Tuning Hybridized Local and Charge-Transfer Mixing for Efficient Hot-Exciton Emission with Improved Color Purity.

Delayed fluorescence (DF) emitters with high color purity are of high interest for applications in high-resolution displays. However, the charge transfer required by high emitting efficiency usually conflicts with the expected color purity. In this work, we investigated the S 1 /S 0 conformational relaxation, spin-orbital coupling (SOC), and vibronic coupling of hot-exciton emitters while hybrid local and charge transfer (HLCT) state tuning was achieved by a structural meta -effect. The meta- linkage leads to suppressed S 1 /S 0 conformational relaxation and weakened vibronic coupling, while the unsacrificed emitting efficiency is largely ensured by multiple rISC channels (T n → S m ) with thermally accessible triplet-singlet energy gap (Δ E ST ) and effective SOC. We demonstrated that the unique excited-state mechanism provides opportunities to improve the emitting color purity of hot-exciton emitters without sacrificing emitting efficiency by HLCT state tuning with simple chemical structural modification, for which hot-exciton emitters might play a more important role for high-resolution organic light-emitting diode displays.