Spiro‐fluoreno‐imidazole (SFI) Emitters Efficiently Harvesting Hot Excitons for Deep‐Blue Organic Light‐Emitting Diodes with CIE y Below 0.046

. Remarkably, the tCz-SFI-based OLED device achieved deep-blue electroluminescence with an exciton utilization efficiency of 83.2% and an unprecedented external quantum efficiency of 12.55% by efficiently harvesting hot triplet excitons. The device exhibited stable electroluminescence peaking at 410 nm, corresponding to Commission Internationale de l'Eclairage coordinates of (0.161, 0.043), setting a new benchmark for deep-blue hot-exciton OLEDs.