Synthesis of Bis-Thioacid Derivatives of Diarylethene\nand Their Photochromic Properties

Diarylethenes (DAEs)\nare an important class of photoswitchable\ncompounds that typically undergo reversible photochemical conversions\nbetween the open and closed cyclized forms upon treatment with UV\nlight or visible light. In this study, we introduced thioacid functional\ngroups to several photochromic dithienylethene (DTE) derivatives and\nestablished a method that can be used to prepare these photoswitchable\nthioacids. Four thioacid-functionalized diarylethene derivatives were\nsynthesized through the activation of carboxylic acids with <i>N</i>-hydroxysuccinimide, followed by reactions with sodium\nhydrosulfide with yields over 90%. These derivatives exhibited reversible\nphotoswitching and photochromic properties upon treatment with ultraviolet\n(UV) and visible lights. The thioacid groups on these compounds can\nact as reaction sites for attaching other desirable functionalities.\nThe photochromic properties of these new derivatives were characterized\nby using ultraviolet–visible (UV–vis) spectroscopy.\nThe photocyclizations of one of the derivatives and its potassium\nsalt were also characterized by using nuclear magnetic resonance (NMR)\nspectroscopy. The anions of the thioacid formed water-soluble photochromic\nsystems, and their applications as colorimetric sensors in agarose\nhydrogels were demonstrated.