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 (1H, 11B, 13C) 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. Molecules comprising benzodiazaborole and carbazole units either directly linked by a B–N bond or connected through a thiophene spacer were synthesized from 2‐bromoboroles and the corresponding lithium amide or lithium thienyl. The structures and photophysical properties were studied experimentally as well as by DFT.