Tunable Synthesis of Multi‐Responsive NH‐Containing Helical Nanographenes With a Chiroptical Switching Function

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Abstract
Helical nanographenes (HNGs) have attracted much attention owing to their red‐region chiroptical properties. These HNGs, typically based on hexa‐peri‐hexabenzocoronene (HBC), are commonly synthesized via the Diels–Alder reaction followed by the Scholl reaction; however, the former generally requires harsh conditions (> 200°C), thereby limiting modular tuning and structural diversity. Here, we report the tunable synthesis of NH‐containing HNGs based on carbazole frameworks that enable π‐extension without protecting the NH group. Multifold Scholl reactions of 1,3,6,8‐tetrakis(oligophenyl)‐appended carbazoles, derived from a common 1,3,6,8‐tetrabromocarbazole platform, enabling uniform installation of arene units for π‐extension, afford HNGs through the formation of up to 12 C─C bonds at defined positions. The use of identical arenes suppresses regioisomer formation, while the symmetric framework enforces a single reaction pathway, avoiding regioisomeric scrambling. The resulting HNGs were successfully resolved into their enantiopure forms by chiral HPLC and exhibit distinct chiroptical properties. Notably, the unprotected NH groups enable a pronounced redshift and reversible on/off switching of circularly polarized luminescence (CPL) upon treatment with base and acid, respectively, indicating pH‐driven chiroptical switching. Furthermore, excited‐state proton transfer in dimethyl sulfoxide generates anionic species showing redshifted fluorescence and CPL even under neutral conditions.
Funding Information
  • Japan Society for the Promotion of Science (JPJS00420230010)
  • Japan Society for the Promotion of Science (24K08395)
  • Japan Society for the Promotion of Science (24H00005)
  • Japan Society for the Promotion of Science (21K05039)

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