Physical properties of mixed Langmuir-Blodgett conducting films based on a tetrathiafulvalene derivative
- Centre de Recherche Paul Pascal, Pessac (France)
Electroactive molecules such as (ethylenedithio) bis(octadecylthio)tetrathiafulvalence [EDTTTF(SC{sub 18}){sub 2}] are useful molecular blocks for building up Langmuir-Blodgett conducting films when they are mixed with a fatty acid such as behenic acid and then doped with iodine vapors. To understand the molecular organization in these layers, the authors have investigated the IR electronic and vibrational absorption spectra, the resonance Raman scattering of the iodine species and the dc electrical conductivity as a function of the fatty acid content, and the number of deposited layers. These investigations have led the authors to propose a model of heterogeneous mixed film where clusters of EDTTTF(SC{sub 18}){sub 2} are surrounded by fatty acids bilayers, as demonstrated by using a 3D percolation theory. Inside a conducting cluster, the authors have shown that the iodine intercalation process occurs in two stages: The insertion process lends to a complete oxidation of the TTF-type molecules, which form charged dimers associated with I{sub 3} ions, without any noticeable structural modification. A thermally activated process leads to a structural modification, where regular chains of triiodide are associated with an array of mixed valance EDTTTF(SC{sub 18}){sub 2} stacks. Besides using a vibronic model which considers both electron-molecular vibrations and electronic correlations in these systems, the authors have been able to interpret quantitively the optical absorption spectra. The authors have shown that they have a mixed-valance system with its own molecular organization, which can be used as a component in a chemical sensor or perhaps for nonlinear optical devices. 30 refs., 11 figs., 3 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 263811
- Journal Information:
- Journal of Physical Chemistry, Vol. 96, Issue 7; Other Information: PBD: 2 Apr 1992
- Country of Publication:
- United States
- Language:
- English
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