Vibrational and Electronic-spectra of One-dimensional Organic Charge-transfer Crystals - Model For A Tetramerized Cluster Structure

Recently synthesized organic charge-transfer crystals have been shown to display an interesting stack structure of the type ...DAADDAAD... (D denotes the donor molecule, A denotes the acceptor molecule), in which a self-charge-transfer interaction AA or DD alternates with a DA one. A theoretical model is developed for a tetrameric cluster DAAD or ADDA which can account for the coexistence of both types of interaction. The model is based on an electronic extended Hubbard Hamiltonian and also takes into account the interaction between electrons and molecular vibrations. A description of the optical and Raman spectra of the model system is achieved and used to study some complicated features observed in the spectra of the charge-transfer complex TTF-TCNE (TTF denotes tetrathiafulvalene, TCNE denotes tetracyanoethylene).