This thesis introduces the basic principles of quantum chemistry, photochemistry and the computation of molecular properties. The results of original research are divided in three parts. Each part is constructed around a common feature of those projects, including a specific theoretical introduction. The first part approaches the problem of modelling solvent effects for property calculations. It approaches more specifically the use of continuum models and frozen density embedding methods. The second part highlights the problem of computing charge transfer excitations. It starts with a short presentation of the failure of linear-response time-dependent density functional theory and is followed by the results of two projects involving the computation of charge-transfer like excitations. Finally, the last part approaches the case where multireference methods are necessary to compute properly the features of different potential energy surfaces.