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. Decorating the circle: Controlled N‐butylation of tetrabenzotetraaza[8]circulene afforded mono‐, di‐, tri‐, and tetra‐N‐butylated derivatives. N‐Benzylation of dibutylated and tributylated products provided mixed tetra‐N‐alkylated [8]circulenes (see figure). These novel aza[8]circulenes exhibit slightly but distinctly perturbed UV/Vis absorption, emission, and excited‐state dynamics owing to the structural deformation induced by the N‐substituents.