My thesis relates to the investigation of the ultrafast molecular dynamics involved in the photophysics/ photochemistry of different chemical systems in the gas, mesoscopic and liquid phases, with the element, site, and orbital specificity offered by time-resolved X-ray absorption spectroscopy, which is achieved with a table-top HHG source covering the water window that is combined with liquid flatjet delivery systems capable of delivering submicron thin sheets of liquid samples. These studies are made with the main goal of achieving a better understanding of the effect of the solvent or liquid environment on condensed systems. To that end, different molecular dynamics on the femto- to picosecond timescales have been successfully observed between the gaseous and condensed phases of different systems.