New photochromic indoline spiropyrans containing cationic substituent in the 2H-chromene moiety

Abstract

New indoline spiropyrans containing conjugated cationic fragments and bulky substituents in the 2H-chromene moiety were synthesized by a simple one-pot method. The structures of the obtained compounds were confirmed by 1H and 13C NMR (including 2D methods) and IR spectroscopy, as well as by element analysis and HRMS. Molecular structure of 1,3,3-trimethyl-6′-formyl-8′-benzyl-spiro[indoline-2,2′-2H-chromene] was refined by single crystal X-ray. A comparative analysis of the spectral and photochromic properties of salt spiropyrans and similar structures without a cationic fragment was carried out. It was found that the introduction of the cationic substituent at the 6′-position of the 2H-chromene moiety leads to a significant increase in the photoinduced isomer's lifetime