The research mainly concerns with the study of simple molecular systems under pressure, using the Diamond Anvil Cell (DAC) technique to compress the samples under equilibrium conditions up to 10⁶ bar. These studies are useful to understand fundamental physical and chemical properties of matter and to simulate pressure and temperature conditions occurring in nature, as for example in the Earth interior or in other astrophysical systems. Photochemical effects act at high pressure as a further effective regulatory tool of the reaction mechanism, because the electronic distribution, and thus the molecular geometry, can be modified by a suitable optical excitation. The possibility to appropriately and simultaneously control pressure, temperature and electronic excitation opens new perspectives in solid state chemistry, for example towards a synthesis of materials of technological interest by using only physical methods.