Azulene‐Embedded [<i>n</i>]Helicenes (<i>n</i>=5, 6 and 7)
Chao Duan, Jianwei Zhang, Junjun Xiang, Xiaodi Yang, Xike Gao
Abstract
Abstract Azulene is a non‐benzenoid aromatic building block with unique chemical structure and physicochemical properties. By using the “bottom‐up” synthetic strategy, we synthesized three azulene‐embedded [ n ]helicenes ( [ n ]AzHs , n =5, 6 and 7), in which one terminal azulene subunit was fused with n ‐ 2 benzene rings. P‐ and M‐ enantiomers were observed in the packing diagrams of [5]‐ , and [6]AzHs . However, P ‐ and M ‐ [7]AzHs could be isolated by recrystallization of the racemic mixture. These [ n ]AzHs were endowed with new properties through the azulene moiety such as low‐lying first electric state (S 1 ), small optical energy gap and anti‐ Kasha emission. [6]‐ , and [7]AzHs exhibit strong chiroptical responses with high absorption dissymmetry factor (g abs ) maxima of about 0.02, which is among the highest |g abs | values of helicenes in the visible range. These azulene‐embedded [ n ]helicenes contribute to the non‐benzenoid helicene library and allow the structure–property relationships to be better understood.