Modulation of Carbazole/Phenol Resonant Partners within Diboron‐Based Multi‐Resonance Emitters Enable High‐Performance Narrowband Green to Red OLEDs

Abstract Diboron‐based multi‐resonance (MR) molecules featuring para ‐B‐π‐B configuration represent a highly promising class of emitters for red and near‐infrared organic light‐emitting diodes (OLEDs). The emission spectra of the diboron‐based MR emitters can be fine‐tuned by modulating the carbazole/phenol resonant partners. However, beyond spectral tuning, a comprehensive understanding of the intricate relationship between molecular structure, and the overall properties of diboron‐based MR emitters remains elusive. In this work, through meticulous molecular design and precise material synthesis, the study has constructed three new MR emitters and completed the establishment of the diboron‐based MR molecular family involving a carbazole/phenol resonant counterpart. These emitters facilitate a systematic investigation into the comprehensive impact of resonant partners on critical properties beyond spectral tuning, such as thermally activated delayed fluorescence, full‐width at half‐maximum, and horizontal orientation ratio. Eventually, by employing these emitters, high‐performance narrowband emitting OLEDs with maximum external quantum efficiencies (EQE max s) of 30.2%, 33.0%, and 37.0% are fabricated for the green, yellow, and red devices, respectively, together with exceptional operational lifetimes. In particular, both yellow and red OLEDs exhibit unprecedented low‐efficiency roll‐off, maintaining high EQEs over 30% and 25% at the ultrahigh brightness levels of 10 000 and 100 000 cd m −2 , respectively.