The Langmuir monolayer behavior of (di)alkoxy-substituted precursor poly(p-phenylenevinylenes) (PPVs) with a methoxy-leaving group was studied. The average orientation of the aromatic ring and the ether groups at the air-water interface was elucidated by external FT-infrared reflection spectroscopy measurements at the air-water interface combined with FT-IR computer simulations. The aromatic rings of the precursors, except those of the dibutoxy-substituted one, take on, directly after spreading, an almost perpendicular orientation to the water subphase. The isotherms of these precursors showed no special transitions, and these polymers can be considered to be in a condensed or 2-D collapsed state with lateral cohesive π-π interactions between the aromatic rings as the most prominent interaction leading to this condensed state. The aromatic rings of the dibutoxy-substituted precursor are lying flat at the water surface at large areas per repeating unit and can be considered to be in the expanded state directly after spreading. The isotherm of this precursor showed two transitions because here the chain conformation is predominantly determined by the butyl chains and not by the main chain.

Floating monolayers as well as Langmuir-Blodgett (LB) films of poly(isocyanide)s containing NLO-active side chains appear to be capable of generating second-harmonic light. Spin-coated films and cast films of these polymers do not shown this behavior. These results indicate that the NLO activity of the LB films originates from the orientation of the side chains obtained at the air-water interface. In the case of poly(isocyanide)s with relatively hydrophobic side chains the second-harmonic intensities generated from the LB films are small, probably because the films are of the Y-type. Poly(isocyanide)s with more hydrophilic side chains form LB films which are Z-type. These films show stable secondharmonic generation without the need of poling with high electrical fields at high temperatures.

Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractThe properties and structure of Langmuir-Blodgett mono-and multilayers of several poly(isocyanide)s with non-linear optically active side-chains were studied. These polymers formed very rigid layers or layers which appeared to be unstable. To circumvent this problem they were mixed with other poly(isocyanide)s or with amylose-butyrate. Transmission electron microscopy studies of the polymeric mixtures revealed that phase separation occurred in all cases and that only poly(isocyanide)s substituted with hydrophilic side chains formed monomolecular layers. Depending on the nature of the polymer which was used for mixing, the dye polymers could be deposited with Y-or Z-type transfer. Second-harmonic intensities generated from these films were small in the case of the Y-type multilayered films and moderately high in the case of the Z-type films.

The Langmuir monolayer stability and transfer properties of (di)alkoxy-substituted precursor PPVs were studied. All polymers formed stable monolayers, but the packing of the monomeric units in the monolayer depended strongly on the substituents. The less closely packed monolayers can be transferred with the Langmuir-Blodgett technique, while the closely packed monolayers, with strong π-π interaction between the aromatic rings, can only be transferred with the Langmuir-Schaefer technique due to the stiffness of the monolayers. Transmission and grazing incidence reflection FT-IR spectroscopy in combination with IR spectra computer simulations revealed that in many instances the orientation of the precursor at the water interface is largely preserved after transfer of the monolayer. The roughness and the thickness of the multilayers were determined by small-angle X-ray reflection.

The dimethoxy-substituted precursor poly(p-phenylenevinylene) (prec-DMePPV) was partly converted to dimethoxy-PPV by exposing the precursor solution in chloroform to daylight. The monolayer and transfer behavior of this partly converted precursor (pc-DMePPV) was studied with the LangmuirBlodgett technique. In contrast to prec-DMePPV, an excellent transfer behavior was found for pc-DMePPV, and it was possible to build up multilayer films. The observed Z-type transfer behavior was peculiar, because the transfer ratio was higher than 1, and after deposition the monolayer expanded. Although the pc-DMePPV is not a rigid-rod-like polymer, an in-plane orientation of the chain in the transfer direction was found in the multilayers. We assume that, due to hydrophobic intra-and intermolecular interactions between the conjugated parts in the chains, the monolayer of pc-DMePPV can be considered as a 2D physical network, and the obtained orientation in the dipping direction is due to the stretching of this network during deposition. After each dip the monolayer relaxes, restoring the free volume again as observed by the expansion of the film. After full conversion to dimethoxy-PPV (DMePPV) by thermal treatment of the multilayer, the dipping-induced in-plane orientation was preserved.