A simple fluorescent switch with four states based on benzothiazole-spiropyran for reversible multicolor displays and anti-counterfeiting

A fluorescent molecular switch (SP-OX-HBT), designed by fusing spiropyran with 2-(2-hydroxyphenyl)benzothiazole (HBT), exhibited red, orange and dark emission color switching among four states in the solution and solid states. The transformation from merocyanine (SP-OX-HBT) to ring-closed spiropyran (SP-HBT-C) or deprotonated ring-closed spiropyran (SP-HBT-CN) could be controlled by visible light or base stimuli, respectively, and these processes are verified by UV-vis spectra. The deprotonated merocyanine form (MC-N) was briefly involved in the basochromic process in solution but stable in the solid state. Besides the significant visible and fluorescent color variations, the single molecular switch has been further successfully applied to construct reversible multicolor displays and for anti-counterfeiting.