Unveiling Dexter-Type Triplet–Triplet Energy Transfer of Homologue Room-Temperature Phosphorescence in Host–Guest Doped Systems

Intermolecular energy transfer plays an important role in organic-doped room-temperature phosphorescence (RTP). However, it is difficult to precisely design high-performance RTP by organic-doped systems unless the insight into luminescence is clear. Here, the luminescent mechanism using benzophenone (BP) as host and BP's homologues as guests is investigated by steady-state and delayed photoluminescence, time-resolved transient absorption, and theoretical calculations. A Dexter-type triplet-triplet energy transfer between the host and guest is confirmed. The triplet energy gap (Δ<i>E</i>_T) between host and guest, with values around 0.35 eV, is significant for RTP with high phosphorescence quantum yields and long lifetime. These results pave the way for precise control strategies for luminescent color, lifetime, and quantum yield in homologue-doped RTP.