CONCENTRATION-DEPENDENCE OF THE ELECTROOPTICAL SPECTRA FROM 2-DIMENSIONAL AGGREGATED CHROMOPHORE SYSTEMS

The linear and the quadratic Stark effects have been employed to characterize aggregate formation of an amphiphilic cyanine dye mixed with arachidic acid in various concentrations within Langmuir-Blodgett multilayers. Two different electrode configurations with the electric field directions parallel and normal to the films have been employed to test the responses of the electronic spectra to external fields. The observations have been used to quantify the induced and static dipole moment changes on excitation of the chromophores. A comparison of the results obtained from different multilayer arrangements is suggestive of inter-layer couplings for the case of head-to-head configurations of the aggregated chromophores. The results from the mixing studies reveal the evolution of two different aggregated species, one shifted hypsochromically and one shifted bathochromically from the monomer absorption and serve to quantify the relative proportions and sizes of these aggregates.