B,N‐Embedded Helical Nanographenes Showing an Ion‐Triggered Chiroptical Switching Function

Intramolecular aromatic oxidative coupling of 3,6‐bis(m‐terphenyl‐2’‐yl)carbazole provided a bis(m‐terphenyl)‐fused carbazole, while that of 3,6‐bis(m‐terphenyl‐2’‐yl)‐1,8‐diphenylcarbazole afforded a bis(quaterphenyl)‐fused carbazole. Borylation of the latter furnished a B,N‐embedded helical nanographene binding a fluoride anion via a structural change from the three‐coordinate boron to the four‐coordinate boron. The anionic charge derived from the fluoride anion is stabilized over the expanded p‐framework, which leads to the high binding constant (Ka) of 1 × 105 M–1. The four‐coordinate boron species was converted back to the parent three‐coordinate boron species with Ag+, and the chiroptical switch between the three‐coordinate boron and four‐coordinate boron species has been achieved via the ion recognition with the change in the color and glum values.