Reversible Photoswitching between Fluorescence and Room Temperature Phosphorescence by Manipulating Excited State Dynamics in Molecular Aggregates

Regulation of fluorescence-phosphorescence pathways in organic molecular aggregate remains a challenge due to the complicated singlet-triplet excited state dynamics process. Herein, we demonstrated a successful example (o-BFT) to realize photoreversible fluorescence and room temperature phosphorescence (RTP) switching based on an effective strategy of integrating a phosphor (dibenzofuran) with a photoswitch (dithienylbenzothiophene). o-BFT exhibited dual emission of fluorescence and RTP in both powder and doping polymer film. Notably, the long-lived RTP of o-BFT could be repeatedly erased and restored through reversible photocyclization and decyclization under alternate ultraviolet and visible photoirradiation. In-depth theoretical and spectroscopic investigations revealed that the triplet inactivation was dominated by a photo-controlled triplet-to-singlet Förster resonance energy transfer from light-activated o-BFT to photoisomer c-BFT. Yet, the initial fluorescence could be preserved in this process to afford a photoreversible fluorescence-RTP switching.