A B–N bond-doped multiple resonance emitter with extended π-conjugation for narrowband sky-blue OLEDs exhibiting low efficiency roll-off

Abstract

Incorporating B–N covalent bonds into the classic boron–nitrogen multiple resonance (B,N-MR) skeleton within a polycyclic heteroaromatic framework presents an effective approach for developing novel narrowband MR emitters. In this study, the synthesis process was simplified using a lithium-free one-pot borylation reaction, yielding a narrowband MR emitter, ICz[B–N], featuring an indolocarbazole segment to extend π-conjugation and induce a redshifted emission. The para-positioned nitrogen–π–nitrogen conjugation in the indolocarbazole segment exhibits enhanced electron-donating ability relative to the traditional carbazole moiety, while the rigidly extended MR backbone enables both spectral redshift and narrowband emission. The synthesized ICz[B–N] displayed sky-blue emission at 488 nm, representing a 42 nm redshift relative to B,N-MR blue emitter doping with the B–N bond, while maintaining a narrow spectral linewidth of only 19 nm. The corresponding sensitized OLED device achieved a peak brightness exceeding 70 000 cd m⁻², an external quantum efficiency of 15.0%, and minimal efficiency roll-off.