Designing a Deep Blue Emitter by Disrupting Phenanthroimidazole Conjugation for Non‐Doped OLEDs with an External Quantum Efficiency > 13%

The pursuit of highly efficient non‐doped organic light‐emitting diodes (OLEDs) has promoted the development of blue emitters with a design strategy. In this study, we developed a deep blue emitter featuring hybridized local and charge‐transfer characteristics. The blue emitter, PIMAnCz, consists of a molecular framework of a disrupted phenanthroimidazole moiety, which resulted in large steric hindrance and reduced electron delocalization along the fragments. These features lead to a high spin‐orbit coupling between the high‐lying triplet level and low‐lying singlet level (S 1 ) and a photoluminescence of 59%. More importantly, the non‐doped device employing a neat PIMAnCz emitting layer delivered a maximum external quantum efficiency of 13.19% with Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.09), placing it among the highest efficiencies attained for a non‐doped deep blue OLED with CIE y < 0.10. These findings provide practical design insights for a highly efficient blue emitter for non‐doped deep blue OLED applications.