A research team led by Professor Wang Dongdong from the School of Chemistry at Xi'an Jiaotong University (XJTU) has proposed a novel nitrogen-mediated, orbital-compatible π-extension strategy.

By using the electronic effects of pyridine-type sp²-hybridized nitrogen atoms, this strategy precisely modulates the frontier orbital distribution within the π-extension unit to construct resonance-like orbital segments that are highly matched with the BN-type MR core.

This enables the multiple resonance effect to propagate across the entire molecular skeleton, causing an emission redshift while effectively suppressing spectral broadening.

Based on this design concept, the team synthesized and systematically screened a series of derivatives, among which BNCz-PQ demonstrated exceptional overall performance: it exhibits an emission peak at 511 nm with a narrow full width at half maximum (FWHM) of just 24 nm.

Furthermore, the fabricated phosphorescent-sensitized OLED devices achieved a maximum external quantum efficiency (EQE) of 27.7 percent, a maximum luminance of 153,400 cd m⁻², and excellent operational stability, maintaining an EQE of 23.6 percent even at a high luminance of 10,000 cd m⁻². These comprehensive performance metrics rank among the state-of-the-art for similar materials internationally.

This study establishes a universal, orbital-guided molecular design principle, offering a novel approach to solving the spectral broadening challenge in traditional π-extended systems and holding significant implications for advancing high-color-purity, narrowband OLED materials.

The research results were published in the top international chemistry journal Angewandte Chemie International Edition under the title Nitrogen-Mediated Orbital-Compatible π-Extension: Balancing Excited-State Components and Suppressing Vibrational Broadening Toward Redshifted Narrowband MR-TADF Emitters.