Solvent dependent photoswitching and emission of diarylethenes with a π-conjugated push-pull system

Introduction of push-pull system between carbonyl and dimethylamino groups in the ethene bridge of diarylethene provides access to multifunctional fluorescent switches, responsible for various stimuli (UV and visible light, solvent polarity, and pH change). In this work a thorough study of luminescent and photochromic properties of three cyclopentenone-based derivatives in various solvents was performed. Quantum yields of luminescence as well as forward and backward photochemical reactions were measured, and the kinetic properties of the luminescence decay were determined. The ICT (intramolecular charge transfer) excited state is responsible for the emissive properties, which determines the strong dependence of the emissive properties vs. solvent polarity. Kinetic behavior of the luminescence and its dependence of solvent polarity were explained by the model based on the equilibrium between two isomers of the DAEs open form (parallel, P, and anti-parallel, AP). Dialkylaminobenzylidene moiety, conjugated with cyclopentenone bridge, provides unique combination of bidirectional manipulation by visible light only and complex switching behavior, presumably associated with competitive processes of 6 pi-electrocyclization and E-/Z-isomerization.