Synthesis of a Tetrabenzotetraaza[8]circulene by a Fold-In Oxidative Fusion Reaction

Tetrabenzotetraaza[8]circulene (1) has been synthesized in good yield by a fold-in oxidative fusion reaction of a 1,2-phenylene-bridged cyclic tetrapyrrole. X-ray diffraction analysis of 1 has revealed a planar square structure with a central cyclooctatetraene (COT) core that shows little alternation of the bond lengths. Despite these structural features, 1 shows aromatic-like character, such as sharp absorption bands, high fluorescence quantum yields (phi(F)=0.55 in THF), and a single exponential fluorescence decay with (F)=3.8ns. These observations indicate a dominant contribution of an [8]radialene-like conjugation and hence aromatic character of the local aromatic segments in 1.