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

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.