Theoretical study on the photocyclization reactivity mechanism in a diarylethene derivative with multicolour fluorescence modulation

Abstract For a photochromic spiro-diarylethene derivative (Spiro-DAE), its photocyclization reaction and multicolour fluorescence modulation performances were investigated based on a series of density functionals calculations in this work. Some elementary properties such as geometric and electronic structures at ground and the first excited state (S1), absorption and emission spectra in respective open-ring and closed-ring structures were compared, which indicate the cyclization reaction may occur at S1. It is further verified by the lower activation barrier (3.4 kcal/mol) of the transition state at S1 potential energy surface. The photochromic reaction rates for both cyclization and cycloreversion processes were quantitatively estimated, which suggests the much smaller radiative and internal conversion rates contribute to the higher photocyclization rate and thus efficiency. Furthermore, we suspect that the dihydroacridine fragment may make important contribution to the cyclization reaction occurring at S1 considering its contribution to electronic structure.