Theoretical studies as a tool for understanding the aromatic character of porphyrinoid compounds

The present review gives an overview over different theoretical approaches to study the aromaticity of porphyrins and porphyrin based compounds with the focus on magnetically induced current densities including recent developments and applications in our groups. Observed trends as well as new visualization options for current densities are presented. It is shown that new insights can be obtained for porphyrin based compounds by complementing experimental work with computed current densities. A thorough current density analysis can lead to novel viewpoints and detailed interpretations of experimental findings as compared to many other approaches. Current density studies might also serve as inspiration for future experimental works. Merely a visual inspection of the current density might not be sufficient and should therefore always be accompanied by an integration analysis of the current flow, which yields accurate current-density pathways. Recent attempts to link calculated current strength susceptibilities of antiaromatic porphyrinoids to optical properties and magnetizabilities are discussed.