New photochromic chemosensors for Hg2+ and F−

Two new chemosensors (1a and 1b) based on photochromic dithienylcyclopentene were designed and synthesized, and their spectral behaviors toward various metal ions and anions were investigated in detail. Compounds show excellent optical properties and distinguish Hg2+ and F− in CH3CN. Job’s plot reveals that the presence of Hg2+ induces the formation of a 1:1 complex between 1a or 1b and Hg2+. From the spectral responses and 1H NMR analysis, the deprotonation of the thioamide protons is proposed to explain the sensing mechanism for 1a and 1b toward F−. It is found that 1a and 1b exhibit ring-opening and ring-closing photoisomerization with UV–vis light irradiation. Furthermore, their photochromic properties can be modulated by Hg2+ and F− ions. Moreover, 1a and 1b in photostationary states become promising sensors for Hg2+ and F− with high selectivity.