Triarylboranes bearing a benzimidazole or quinoline ring attached to the boron atom: Synthesis, π-conjugation, and fluorescence

2-Aryl-6-(dimesitylboryl)-5,7-dimethylbenzimidazoles (1), 2-aryl-5-(dimesitylboryl)-1,4,6-trimethylbenzimidazoles (2), and 2-aryl-6-(dimesitylboryl)-3,5,7-trimethylquinolines (3) were synthesized by imine formation from 4-(dimesitylboryl)-3,5-dimethylaniline (4) and a subsequent intramolecular cyclization reaction affording benzimidazole or quinoline rings. The degree of π-conjugation and fluorescence properties of the obtained triarylboranes were evaluated to develop easily synthesizable fluorescent triarylboranes using imine formation. Compounds 1–3 exhibited blue fluorescence (λ_em, 389–425 nm) with moderate fluorescence quantum yields (Φ_F, 8%–49%) in chloroform.