HIGHLY-ORIENTED BEDO-TTF MOLECULES IN METALLIC POLYMER COMPOSITES

Transport and optical. properties of the metallic reticulate-doped pol ymer composites based on bis(ethylenedioxy) tetrathiafulvalene (BEDO-T TF) complexes are investigated, and compared with the structural and p hysical properties of the respective bulk crystals. Exposing the surfa ce of polycarbonate (PC) film containing the molecularly dispersed don or to the solvent/(iodine or bromine) vapor converted the donor into c harge-transfer (CT) complexes, which dominate the conducting and therm oelectric 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 conducti ng 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 ar e 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 spec tra are anisotropic, which evidences the highly oriented BEDO-TTF mole cules in the films. The molecular orientation was discussed in relatio n 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.