Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.296, 365-382, 1997
Highly-Oriented Bedo-TTF Molecules in Metallic Polymer Composites
Transport and optical. properties of the metallic reticulate-doped polymer composites based on bis(ethylenedioxy) tetrathiafulvalene (BEDO-TTF) complexes are investigated, and compared with the structural and physical properties of the respective bulk crystals. Exposing the surface of polycarbonate (PC) film containing the molecularly dispersed donor to the solvent/(iodine or bromine) vapor converted the donor into charge-transfer (CT) complexes, which dominate the conducting and thermoelectric properties of the composites. Both film surfaces doped with bromine and iodine are well conducting, showing metallic behavior down to low temperatures. A characteristic CT band for the highly conducting states of the partially oxidized BEDO-TTF molecules appeared in the infrared region. However, compared with the respective bulk crystal, absorptions of the intramolecular excitation of the donor molecules are greatly diminished for the incident Light perpendicular to the film surface. The PC film of (BEDO-TTF)-bromide exhibited high transparency for the visible Light, in contrast with the film of (BEDO-TTF)-iodide which showed intense absorptions due to the intramolecular excitation of the I-3(-) molecule in the visible region. Optical absorption spectra are anisotropic, which evidences the highly oriented BEDO-TTF molecules in the films. The molecular orientation was discussed in relation to the high conductivity and transparency. The crystal structure was also determined for newly obtained (BEDO-TTF)(2)Br(H2O)(3), the band structure calculation of which showed two-dimensional nature.