Photocatalytic systems for complete h-WS in the absence of sacrificial reagents are based on materials or molecules or on a combination of both. However, the number of reported examples is very scarce, presenting very low efficiencies and sometimes are difficult to reproduce. In order to discover efficient systems, it is important to identify and understand the complex chemical reactions involved in the light-induced process coupled to chemical reactions. For this purpose, the light induced oxidation and reduction reactions can be studied independently using large amounts of sacrificial reagents. Molecular-based systems, in principle, offer the possibility of a better in-depth characterization of the kinetics and reaction intermediates involved than the systems based on materials.