||Polycyclic aromatic hydrocarbons (PAHs) are the most abundant class of organic compounds in space. The PAH field evolves from the constant interaction between experimentalists, theorists, modellers and observers. While laboratory research and quantum chemical calculations together set up the molecular properties of PAH species, astronomers on the other hand, retrieve as much information as possible from the space observations. Nowadays, the PAH field is advanced enough to start implementing all these results into astronomical models, in order to study PAHs from a molecular groundwork. In this regard, the research projects presented in this thesis do precisely that. They constitute a first attempt to gather the vast current knowledge available on specific PAH molecules (not using generic properties), and put it in an astrophysical context, and with it, target some of the key subjects of the field such as: the existence of the so-called grandPAHs in space; the role of PAHs in the formation of molecular hydrogen in photodissociation regions; the abundance of superhydrogenated PAHs and their contribution as a carrier of the 3.4 micron band observed in photodissociation regions; and the deuterium fractionation in PAHs, and their consequent role in explaining the observed deuterium abundance in the local interstellar medium.