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

Abstract

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.