Second harmonic generation from Langmuir-Blodgett monolayers of amphiphilic ruthenium(II) complexes: structural characterization with polarization measurements

Structural characterization for Lungmuir-Blodgett (LB) monolayer assemblies of two types of ruthenium(II) complexes were carried out by using the technique of surface second harmonic generation (SHG). Amphiphilic tris(2,2′-bipyridine)-type complexes, RuBipyCnB, and bis(1,10-phenanthroline)(2,2′-bipyridine)-type complexes, RuPhenCnB (n = 16,18), formed Z-type LB monolayers. The angular dependence of polarized second harmonic lights of these complexes was carefully examined. All complexes had similar hyperpolarizabilities. Average tilt angles of the polarization axes varied slightly but definitely on going from RuBipyCnB (38 ± 0.6°) to RuPhenCnB (35 ± 1.3°), which may be ascrible to structural difference in the chelating ligands of the complex. The polarization axes of the complexes were statistically distributed as to the azimuthal direction in the substrate surface.