Purely Nitrogen-Based Multi-Resonance Deep-Blue Emitter with an Ultralow y Color Coordinate of 0.03 via Rationally Intramolecular Charge Transfer

摘要

For purely nitrogen-based multi-resonance emitters (N-MR), strategies tointegrate emission modulation with high color purity remain exclusive,especially in near-ultraviolet (NUV) regions. Herein, it is demonstrated for thefirst time that rationally introducing weak intramolecular charge transfer (ICT)to the MR skeleton to modulate the emission from violet to deep-blue whileretaining high color purity is feasible. By replacing the middle phenyl moietywith the pyridine or benzonitrile unit in the solely nitrogen-based violet MRskeleton of tDIDCz, two proof-of-concept emitters, Nm-ICz and CNm-ICz,emphasizing mixed excited states of localized excited (LE) transition from theoriginal MR skeleton and emergent transition channel with charge-transfer(CT) character, successfully realize bathochromic-shift and polarity-insensitivefluorescence from 395 nm to 404–407 and 419–421 nm, respectively, whileretaining small full-width at half-maximums (FWHMs) of 28–37 and33–43 nm (214-281 and 237–310 meV). Furthermore, Nm-ICz shows brightand violet electroluminescence (EL) spectrum with the peak at 412 nm, whileCNm-ICz shows high color purity deep-blue EL spectrum with the peak at427 nm, a small FWHM of 42 nm (286 meV), an ultralow y color coordinate of0.027, and a maximum external quantum efficiency (EQEmax) of 3.7.