Karl Michael Ziems investigates a meso-mesityl-2,6-Iodine substituted Boron Dipyrromethene (BODIPY) dye regarding its functionality as photosensitizer in a two-component light-driven hydrogen evolution. The author uses quantum chemical calculations performed at the time-dependent density functional (TDDFT) and multi-state restricted active space perturbation theory through second-order (MS-RASPT2) level of theory. The light-induced processes associated with the formation of the active photosensitizer, i.e., by means of charge separation, as well as the population of undesired degradative pathways are elucidated. Hereby, the two proposed and investigated mechanisms are based on a heavy atom effect of iodine in the (excited) singlet/triplet manifold and preliminary reduction (of the dye) by a sacrificial electron donor and subsequent photoexcitation.