Triplet Energy Gap‐Regulated Room Temperature Phosphorescence in Host‐guest Doped Systems

The organic room temperature phosphorescence (RTP) materials via host‐guest doped method receive considerable attention in the fields of optoelectronics, bioimaging, and information encryption. Despite many host‐guest doped materials with excellent RTP properties have been developed, their luminous mechanism is still limited. Here, a series of host‐guest doped materials, using Benzophenone as the host and quinone compounds as the guests, were constructed to investigate the effect of the triplet energy gap (ΔET) between the host and guest on triplet states population. The guest’s triplet state is proposed to be a “triplet energy reservoir”, gathering the triplet excitons to emit RTP when ΔET is large and returning triplet excitons to the host when ΔET is small. By combining the results of steady‐state and delayed emission spectra, time‐resolved transient absorption, and theoretical calculations, A bidirectional energy transfer process is proved, which are triplet‐triplet energy transfer and reverse triplet‐triplet energy transfer processes. The thermal equilibrium of these two energy transfer processes can be regulated by the ΔET and temperature. The potential applications of these RTP properties are also realized in data encryption and anti‐counterfeiting. This work provides valuable insight into the design of host‐guest doped materials based on energy transfer mechanisms.