Conjugation Pathway Management in Hybrid Multi-resonance Thermally Activated Delayed Fluorescent Emitters for Horizontal Emitting Dipole Orientation

The development of deep-blue emitters with both high
efficiency
and excellent color purity remains a challenge in organic light-emitting
diode (OLED). Herein, we report a novel hybrid multi-resonance (MR)
thermally activated delayed fluorescence (TADF) emitter, BN-o-OICz, with a boron-based
MR core conjugated to indolo[3,2,1-jk]carbazole which introduces a
zigzag conjugation pathway that extends the MR framework and enhances
charge-transfer delocalization. BN-o-OICz shows a small singlet–triplet
energy gap, high oscillator strength, and large transition dipole
moment alignment through conjugation pathway management, resulting
in increased horizontal dipole orientation and reduced device efficiency
roll-off. The OLED based on BN-o-OICz demonstrates a deep-blue emission at
456 nm with a fwhm of 25 nm and a high external quantum efficiency
of 31.0%. These results underscore the importance of tuning the conjugation
pathway to optimize MR-TADF properties and provide an effective strategy
for high-performance deep-blue OLEDs.