Suppression of aggregation-caused quenching in multiple resonance thermally activated delayed fluorescence emitters through tert-butyl and carbazole incorporation

Abstract

Quinolino[3,2,1-de]acridine-5,9-dione (QAO), a multiple resonance thermally activated delayed fluorescence (MR-TADF) emitter, is extensively researched on due to its excellent TADF properties including a favourable singlet-triplet energy gap (ΔE ST), narrowband emission, remarkable photoluminescence quantum yield (PLQY), and tuning emission characteristics. However, its inherently planar structure leads to aggregation-caused quenching (ACQ), which significantly reduces its PLQY. Herein, three novel MR-TADF molecules are designed and synthesised based on the QAO core. These new emitters – tBuQAO, tBuQAO-Cz, and tBuQAO-2Cz – exhibit outstanding MR-TADF properties, including narrow band emissions that have small full width at half-maximum (FWHM) values of 31 nm, 26 nm, and 28 nm respectively. They also feature small ΔE ST values of 0.24 eV, 0.25 eV, and 0.23 eV, alongside high PLQYs of 85%, 95%, and 93%, respectively, when doped at 1 wt.% in polymethyl methacrylate (PMMA) films. Importantly, these emitters maintain their high PLQYs even at increased doping concentrations of up to 20 wt.%, demonstrating that the incorporation of tert-butyl and carbazole groups effectively mitigates ACQ.