Hydrogen-Bonded Two-Component Ionic Crystals Showing Enhanced Long-Lived Room-Temperature Phosphorescence via TADF-Assisted Forster Resonance Energy Transfer

Molecular room-temperature phosphorescent (RTP) materials with long-lived excited states have attracted widespread attention in the fields of optical imaging, displays, and sensors. However, accessing ultralong RTP systems remains challenging and examples are still limited to date. Herein, a thermally activated delayed fluorescence (TADF)-assisted energy transfer route for the enhancement of persistent luminescence with an RTP lifetime as high as 2 s, which is higher than that of most state-of-the-art RTP materials, is proposed. The energy transfer donor and acceptor species are based on the TADF and RTP molecules, which can be self-assembled into two-component ionic salts via hydrogen-bonding interactions. Both theoretical and experimental studies illustrate the occurrence of effective Forster resonance energy transfer (FRET) between donor and acceptor molecules with an energy transfer efficiency as high as 76%. Moreover, the potential for application of the donor-acceptor cocrystallized materials toward information security and personal identification systems is demonstrated, benefitting from their varied afterglow lifetimes and easy recognition in the darkness. Therefore, the work described in this study not only provides a TADF-assisted FRET strategy toward the construction of ultralong RTP, but also yields hydrogen-bonding-assembled two-component molecular crystals for potential encryption and anti-counterfeiting applications.