Liquid interfaces, which are boundaries between two isotropic media, hold pivotal importance across various scientific disciplines. Despite their significance, studying these interfaces presents a notable challenge due to their ’buried’ nature. This thesis primarily focuses on enhancing our understanding of liquid/liquid interfaces, bene- fiting from the unique capabilities of Surface Second Harmonic Generation (SSHG). Owing to the cancellation of the SHG process in centrosymmetric media like bulk liquids, the signal originates only from the interface region where the symmetry is broken, making SSHG a robust tool for investigating surface properties and dynam- ics on an ultrafast timescale.

This work has two main objectives: firstly, we use molecular probes to elucidate various interfacial properties such as charge, friction, and aggregation. Secondly, we strive to understand how these interfacial properties impact chemical reactivity.

Key studies within this work include investigating the effects of room-temperature ionic liquids on the adsorption of a cationic probe at the dodecane/water interface, examining the impact of confinement on the isomerization dynamics of an azoben- zene dye, namely methyl orange, and exploring the excited-state properties of a por- phyrin–fullerene dyad and its porphyrin analogue at the dodecane/water interface.

The findings from these investigations enhance our growing understanding of liquid interfaces, offering valuable insights.