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

Abstract

We report the impact of boron acceptors on the thermally activated delayed fluorescence (TADF) properties ofortho-donor-appended triarylboron compounds. Different boryl acceptor moieties, such as 9-boraanthryl (1), 10H-phenoxaboryl (2), and dimesitylboryl (BMes(2),3) groups have been introduced into anorthodonor (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 angstrom between theNandBatoms, which is indicative of an N -> B nonbonding electronic interaction, is observed in the crystal structure of2. 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-containing1and2are substantially blue-shifted compared to that of BMes(2)-containing3. In particular, the PL emission bandwidths of1and2are narrower than that of3. High-efficiency TADF-OLEDs are realized using1-3as emitters. Among them, the devices based on the cyclic boryl emitters exhibit pure blue electroluminescence (EL) and narrower EL bands than the device with3. Furthermore, the device fabricated with emitter1achieves a high external quantum efficiency of 25.8%.