New Insights on Aromatic Pathways in Porphyrinoids

Abstract

Electronic and spectroscopic properties of porphyrinoid macrocycles are, to a large extent, determined by the number of π-electrons participating in the conjugation network. Full control of the number of π-electrons implies full control of the aromatic or antiaromatic character of the molecule. To achieve this, knowledge about the electron mobility pathways within a molecule is essential. Experimentally, these pathways are not easily accessible. Therefore theoretical studies are necessary to complement experiments that aim at systematically synthesizing porphyrinoids with distinct properties. A possible way to achieve this is the systematic investigation of magnetically induced current densities to determine reliable aromatic pathways in molecules.[1] In my talk I will present an overview of different ways to systematically calculate and analyze the magnetically induced current density in porphyrin based molecules. The computational approach used in my group is the gauge including magnetically induced current density method (GIMIC).[2,3] GIMIC is a independent program that is used for the calculation of magnetically induced current densities using London orbitals.[2, 3] Numerical integration of the current flow around molecular rings and along selected chemical bonds can be used for determining current pathways and the degree of aromaticity of various molecules according to the magnetic criterion.[4,5] A new feature of the GIMIC program is the calculation of the anisotropy of the magnetically induced density using gauge including atomic orbitals.[6] Very recent results obtained for various porphyrinoid molecules will be highlighted illustrating the potential and challenges of the method.[7-9]