Photoswitching molecules that reversibly switch upon visible-light irradiation are some of the most attractive targets for biological and imaging applications. In this study, we found a diarylethene (DAE) derivative having a covalently attached perylenebisimide (PBI) unit (DAE-PBI dyad) underwent an unexpected cyclization reaction upon irradiation with green (500−550 nm) light, where the DAE unit has no absorbance. The photoreactivity was enhanced in solvents containing heavy atoms and in the presence of oxygen. As inferred from the solvent dependence and the calculated excited-state energies of DAE and PBI units, it was suggested that the probable mechanism for this unique visiblelight-induced cyclization reaction is multiplicity conversion based on intramolecular energy transfer from the excited singlet state of the PBI unit to the triplet state of DAE units (i.e., DAE-1 [PBI]* → 3 [DAE]*-PBI). Such a unique photoreaction mechanism with the assistance of oxygen will pave the way for new molecular design for the development of visible-light switching molecules.

Recently, we found a unique visible light-induced photocyclization reaction in a diarylethene-perylenebisimide dyad based on multiplicity conversion via intramolecular energy transfer. Here we report on the remarkable enhancement of photocyclization quantum yield under visible light irradiation by changing the spacer unit from an ester to a ketone group. This simple modification lifts the restrictions of solvent choice and oxygen quenching.