The development of high-performance blue organic light-emitting diodes (OLEDs) is impeded by the scarcity of molecular scaffolds for ultranarrow multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters and their inherent tendency to suffer from aggregation-induced broadening and quenching in solid films. To intrinsically address these dual challenges, we report a "soft constraints" molecular design strategy that strategically enhances intramolecular noncovalent interactions. By appending tailored donor (carbazole) or acceptor (triazine) units to the MR-TADF core, this architecture not only directly suppresses key high-frequency vibrations (e.g., C─N stretching) to achieve an impressively narrow emission with a full width at half-maximum (FWHM) of 19 nm in solution, but also effectively inhibits detrimental π…π stacking between the emissive cores. The resulting emitters Cz‑TBN and TRZ‑TBN retain ultranarrow emission (FWHM ≈ 23 nm) and high external quantum efficiencies (up to 40.5%) in OLEDs across a broad doping range (1-10 wt%); the TRZ‑TBN device also reaches a record power efficiency (67.9 lm W-1) for blue MR-OLEDs. This work offers a generalizable strategy for the rational design of high-performance blue emitters.
Qu et al. (Sat,) studied this question.