In-Situ Second-Harmonic Generation and Luminescence Measurements for Structural Characterization of Ruthenium−Polypyridine Complex Monolayers with Two and Four Aliphatic Tails at the Air/Water Interface

Abstract

Langmuir monolayer assemblies of ruthenium−polypyridine complexes having two and four aliphatic tails were studied by in-situ optical second-harmonic generation (SHG) and luminescence measurements, together with surface pressure−molecular area (π−Α) isotherms. As the monolayer was compressed, the four-tailed complex showed a distinct phase transition at a 30−40 mN/m region from phase I (1.3 nm2 mean molecular area) to phase II (1.1 nm2). Excitation with 1064-nm light gave an SHG signal at 532 nm that appeared almost synchronously with the increase of surface pressure, but the p-polarized component of the SHG signal, induced by either p- (parallel to the plane of incidence) or s- (perpendicular to the plane of incidence) polarized fundamental light, showed a different profile upon compression of the monolayer. In the phase II region, the p-polarized component increased steeply, whereas the s-polarized component decreased to almost zero. A significant blue-shift and a longer lifetime of the luminescence sig...