Aggregation Phenomena in Langmuir-Blodgett Films of Polar Stilbene Amphiphiles

The effect of incorporating polar-substituted stilbene groups into two-dimensional molecular assemblies was studied. A homologous series of stilbene-containing hexadecanoic acids was found to exhibit H-aggregation in supported Langmuir-Blodgett (LB) monolayers. The spectral properties of these aggregates are insensitive to the particular homologue used, either alone or in 1:1 mixtures. This result, particularly when considered in the context of its extreme similarity to that obtained from the LB films formed by alkyl-substituted stilbene fatty acids, suggests that H-aggregation is a minimum free energy packing assembly for stilbene units in LB films. β-Stilbene methylation prevents the molecules from tight packing and produces a pronounced perturbation on the H-aggregate absorbance spectrum.