Magnetically Induced Current Densities in Zinc Porphyrin Nanoshells.

The molecular structures of porphyrinoid cages were obtained by constructing small polyhedral graphs whose vertices have degree-4. The initial structures were then fully optimized at the density functional theory (DFT) level using the generalized gradient approximation. Some of polyhedral vertices were replaced with Zn-porphyrin units and their edges were replaced with ethyne or butadiyne bridges or connected by fusing two neighboring Zn-porphyrin units. Molecule is an ethyne-bridge porphyrinoid nanotube, whose ends are sealed with a Zn-porphyrin. Molecule is the corresponding open porphyrinoid nanotube. Molecule is a clam-like porphyrinoid cage, whose shells consist of fused Zn-porphyrins, and the two halves are connected via butadiyne bridges. Molecule is a cross-belt of fused Zn-porphyrins, and molecule is a cross-belt of Zn-porphyrins connected with butadiyne bridges. The magnetically induced current density of the optimized porphyrinoid cages was calculated for determining the aromatic character, the degree of aromaticity and the current-density pathways. The current-density calculations were performed at the DFT level with the gauge─including magnetically induced currents (GIMIC) method using the B3LYP hybrid functional and def2-SVP basis sets. Calculations of the current densities show that molecule sustains a paratropic ring current around the nanotube, whereas sealing the ends as in molecule leads to an almost nonaromatic nanotube. Fusing porphyrinoids as in molecules and results in complicated current-density pathways that differ from the ones usually appearing in porphyrinoids. The aromatic character of molecules and changes upon oxidation. The neutral molecule is antiaromatic, whereas the dication is nonaromatic. Molecule is nonaromatic, and its dication is aromatic.