Sequential N-Alkylations of Tetrabenzotetraaza[8]circulene as a Tool To Tune Its Optical Properties.

Sequential N-alkylations of tetrabenzotetraaza[8]circulene 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 [8]circulenes have been also prepared.