Azulene‐Embedded [n]Helicenes (n=5, 6 and 7)

Abstract

AbstractAzulene 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 (S1), small optical energy gap and anti‐Kasha emission. [6]‐, and [7]AzHs exhibit strong chiroptical responses with high absorption dissymmetry factor (gabs) maxima of about 0.02, which is among the highest |gabs| 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.