Short-Range Coulomb Interaction Is a Key to Switch the Utilization of Higher Triplet Excitons in Multiresonance Thermally Activated Delayed Fluorescence Doped Film

Multiresonance thermally activated delayed fluorescence (MR-TADF) materials have attracted widespread attention due to ultrahigh definition display standards. However, many MR-TADF materials lack TADF properties in both the solution and solid states. Interestingly, the TADF characteristics appear once these MR-TADF compounds are doped in a suitable host film, but the precise mechanism involved in the host–guest interaction remains uncertain. Herein, we systematically investigated the role of host–guest interactions employing doped films (DABNA-1@mCBP and DABNA-1@DPEPO) with opposite phenomena. The results indicate that mCBP with a V-shape and enhanced rigidity could facilitate the formation of an energy spacing layer by employing short-range Coulomb energy through the MR luminescent core, which could offset the sensitivity of the stacking distance, enhancing the coupling between T₁ and T₂, and thus switch the reverse internal conversion and the higher T₂ reverse intersystem crossing process. This work is a further development of luminescence mechanisms and an update of the host–guest interaction criteria for the targeted design of doped films.