AUTHOR=Bae Jaehyun , Sakai Mika , Tsuchiya Youichi , Ando Naoki , Chen Xian-Kai , Nguyen Thanh Ba , Chan Chin-Yiu , Lee Yi-Ting , Auffray Morgan , Nakanotani Hajime , Yamaguchi Shigehiro , Adachi Chihaya 

TITLE=Multiple resonance type thermally activated delayed fluorescence by dibenzo [1,4] azaborine derivatives

JOURNAL=Frontiers in Chemistry

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.990918

DOI=10.3389/fchem.2022.990918

ISSN=2296-2646

ABSTRACT=<p>We studied the photophysical and electroluminescent (EL) characteristics of a series of azaborine derivatives having a pair of boron and nitrogen aimed at the multi-resonance (MR) effect. The computational study with the STEOM-DLPNO-CCSD method clarified that the combination of a BN ring-fusion and a terminal carbazole enhanced the MR effect and spin-orbit coupling matrix element (SOCME), simultaneously. Also, we clarified that the second triplet excited state (T<sub>2</sub>) plays an important role in efficient MR-based thermally activated delayed fluorescence (TADF). Furthermore, we obtained a blue–violet OLED with an external EL quantum efficiency (EQE) of 9.1%, implying the presence of a pronounced nonradiative decay path from the lowest triplet excited state (T<sub>1</sub>).</p>