Self-assembled monolayers (SAMs) of functional Ru I I complexes on optically transparent ultrathin Pt films (10-nm nominal thicknesses) have been prepared. We have demonstrated that reversible Ru I I I / I I redox switching of these SAMs can be achieved by using appropriate oxidizing or reducing agents. Such a switching in molecular properties has been simply detected by transmission spectroscopy with a conventional spectrophotometer following the appearance/disappearance of the optical absorption metal-to-ligand charge-transfer (MLCT) band in the visible region. In light of their potential multifunctional properties, these SAMs on an optically transparent metal electrode are appealing candidates in the perspective of integrated molecular switch nanodevices.