Synthetic, Structural, Photophysical and Computational Studies on π-Conjugated 1,3,2-Benzodiazaboroles with Carbazole Building Blocks

The reaction of the N-lithiated 3,6-di-tert-butyl-carbazole (2) with 2-bromo-1,3-diethyl-1,3,2-benzodiazaborole (1a) and 2-bromo-1,3-diphenyl-1,3,2-benzodiazaborole (1b) afforded the 2-N-carbazolyl-functionalized benzodiazaboroles 3a and 3b as colourless solids in 77 and 73% yield, respectively. Synthesis of 2[5'-N-carbazolyl-2'-thienyl]-1,3-diethyl-1,3,2-benzodiazaborole (5a) was effected by lithiation of N-(2-thienyl)carbazole (4) and subsequent reaction with equimolar amounts of 1a, and 5a was obtained in 68% yield. Similarly, 2[5'-N-carbazolyl-2'-thienyl]-1,3-diphenyl-1,3,2-benzodiazaborole (5b) was prepared from lithiated 4 and 1b in 62% yield. Compounds 3a,b and 5a,b are characterized by elemental analyses, IR and NMR spectroscopy (H-1, B-11, C-13) and mass spectrometry. The molecular structures of 3a and 5a were elucidated by X-ray diffraction analysis. These borylated systems show intense blue luminescence. The spectroscopic results were reproduced by TD-DFT calculations at the [B3LYP/6-311G (d,p)] level of theory.