Reduced Concentration Quenching of Multi‐Resonant Thermally Activated Delayed Fluorescence Emitter Incorporating Pillar[5]Arene Macrocycle

ABSTRACT The development of multi‐resonant thermally activated delayed fluorescence (MR‐TADF) emitters, which simultaneously exhibit narrowband emission, suppressed concentration quenching, and rapid reverse intersystem crossing (RISC), remains a challenge. Here, an MR‐TADF emitter incorporating pillar[5]arene to suppress aggregation is reported. The “butterfly” shaped emitter BN‐APOPV is constructed by tethering pillar[5]arene to a tCzBN MR‐TADF skeleton and employing an aryl bridge for connection. Intramolecular energy transfer and TADF type CzAcSF host materials are used to harvest excitons and accelerate RISC. BN‐APOPV exhibits sky‐blue emission (λ PL of 491 nm) with a full‐width at half‐maximum of 33 nm and a RISC rate constant ( k RISC ) of 1.37 × 10 6 s −1 in a 1 wt% doped CzAcSF film. As the doping concentration is increased from 1 to 5 wt%, the photoluminescence quantum yield increases from 76% to 86%. Solution‐processed organic light‐emitting diodes prepared with BN‐APOPV exhibited almost the same maximum external quantum efficiencies (EQE max ) of 9% at doping concentrations ranging from 1 to 5 wt%. In contrast, the device doped with the emitter BN‐AOPV (prepared without pillar[5]arene ) suffers from severe aggregation‐caused quenching with EQE max decreasing from 7.0 to 2.7% as the doping concentration increases from 1 to 5 wt%.