Realizing Record‐High Electroluminescence Efficiency of 31.5 % for Red Thermally Activated Delayed Fluorescence Molecules

• Published in: Angewandte Chemie International Edition 2021-10, Vol.60 (44), p.23635-23640
• Main Authors: Cai, Zheyi, Wu, Xing, Liu, Hao, Guo, Jingjing, Yang, Dezhi, Ma, Dongge, Zhao, Zujin, Tang, Ben Zhong
• Format: Article
• Language: English
• Subjects: Coupling (molecular); Coupling factors; Dipoles; Display devices; Doped films; Electroluminescence; Emissions; Fluorescence; horizontal dipole orientation; Horizontal orientation; intramolecular hydrogen bonding; Near infrared radiation; organic light-emitting diodes; Photoluminescence; Photons; red luminescent materials; thermally activated delay fluorescence
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202111172

Tailor‐made red thermally activated delayed fluorescence (TADF) molecules comprised of an electron‐withdrawing pyrazino[2,3‐f][1,10]phenanthroline‐2,3‐dicarbonitrile core and various electron‐donating triarylamines are developed. They can form intramolecular hydrogen‐bonding, which is conducive to improving emission efficiency and promoting horizontal orientation and show near infrared (NIR) emissions (692–710 nm) in neat films and red delayed fluorescence (606–630 nm) with high photoluminescence quantum yields (73–90%) in doped films. They prefer horizontal orientation with large horizontal dipole ratios in films, rendering high optical out‐coupling factors (0.39–0.41). Their non‐doped OLEDs exhibit NIR lights (716–748 nm) with maximum external quantum efficiencies (ηext,max) of 1.0–1.9%. And their doped OLEDs radiate red lights (606–648 nm) and achieve record‐beating ηext,max of up to 31.5%. These new red TADF materials should have great potentials in display and lighting devices. Tailor‐made red thermally activated delayed fluorescence molecules with intramolecular hydrogen bonding are developed, which exhibit excellent photoluminescence efficiencies and large horizontal dipole ratios, and thus furnish the state‐of‐the‐art red and near infrared OLEDs, with a record‐high external quantum efficiency of 31.5 %.