Oxidative fusion reactions of ortho-phenylene-bridged cyclic hexapyrroles and hexathiophenes furnished novel closed helicenes in a selective manner. X-Ray diffraction analysis unambiguously revealed the structures to be a closed pentaazahelicene, the longest azahelicene reported so far, and an unexpected double-helical structure of hexathia/helicene, whose formation was assumed to result from multiple oxidative fusion along with a 1,2-aryl shift. The pentaazahelicene exhibited well-defined emission with high fluorescence quantum yield (ΦF=0.31) among the known helicenes. Chiral resolution of the racemic pentaazahelicene and hexathia/helicene were achieved by chiral-phase HPLC and the enantiomers were characterized by circular dichroism spectra and DFT calculations.
Bibliographical noteFunding Information:
The work at Kyoto was supported by JSPS KAKENHI (grant numbers JP25220802, JP16K13952, JP26810021, and JP16H00909). The work at Yonsei was supported by the Global Research Laboratory (GRL) Program funded by the Ministry of Science, ICT & Future, Korea (2013K1A1A2A02050183). T.M. thanks the JSPS KAKENHI (Grant Numbers JP15H03779, JP15K13642, JP16KK0111, JP17H05261), Asahi Glass Foundation, and Cosmetology Research Foundation for financial support. The authors thank Prof. Dr. Hiromitsu Maeda and Dr. Yohei Haketa (Ritsu-meikan University) for MALDI-TOF MS measurement.
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