Polarized ATR-IR studies of surface-field-induced anchoring of alkyl cyanobiphenyls

We report initial studies of the use of polarized ATR-IR spectroscopy to obtain information on molecular alignment, on the mesoscopic scale, in the interfacial region of alkyl cyanobiphenyl liquid crystals in contact with self-assembled monolayers (SAMs). Specific mesoscopic alignment was induced by variation of the surface field, via the omega-functional group of self-assembled monolayers of alkanethiol derivatives. Our experimental approach involved the deposition of a thin gold layer onto a ZnSe prism. The presence of this layer strongly attenuates the s-polarized field leading to an "effective surface selection rule", which can be used to determine the average orientation of the liquid crystal molecules within the attenuation depth of the evanescent field. A frequency shift of the C=N stretching band was seen in the case of homeotropic anchoring.