Pentagonal/Heptagonal‐Lock Strategy Enables Narrowband Red Multiple Resonance Emitters Through Temperature‐Controlled Scholl Reaction

Abstract Although π‐extension has shown considerable success in achieving red‐shifted emission in multiple resonance (MR) emitters, it often induces substantial spectral broadening, thereby limiting its utility for developing high‐performance red MR materials. Herein, we report a straightforward naphthalene‐based pentagonal/heptagonal‐lock π‐extension strategy that enables a significant redshift of 116 nm while maintaining a narrow emission bandwidth. By controlling the Scholl reaction at different temperatures, we achieved precise π‐extension through sequential pentagonal and heptagonal ring formation, enabling broad color tuning via fine adjustment of frontier molecular orbital energy gaps. As a result, a red fluorescent emitter was obtained, exhibiting an emission peak at 600 nm and a narrow full‐width‐at‐half‐maximum of 30 nm. Furthermore, the corresponding OLED devices exhibited a high external quantum efficiency of 21.3% with minimal efficiency roll‐off.