Novel Robust Folded Thermally Activated Delayed Fluorescence Molecules for High-Performance OLEDs

Folded thermally activated delayed fluorescence (TADF) molecules based on through-space charge transfer (TSCT) have aroused increasing interest, but the electroluminescence (EL) efficiencies of most folded TADF molecules are still inferior, and their application as sensitizers for multi-resonance TADF (MR-TADF) emitters remains barely explored. Herein, two novel isomeric folded TADF molecules, f-TRZ-1 and f-TRZ-2, are constructed by using 2,4,6-triphenyl-1,3,5-triazine (TRZ) as acceptor, 9-phenylcarbazole (PC) as donor, and 11,12-dihydroindolo[2,3-a]carbazole (HIC) as bridge. They exhibit regular intramolecular packing structures with effective TSCT and enjoy ultrahigh thermal stability and balanced bipolar charge transport. Moreover, efficient organic light-emitting diodes (OLEDs) are fabricated using f-TRZ-1 and f-TRZ-2 as emitters, achieving maximum external quantum efficiencies (η_ext,max) of up to 28.9%. f-TRZ-1 and f-TRZ-2 can perform as efficient sensitizers for the green MR-TADF emitter tCzphB-Fl, and the prepared hyperfluorescence OLEDs exhibit outstanding EL performances, with improved η_ext,maxs of up to 37.8% and reduced efficiency roll-offs. This work demonstrates the promising potential of these folded TADF molecules as emitters and sensitizers for the fabrication of high-performance OLEDs.