0000000000589748
AUTHOR
Georg Grewer
Photoelectropoling of azobenzene chromophores in molecular films
The photoinduced reorientation and photoelectropoling processes were investigated in molecular films of aliphatically substituted azobenzenes. While polarized illumination leads to a conversion of isotropic samples into anisotropic ones, upon application of external electric fields even macroscopically polar materials are created. The macroscopic polarity can be reversed under suitable experimental conditions. Order parameters as a function of the poling field were determined by Stark spectroscopy. Using atomic force microscopy it is shown that the structure of the sample is well defined on a microscopic length scale, whereas on a macroscopic length scale it is not.
Electro-optical spectroscopy on aggregated chromophore systems in Langmuir-Blodgett films
Linear and quadratic Stark spectra were measured on LB films that contained a hydrophobically substituted cyanine chromophore in binary mixtures with arachidic acid. The external field was applied normal or parallel to the film surface on samples with different internal symmetry. It was found that the orientation of the symmetry axis of the dye molecule is close to the surface normal. A significant number of molecules, 5–10%, are flipped head-to-tail from the main orientation. Parallel to the film surface, large polarizability changes on electronic excitation, Δα ∼ 1000 A3, were observed that reflect electron delocalization over aggregates. At low dye concentrations, large internal electric…
Concentration dependence of the electro-optical spectra from two-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 t…