Sequential N-alkylations of tetrabenzotetraazacirculene provided mono-, di-, tri, and tetra-N-alkylated products in a controlled manner. Curiously, only opp isomer was obtained as a di-N-alkylated product. Upon increase of the N-alkyl groups, the absorption and emission spectra exhibit continuous red-shifts, and the excited-state lifetimes become shortened, probably because of increased steric congestion at the nitrogen atoms that causes the central core to deviate from planarity. Mixed N-substituted circulenes have been also prepared.
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The work at Kyoto was supported by Grants-in-Aid from JSPS KAKENHI Grant Numbers (25220822, 26810021 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). The authors thank Prof. Dr. Hiromitsu Maeda and Dr. Yuya Bando (Ritsumeikan University) for MALDI-TOF MS measurement.
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