purple to yellow and displayed a spectral change (hypsochromic shift) in both absorption and fluorescence spectra. The dynamic light scattering and scanning electron microscope studies were utilized to study the aggregation of the merocyanine salt. Moreover, the aggregation was observed to be controlled by light. The 1H NMR studies confirmed the displacement of bromide by HSO4− ion. The computational studies provided details of the complex and conformation stability at the molecular level. To explain the observed absorption spectra further, electronic excitation parameters were calculated using time-dependent density functional theory (TD-DFT).