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

An overview over different theoretical approaches to study the aromaticity of porphyrins and porphyrin based compounds with the focus on magnetically induced current densities will be given.[1-3] The current densities presented are obtained with the gauge including magnetically induced current density method (GIMIC).[4] GIMIC is an independent and free available program that is used for the calculation of magnetically induced current densities using London orbitals.[5] 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.[2,6] 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.[7] 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 highlighted and discussed.[8,9] REFERENCES 1. H. Fliegl, R. R. Valiev, F. Pichierri and D. Sundholm, SPR Chemical Modelling series (doi: 10.1039/1472- 0973), Vol. 14, in press (2018) 2. D. Sundholm, H. Fliegl and R. J. F. Berger, WIREs Comput. Mol. Sci., 6, 639, (2016) 3. H. Fliegl, J. Jusélius and D. Sundholm, J. Phys. Chem. A, 120, 5658, (2016) 4. J. Jusélius, D. Sundholm and J. Gauss, J. Chem. Phys., 121, 3952, (2004) 5. Free download at: https://github.com/qmcurrents/gimic 6. C. Kumar, H. Fliegl and D. Sundholm, J. Phys. Chem. A, 121, 7282, (2017) 7. I. Benkyi, H. Fliegl, R. Valiev and D. Sundholm, Phys. Chem. Chem. Phys., 18, 11932, (2016) 8. R. R. Valiev, H. Fliegl and D. Sundholm, Chem. Comm., 53, 9866, (2017) 9. R. R. Valiev, H. Fliegl and D. Sundholm, Phys. Chem. Chem. Phys. 19, 25979, (2017)