Enhancement on Visible Light-Induced Cyclization Reactivity of a Diarylethene–Perylenebisimide Dyad by Incorporating Heavy Atom Effect with El-Sayed Rule

A visible light photoswitchable diarylethene–perylenebisimide (DAE–PBI) dyad, incorporating bromine heavy atoms and a ketone linker in the molecular framework, is developed. In order to enhance the visible light-induced cyclization reactivity of a DAE–PBI dyad, in this study, an “internal heavy atom effect” with the “El-Sayed rule” into the molecular design is incorporated. From the theoretical calculation on the contribution ratio of bromine atoms to the molecular orbital (MO) in lowest unoccupied molecular orbitals (LUMOs) and the value of spin–orbit coupling, it is expected that the designed DAE–PBI dyad has high reactivity for visible light-induced cyclization reactions. The synthesized dyad exhibits efficient visible light-induced cyclization reaction not only in heavy atom-containing solvents but also in typical heavy atom-free solvents. These results indicate that the combination of the internal heavy atom effect and the El-Sayed rule effectively contributes to the visible light-induced cyclization reactivity in the dyad. These results will pave the way for new molecular designs to develop UV-free photoswitchable molecules.