One‐Pot Synthesis of Twisted Helical and Quasi‐Planar Boron‐Nitrogen Doped Polycyclic Aromatic Hydrocarbons for Narrowband Electroluminescence

Heteroatom-doped polycyclic aromatic hydrocarbons (PAHs) with special topological structures have garnered significant attention owing to the effective regulation of photophysical properties of emitters at the molecular level. Herein, we report the design and one-pot synthesis of two heteroatom-doped PAHs, namely 4BN with a twisted helical configuration and 3BN with a quasi-planar configuration. Systematic structure-property investigations reveal that molecular topology plays a decisive role in governing intrinsic electronic structures and intermolecular interactions. The quadruple-borylated 4BN with rigid PAH skeleton effectively suppresses structural relaxation and electron-vibrational coupling via manipulating the non-bonding characteristics, thereby affording ultra-narrowband emission. Consequently, for 4BN, the full widths at half maximum (FWHMs) as narrow as 13 nm in toluene solution and 14 nm in solution-processed electroluminescence device are achieved, representing the narrowest FWHM reported to date for OLEDs based on multiple resonance (MR) emitters. Furthermore, in TADF-assisted solution-processed device, the emission spectrum slightly broadens to 15 nm with a maximum external quantum efficiency (EQE_max) of 18.9%. In sharp contrast, the triple-borylated 3BN with quasi-planar geometry shows enhanced π-delocalization and stronger vibronic coupling, resulting in broader FWHM of 25 nm in TADF-assisted solution-processed devices with an EQE_max of 19.8%.