Fluorescence Studies on Intermolecular Interactions of Cyanobiphenyl Groups Chemisorbed on a Quartz Surface with Liquid Crystals

Abstract

Fluorescence measurements were made of cyanobiphenyl (CB) residues covalently bound to a quartz plate through silylation to obtain information about molecular interactions between the fluorophore and solvent molecules as well as liquid crystal molecules at an interface. It was found that the fluorescence of surface-attached CB groups is quite different from that of corresponding solutions. A marked red shift was observed at the interface of a quartz plate and a nonpolar solvent like cyclohexane, reflecting a polar microenvironment surrounding the fluorophore residues owing to surface silanols and/or adsorbed water molecules, and a new fluorescent band possibly ascribable to an excimer of CB was also observed on the silica surface in cyclohexane. In contrast to these, the fluorescence from CB units bound on a quartz plate wetted with a nonpolar nematic liquid crystal showed that its red shift was much reduced and the emission band in the longer wavelength region was not observed. On the contrary, no alteration of the fluorescence of a pyrene photoprobe covalently attached to a silica surface was induced by contact with a nematic liquid crystal. These observations are reasonably interpreted as a result of specific molecular interactions between surface CB units and liquid crystal molecules on the interface.