AUTHOR=Mubarok Hanif , Lee Woochan , Lee Taehwan , Jung Jaehoon , Yoo Seunghyup , Lee Min Hyung 

TITLE=Impact of Boron Acceptors on the TADF Properties of Ortho-Donor-Appended Triarylboron Emitters

JOURNAL=Frontiers in Chemistry

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.00538

DOI=10.3389/fchem.2020.00538

ISSN=2296-2646

ABSTRACT=<p>We report the impact of boron acceptors on the thermally activated delayed fluorescence (TADF) properties of <italic>ortho</italic>-donor-appended triarylboron compounds. Different boryl acceptor moieties, such as 9-boraanthryl (<bold>1</bold>), 10<italic>H</italic>-phenoxaboryl (<bold>2</bold>), and dimesitylboryl (BMes<sub>2</sub>, <bold>3</bold>) groups have been introduced into an <italic>ortho</italic> donor (D)–acceptor (A) backbone structure containing a 9,9-diphenylacridine (DPAC) donor. X-ray crystal diffraction and NMR spectroscopy evidence the presence of steric congestion around the boron atom along with a highly twisted D–A structure. A short contact of 2.906 Å between the <italic>N</italic> and <italic>B</italic> atoms, which is indicative of an N → B nonbonding electronic interaction, is observed in the crystal structure of <bold>2</bold>. All compounds are highly emissive (PLQYs = 90–99%) and display strong TADF properties in both solution and solid state. The fluorescence bands of cyclic boryl-containing <bold>1</bold> and <bold>2</bold> are substantially blue-shifted compared to that of BMes<sub>2</sub>-containing <bold>3</bold>. In particular, the PL emission bandwidths of <bold>1</bold> and <bold>2</bold> are narrower than that of <bold>3</bold>. High-efficiency TADF-OLEDs are realized using <bold>1</bold>–<bold>3</bold> as emitters. Among them, the devices based on the cyclic boryl emitters exhibit pure blue electroluminescence (EL) and narrower EL bands than the device with <bold>3</bold>. Furthermore, the device fabricated with emitter <bold>1</bold> achieves a high external quantum efficiency of 25.8%.</p>