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 Langm uir-Blodgett (LB) films. Pure monolayers of these mesogenic pyrrole de rivatives have been transferred onto solid substrates, leading to high ly ordered built-up films. The spacer between the mesogenic core and t he pyrrole moiety has clearly no influence on the organization of thes e molecules in the LB films. These multilayers can be easily polymeriz ed and oxidized by iodine vapors. As shown by GPC analysis, the obtain ed polymers have a variable molecular weight depending on the spacer l ength, Alternated layers of one of these pyrrole derivatives and 1-mon ostearoyl-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 c onductivity and less than 10(-8) S.cm(-1) for the conductivity across the film. No correlation has been found between the conductivity of th e LB films and the length of the polymers: conductivity of such materi al is then mainly Limited by defects in the LB films and poor conducti vity between molecules.