Molecular orientation of Ru(II) complexes introduced in hybrid Langmuir–Schaefer films of clay nanosheets and alkylammonium cations

Abstract

Ternary component hybrid films of amphiphilic alkylammonium cations, clay nanosheets, and ruthenium(II) complex cations were prepared by the modified Langmuir–Schaefer method. When a solution of the amphiphilic ammonium salt (octadecylammonium chloride, ODAH+Cl−) was spread at an air–clay dispersion interface, the clay nanosheets in the dispersion were adsorbed on the floating molecular film of ODAH+ by the electrostatic interaction. Then the floating film of ODAH+ and the clay was deposited on a glass plate and immersed in an aqueous solution of [RuL3]Cl2 (L=2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (dmphen), and 4,7-diphenyl-1,10-phenanthroline (dpp)) to form a ternary component hybrid monolayer. By repeating these procedures, a hybrid multilayer was fabricated. Characterization of the hybrid multilayers was carried out by electronic and IR spectral measurements and X-ray diffraction (XRD) method. Areas per [RuL3]2+ estimated from the analysis of the electronic spectra suggested that the Ru(II) complex cations interacted with each other through hydrophobic interaction. IR and XRD data indicated disordered alkylchains of ODAH+ which would occupy spaces between the [RuL3]2+ cations in the film. The tilt angles of 3-fold axes of [RuL3]2+ were determined to be 32–35° by analyzing electronic spectra measured with p- and s-polarized beams. An orientation model of the [RuL3]2+ cations in the film was proposed, in which substitution groups at 4- or 5-positions of 1,10-phenanthroline ligand were in contact with the clay nanosheet layers. It was likely that the sizes of the ligands and the interaction between the ligands affected the structure of the hybrid film.