HIGHLY ORDERED LB FILMS OF DHAP - A DONOR-ACCEPTOR-SUBSTITUTED POLYENE

The donor acceptor substituted polyene 4-dihexadecylaminophenyl)-2-met hyl-2,4-pentadienal (DHAP) is-due to its amphiphilic nature-a promisin g candidate for the Langmuir-Blodgett (LB) technique. The molecule was studied as a monolayer on a pure water surface under argon atmosphere . Monolayers and multilayers were transferred onto solid support. The films showed a high degree of order in the monolayer as well as in thi ck multilayers. LB films were investigated with polarisation dependent UV/VIS absorption spectroscopy. The film spectra showed additional ab sorption peaks which were not present in the spectra of the molecules in solution. The relative peak intensities were highly dependent on th e orientation of the electric field vector with respect to the substra te normal. To get a detailed picture of the arrangement of the films o n the molecular level, we studied the polarisation dependence of the F TIR spectra in different experimental set-ups. The spectra showed a pe rpendicular orientation of the conjugated system with respect to the s ubstrate, whereas the backbone of the saturated hydrocarbon chains sho wed a medium tilt angle of 20.0-degrees with respect to the substrate normal. X-ray small angle diffraction measurements were applied to inv estigate the thickness of the LB layers. From the position of the Brag g peaks, a thickness of 5.45 nm per bilayer can be calculated, in agre ement with a bilayer model showing different molecular alignment of th e molecules transferred during upstroke and downstroke.