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.

中文翻译：

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部分熔合的 12-卟啉纳米环中的电荷离域和全局芳香性


芳香族和反芳香族环流可以揭示π共轭大环周围的整体电子离域，尽管这些现象在大环中知之甚少。在这里，我们提出了完全π偶联的环卟啉 12-mer 的模板定向合成，该二聚体由六个丁二炔桥连接的 6 个 β，中旋，β 边熔合卟啉二聚体组成。这个部分熔融纳米环的最低能量 π-π∗ 吸收带向 NIR 中移动得很远，证实了大环圆周周围的强 π 共轭。通过 1H 和 19F NMR 波谱对氧化和还原的纳米环-模板复合物的研究表明存在相干的全局（反）芳香环电流，这与 DFT 计算一致。更强的 π 共轭即使在低水平的氧化或还原下也能实现全局电荷离域。这些发现为环状分子线的工程设计开辟了新的途径。