Synthesis of Conjugated Tris- and Tetrakis (Carbazolyl) Azulenes with Intense Emission in the Visible Range

New conjugated carbazolyl-substituted azulenes, such as 1,2,3-tris(carbazolyl)azulene and 1,2,3,6-tetrakis(carbazolyl)azulene, were synthesized via cross-coupling reactions in high yields. The resulting compounds exhibit a significant ability to absorb and emit light in the visible region, in the range of 400 to 600 nanometers. Studies have shown that azulene with carbazolyl substituents at positions 1, 2, 3, and 6 possesses unique photophysical properties, manifested as intense emission in the blue photoluminescence region (λ_PL at 444 and 490 nm), which is not observed in the original azulene. This feature arises due to the donor properties of carbazolyl substituents, which have a strong effect on the electronic structure of azulene, creating the conditions for a permitted HOMO-LUMO electronic transition.