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

• Published in: Advanced optical materials 2023-08, Vol.11 (16), p.n/a
• Main Authors: Luo, Ming, Li, Wei, Du, Songyu, Zhang, Jiasen, Wang, Zhichuan, Zhang, Xiaoli, Li, Yong, Ge, Ziyi
• Format: Article
• Language: English
• Subjects: Benzonitrile; Charge transfer; Color; Emission; Emitters; Materials science; multiple‐resonance; Nitrogen; Optics; organic electronics; organic light‐emitting diodes; polycyclic aromatic hydrocarbons; Purity; Quantum efficiency; Resonance
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202300491

For purely nitrogen‐based multi‐resonance emitters (N‐MR), strategies to integrate emission modulation with high color purity remain exclusive, especially in near‐ultraviolet (NUV) regions. Herein, it is demonstrated for the first time that rationally introducing weak intramolecular charge transfer (ICT) to the MR skeleton to modulate the emission from violet to deep‐blue while retaining high color purity is feasible. By replacing the middle phenyl moiety with the pyridine or benzonitrile unit in the solely nitrogen‐based violet MR skeleton of tDIDCz, two proof‐of‐concept emitters, Nm‐ICz and CNm‐ICz, emphasizing mixed excited states of localized excited (LE) transition from the original MR skeleton and emergent transition channel with charge‐transfer (CT) character, successfully realize bathochromic‐shift and polarity‐insensitive fluorescence from 395 nm to 404–407 and 419–421 nm, respectively, while retaining small full‐width at half‐maximums (FWHMs) of 28–37 and 33–43 nm (214‐281 and 237–310 meV). Furthermore, Nm‐ICz shows bright and violet electroluminescence (EL) spectrum with the peak at 412 nm, while CNm‐ICz shows high color purity deep‐blue EL spectrum with the peak at 427 nm, a small FWHM of 42 nm (286 meV), an ultralow y color coordinate of 0.027, and a maximum external quantum efficiency (EQEmax) of 3.7%. Benefiting from the rational intramolecular charge transfer introduced into the multi‐resonance skeleton, fine modulation of emission color is achieved from 395 to 421 nm while retaining small full‐width at half‐maximums of 28 and 33 nm (214 and 237 meV), enabling the bright violet organic light‐emitting diode (OLED) with the peak at 412 nm and the deep‐blue OLED with the peak at 427 nm and an ultralow CIEy of 0.027, both of which show alleviated efficiency roll‐off.