Boron‐Based Narrowband Multiresonance Delayed Fluorescent Emitters for Organic Light‐Emitting Diodes

Recently, the exploration of boron (B)/heteroatom‐embedded polycyclic nanographites featuring multiresonance thermally activated delayed fluorescence (MR‐TADF) garners astonishing attention to promote the advancement of organic light‐emitting diodes (OLEDs). Contrary to the traditional donor–acceptor (D–A)‐type TADF emitters, the MR‐TADF emitters manifest narrowband emission with full width at half maximum (FWHM ≤ 40 nm) and superior photoluminescence quantum yield (PLQY) coupled with the small singlet–triplet energy splitting, which appeal their potential as promising candidates in fabricating efficient OLEDs. Growingly, MR‐TADF emitters deliver benchmark device performance comparable to the conventional TADF/phosphorescent emitters. However, they are suffering from the major drawbacks such as difficult to realize full‐color emitters, slow exciton upconversion dynamics, aggregation‐caused emission quenching, severe efficiency roll‐off, and poor operational lifetime, which jeopardizes their practical applicability. Herein, a comprehensive review on B‐based MR‐TADF emitters reported till date is presented, focusing on the different design strategies documented for circumventing the aforementioned shortcomings. This review is divided into several subgroups based on the emission color of the materials to draw the attention of organic electronics community toward constructing efficient full‐color MR‐OLEDs. Finally, challenges and opportunities in the MR‐TADF emitters are discussed.