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-aggregat ion in supported Langmuir-Blodgett (LB) monolayers. The spectral prope rties 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 f rom the LB films formed by alkyl-substituted stilbene fatty acids, sug gests that H-aggregation is a minimum free energy packing assembly for stilbene units in LB films. Beta-stilbene methylation prevents the mo lecules from tight packing and produces a pronounced perturbation on t he H-aggregate absorbance spectrum.