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

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 (λPL of 491 nm) with a full-width at half-maximum of 33 nm and a RISC rate constant (kRISC) of 1.37 × 106 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 (EQEmax) 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 EQEmax decreasing from 7.0 to 2.7% as the doping concentration increases from 1 to 5 wt%.