Charge Delocalization and Global Aromaticity in a Partially Fused 12-Porphyrin Nanoring

Aromatic and antiaromatic ring currents can reveal global electronic delocalization around the circumference of pi-conjugated macrocycles, although these phenomena are poorly understood in large rings. Here we present the template-directed synthesis of a fully pi-conjugated cyclic porphyrin 12-mer consisting of six b,meso,b-edge-fused porphyrin dimers connected by six butadiyne bridges. The lowest energy pi-pi* absorption band of this partially fused nanoring is shifted far into the NIR, confirming the strong pi-conjugation around the circumference of the macrocycle. Investigation of the oxidized and reduced nanoring-template complex by 1H and 19F NMR spectroscopy demonstrates the presence of coherent global (anti)aromatic ring currents, consistent with DFT calculations. The stronger -conjugation enables global charge delocalization even at low levels of oxidation or reduction. These findings open new avenues for the engineering of cyclic molecular wires.