Hideaki MONJUSHIRO, Kazumasa HARADA, Miho NAKAURA, Noriaki KATO, Masa-aki HAGA, Matthew RYAN (York Univ.) and A. B. P. LEVER (York Univ.)
[Mol. Cryst. Liq. Cryst. 294, 15 (1997)]
In order to study the controlled ordering of the metal complex in two dimensions, we have synthesized new surfactant ruthenium complexes containing 6,6'-bis(N-octyl- or laurylbenzimidazolyl)-2,2'-bipyridine(L = L8 or L12) by the reaction of [RuCl2((eta)6-(pi)-cymene)]2 with L in methanol and DMSO. The Ru complexes formed a stable monolayer film on the Langmuir trough air-water interface. The isotherm indicates the complex begins to pack into the expanded state at an area/molecule of approximately 110 Å/molecule. As compression continues, a plateau region occurs at 20.5 mNm-1. The isotherm then becomes steeper with a limiting molecular area of about 52 Å/molecule and a collapse pressure of 42 mNm-1. This behavior suggests that at low surface pressure the plane of the complex are lying flat on the surface with the alkyl chains protruding away from the surface. At higher pressure, the complex is packed and oriented almost perpendicular to the surface. In the LB monolayer films, the signals for cyano groups were split into two peaks with equal height at 397.0 and 397.9 eV, even the N1s peaks on tetradentate ligand remain identical, which is distinct from those for the powder sample. This spectral difference indicates that the complex is oriented almost perpendicular to the surface and two cyano groups possess different chemical environments; i.e., one of axial cyano groups will be weakly interacted to the surface, probably to the hydroxy group on the glass surface through hydrogen bonding. This XPS results are consistent with the hypsochromic spectral shift on the UV spectra.
Scheme 1. Structure of Ru complexes
Figure 1. XPS N1s spectra of trans-Ru(CN)2(L12) for both the powders and LB films on glass plate.