cis‐Quinacridone‐Based Delayed Fluorescence Emitters: Seemingly Old but Renewed Functional Luminogens

Herein, we report a material design of linear cis‐quinacridone (cis‐QA) derivatives as delayed fluorescence luminogens. In contrast to the widely studied traditional trans‐isomers, the functionality of cis‐QA and its derivatives remains unexplored and unclarified. Through combined computational and experimental investigations, we revealed that cis‐QA derivatives can function as fascinating narrowband deep‐blue delayed fluorescence emitters for organic light‐emitting diodes (OLEDs). The best‐performing deep‐blue OLEDs incorporating these cis‐QA luminogens achieved high external electroluminescence quantum efficiencies of up to 19.0 % and high color purity with chromaticity coordinates of (0.13, 0.14). Linear cis‐quinacridone (cis‐QA), a structural isomer of the renowned linear trans‐quinacridone with a variation in the substitution positions of two amino and carbonyl groups, has been in a state of low visibility and unmarked as functional materials for a century. This contribution unveils the fascinating functionality and usefulness of cis‐QA derivatives as narrowband deep‐blue delayed fluorescence emitters.