Building bridges through dynamic coupling for organic phosphorescence.

Achieving long-lived room temperature phosphorescence (RTP) in organic materials has garnered significant attention in the field of optoelectronics. Although many host-guest systems with versatile performances have been developed, their photophysical mechanisms remain unclear due to the complicated intermolecular interactions and multiple energy transfer pathways, leading to unavoidable trial-and-error in molecular designs. Here we reveal that the dynamic coupling process in the excited state is crucial for inducing phosphorescence, where host and guest molecules firstly couple to enhance the intersystem crossing efficiency, and then decouple to transfer excitons to the triplet state of guest. Such a process shows universal applicability and tunable performance, with the longest lifetime for red RTP (τ = 2.4 s) reported so far. We anticipate the present work as a starting point for more sophisticated models on excited-state dynamic behaviors within host-guest systems.