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

We report the impact of boron acceptors on the thermally activated delayed fluorescence (TADF) properties of -donor-appended triarylboron compounds. Different boryl acceptor moieties, such as 9-boraanthryl (), 10-phenoxaboryl (), and dimesitylboryl (BMes, ) groups have been introduced into an 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 and atoms, which is indicative of an N → B nonbonding electronic interaction, is observed in the crystal structure of . 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 and are substantially blue-shifted compared to that of BMes-containing . In particular, the PL emission bandwidths of and are narrower than that of . High-efficiency TADF-OLEDs are realized using - 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 . Furthermore, the device fabricated with emitter achieves a high external quantum efficiency of 25.8%.