Theoretical study on the kinetic control mechanism of ESIPT for the photocyclization of diarylethylethene derivatives

Multifunctional photochromic diarylethylethene derivatives have attracted much attention from researchers due to their unique physicochemical properties originated from photocyclization. Yu et al. synthesized a terthiazolebased diarylethenes (ap-P) featuring intramolecular hydrogen bonds in experiment. They supposed that there was a competitive relationship between photocyclization and excited-state intramolecular proton transfer (ESIPT). To gain deeply insight into the connection between two reactions, the geometry optimization, the calculation of electron spectra, and the construction of minimum energy paths of ESIPT and cyclization were carried out under solvent and gas phases. These studied were based on closed shell and unrestricted open shell density functional theory, as well as other quantum chemistry methods. Moreover, qualitative and quantitative analyses of the electron structure revealed that the competition between two reactions is fundamentally driven by changes in aromaticity and electron delocalization. Furthermore, it was theoretically proved that the regulation of ESIPT is realized by changing environmental parameters, leading to a novel method for precise control of photocyclization reaction. It is expected to provide theoretical guidance and prediction for the flexible application of multifunctional photochromic molecular switches in photoelectric materials, biomedicine and other fields.