Efficient narrowband bluish-green emitters derived from a double-carbazole-fused organoboron multiple resonance skeleton with internal-structure modification

Abstract

The double-carbazole-fused organoboron framework CzBN is a widely used parent skeleton in designs of multiple resonance (MR) emitters. Currently, the majority of CzBN derivatives are derived from peripheral modification strategies. Here, we focus on internal-structure modification of the CzBN skeleton and thus develop two narrowband bluish-green MR emitters by directly embedding thiophene units into the CzBN skeleton. This incorporation of thiophene units not only extends the π-conjugated backbone towards red-shifted emission, but also improves the MR characteristics and structural rigidity for narrowband features. Both emitters achieve narrowband bluish-green emissions with extremely small full width at half maximum of ca. 23 nm in dilute toluene. Moreover, the optimized sensitized device based on BTPCzBN as the terminal emitter achieves a high maximum external quantum efficiency of up to 24% with suppressed efficiency roll-off. This work not only presents a distinct strategy for the development of CzBN derivatives via internal-structure modification of MR skeletons, but also provides valuable inspiration for the design of heteroatom-fused narrowband emitters.