Adamantane-Bridged Boron-Nitrogen-based Multi-Resonance TADF Emitters for Narrowband Green OLEDs with Extended Operating Lifetime

For existing multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules, expanding aromatic planes via intramolecular cyclization have become general strategies to modify structures, yet enhancing molecular stability remains challenging. Herein, we report the first pure-green MR emitter incorporating an adamantane moiety as an intramolecular cyclization locker, not only modulating emission colors but also achieving remarkable operation stability alongside high efficiency in organic light-emitting diodes (OLEDs). Ada-ICzBN obtains narrowband emission at 526 nm with full width at half maximum (FWHM) of 26 nm in toluene, which could be maintained in highly doped films (16 wt%) due to the three-dimensional steric hindrance of adamantane. Corresponding OLED achieved maximum external quantum efficiency of 31.9% with negligible efficiency roll-off (29.0% at 1,000 cd/m², 26.1% at 10,000 cd/m²), an ultrahigh maximum brightness of 3.6×10⁵ cd/m², and high color-purity with a chromaticity y-coordinate of 0.70. Notably, an exceptionally long operational lifetime of 769 h to 90% of its initial 1,000 cd/m² is obtained, over sixfold longer than the reference emitter with a commonly adopted spiro-fluorene. Theoretical investigations attribute this to the effective confinement of frontier molecular orbitals within the core MR skeleton, facilitated by the saturated sp³ carbon atoms of the adamantane participating minimally in orbital delocalization.