A Deep‐Blue‐Emitting Heteroatom‐Doped MR‐TADF Nonacene for High‐Performance Organic Light‐Emitting Diodes**

Abstract We present a p‐ and n‐doped nonacene compound, NOBNacene, that represents a rare example of a linearly extended ladder‐type multiresonant thermally activated delayed fluorescence (MR‐TADF) emitter. This compound shows efficient narrow deep blue emission, with a λ PL of 410 nm, full width at half maximum, FWHM, of 38 nm, photoluminescence quantum yield, Φ PL of 71 %, and a delayed lifetime, τ d of 1.18 ms in 1.5 wt % TSPO1 thin film. The organic light‐emitting diode (OLED) using this compound as the emitter shows a comparable electroluminescence spectrum peaked at 409 nm (FWHM=37 nm) and a maximum external quantum efficiency (EQE max ) of 8.5 % at Commission Internationale de l’Éclairage (CIE) coordinates of (0.173, 0.055). The EQE max values were increased to 11.2 % at 3 wt % doping of the emitter within the emissive layer of the device. At this concentration, the electroluminescence spectrum broadened slightly, leading to CIE coordinates of (0.176, 0.068).