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 π-conjugated macrocycles, although these phenomena are poorly understood in large rings. Here, we present the template-directed synthesis of a fully π-conjugated cyclic porphyrin 12-mer consisting of six β,meso,β-edge-fused porphyrin dimers connected by six butadiyne bridges. The lowest energy π-π∗ absorption band of this partially fused nanoring is shifted far into the NIR, confirming strong π-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 π-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.