MESOGENIC PYRROLE DERIVATIVES IN LANGMUIR-BLODGETT-FILMS

A pyrrole monomer linked through a spacer of various lengths (0, 3, or 8 carbons) to a mesogenic core has been studied in Langmuir and Langmuir-Blodgett (LB) films. Pure monolayers of these mesogenic pyrrole derivatives have been transferred onto solid substrates, leading to highly ordered built-up films. The spacer between the mesogenic core and the pyrrole moiety has clearly no influence on the organization of these molecules in the LB films. These multilayers can be easily polymerized and oxidized by iodine vapors. As shown by GPC analysis, the obtained polymers have a variable molecular weight depending on the spacer length, Alternated layers of one of these pyrrole derivatives and 1-monostearoyl-rac-glycerol lead to similar results for the polymerization, suggesting that this reaction occurs mainly in each monolayer and not between two successive layers. Conductivity of the obtained material is highly anisotropic: about 10(-1)-10(-2) S.cm(-1) for the in-plane conductivity and less than 10(-8) S.cm(-1) for the conductivity across the film. No correlation has been found between the conductivity of the LB films and the length of the polymers: conductivity of such material is then mainly Limited by defects in the LB films and poor conductivity between molecules.