Aggregation-Induced Emission from Fluorophore–Quencher Dyads with Long-Lived Luminescence

Aggregation-induced emission (AIE)
is an important photophysical
phenomenon in molecular materials and has found broad applications
in optoelectronics, bioimaging, and chemosensing. Currently, the majority
of reported AIE-active molecules are based on either propeller-shaped
rotamers or donor–acceptor molecules with strong intramolecular
charge-transfer states. Here, we report a new design motif, where
a fluorophore is covalently tethered to a quencher, to expand the
scope of AIE-active materials. The fluorophore–quencher dyad
(FQD) is nonemissive in solutions due to photoinduced electron-transfer
quenching but becomes luminescent in the solid state. The intrinsic
emission lifetimes are found to be within the microseconds domain
at both room and low temperatures. We performed single-crystal X-ray
diffraction measurement for each of the FQDs as well as theoretical
calculations to account for the possible origin of the long-lived
AIE. These FQDs represent a new class of AIE-active molecules with
potential applications in organic optoelectronics.