This doctoral thesis describes the application of a combination of Density Functional Theory (DFT) methods and kinetic models to elucidate the mechanism of light-driven synthesis reactions in solution. The aforementioned strategy is applied to study two types of reactions of commercial interest. In the first part, the mechanism of chemical transformations directly activated by visible light is analyzed. On the other hand, the second part covers reactions in which light activation takes place via a photocatalyst. For both cases, experimental outcomes and properties such as selectivity and quantum yield were correctly reproduced and rationalized, on the basis of the electronic structure properties that define the systems involved. In addition, kinetic models proved vital in the computation of mechanistic aspects of photo-induced transformations as mere comparisons of energy barriers fail to account for large differences in concentration present.