Global Aromatic\nRing Currents in Neutral Porphyrin\nNanobelts

The ability of a\nring-shaped molecule to sustain a global\naromatic\nor antiaromatic ring current when placed in a magnetic field indicates\nthat its electronic wave function is coherently delocalized around\nits whole circumference. Large molecules that display this behavior\nare attractive components for molecular electronic devices, but this\nphenomenon is rare in neutral molecules with circuits of more than\n40 π-electrons. Here, we use theoretical methods to investigate\nhow the global ring currents evolve with increasing ring size in cyclic\nmolecular nanobelts built from edge-fused porphyrins. Our results\nindicate that a global ring current persists in neutral nanobelts\nwith Hückel circuits of 220 π-electrons (22 porphyrin\nunits, circumference 18.6 nm). Our predictions are validated by using\ncoupled clusters to construct a density functional approximation (denoted\nas OX-B3LYP) that accurately describes these nanobelts and by checking\ncompliance with Koopmans’ theorem.