All-Visible (>500 nm)-Light-Induced Diarylethene Photochromism Based on Multiplicity Conversion via Intramolecular Energy Transfer

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 visible-light-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.