We report the synthesis of a functional molecule, a quatertiophene-based surfactant, which can both adsorb at the water/gas interface (surface active molecule) and aggregate through π−π stacking interactions. We assess then the ability of this molecule to create these functionalities at interfaces. This interfacial functional aggregation, characterized here in situ for the first time, is probed thanks to Langmuir trough experiments and spectrometric ellipsometry. These results pave the way to the design of new water based optoelectronic devices.