Molecular Orientation in Langmuir Monolayers Containing the [M(dmit)2]n-Anion Determined from Surface Pressure and Surface Potential Isotherms

Abstract

The behavior of three dmit containing semiamphiphilic salts ([Ni(dmit)2][DDI]2, [Ni(dmit)2][DDI], [Pd(dmit)2][DDI]2) has been investigated in detail at the air−water interface. An osmotic equation of state was fitted to the liquid expanded regions of the π−A isotherms, while the surface potential isotherms were analyzed using the Helmholtz equation (HE). A molecular orientation was proposed for each material based on the cross-sectional areas calculated from the equation of state, and these were consistent with the apparent dipole moments calculated from the HE. The behavior of the palladium salt was found to differ from that of the two nickel salts, with plots of isotherm gradient against water content being coincident for the nickel salts but not so for the palladium containing material. This was explained as being due to the almost identical lipid−lipid Lucassen−Reynders (LR) interaction coefficients calculated for the two nickel salts, which differed significantly from the coefficient calculated for t...