Following our synthetic papers on the the synthesis of porphyrin N‑ and dithiaporphyrin S‑oxides (Banerjee, S.; Zeller, M.; Brückner, C. ‘MTO/H2O2/Pyrazole-Mediated N-Oxidation of meso-Tetraarylporphyrins and –chlorins, and S-Oxidation of meso-Tetraaryldithiaporphyrin and ‑chlorin’ J. Org. Chem. 2009, 74, 4283–4288.), this theoretical paper illuminates the origin of the optical properties of these compounds. Bruhn, T.; Brückner, C. ‘Origin of the Absorption Spectra of Porphyrin N‑ and Dithiaporphyrin S‑Oxides in their Neutral and Protonated States’ Phys. Chem. Chem. Phys. 2015, 17, 3560–3569. DOI: 10.1039/c4cp04675g