The syntheses of AZB and the two targeted emitters are shown in Scheme 1. The key benzylprotected precursor, 5-benzyl-10-mesityl-5,10-dihydrodibenzo[b,e] [1,4]azaborinine (1), was readily prepared by reacting N-benzyl-2-bromo-N-(2-bromophenyl)aniline with 2.1 equivalents of n-butyllithium followed by quenching with dimethyl mesitylboronate. Debenzylation proceeded using Pd/C under a H2 atmosphere at room temperature to furnish 10-mesityl-5,10dihydrodibenzo[b,e][1,4]azaborinine (2) in 20% yield; significant unreacted starting material was also recovered. The target emitters AZB-Ph-TRZ and AZB-TRZ were synthesized from 2 and the corresponding triazine derivatives via a Buchwald-Hartwig cross-coupling reaction in moderate-to-good yields. The two compounds were purified first by column chromatography and then by temperature-gradient vacuum sublimation. The identity and purity of the two emitters were determined from a combination of 1 H and 13 C NMR spectrometry, high-resolution mass spectrometry (HRMS), elemental analysis (EA), high-performance liquid chromatography (HPLC) and melting point determination (Figures ).