Nitrogen-containing polycyclic heteroaromatics have exhibited fascinating multi-resonance (MR) characteristics for efficient narrowband emission, but strategies to bathochromic shift their emissions while maintaining the narrow bandwidths remain exclusive. Here, homogeneous hexatomic rings are introduced into nitrogen-embedded MR skeletons to prolong the π-conjugation length for low-energy electronic transitions while retaining the non-bonding character of the remaining parts. The proof-of-the-concept emitters exhibit near unity photoluminescence quantum yields with peaks at 598 nm and 620 nm and small full-width-at-half-maximums of 28 nm and 31 nm, respectively. Optimal organic light-emitting diodes exhibit a high external quantum efficiency of 18.2 %, negligible efficiency roll-off, and ultra-long lifetime with negligible degradation at an initial luminance of 10 000 cd m-2 after 94 hours.
Keywords: Bathochromic Shift; Device Stability; Homogeneous Hexatomic Rings; Multiple Resonance; Narrow Energy Gap.
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