Electron-Molecular Vibration Coupling in TTF-Based Donors

Abstract

BEDT-TTF, BMDT-TTF and BEDO-TTF are well known thio-TTF and oxo-TTF (in the former case) derivatives on the basis of which cation--radical salts with 2D type of conductivity can be produced. In this work the comparative analysis of electron-molecular vibration coupling constants (obtained by MNDO quantum-chemical method) that describe the interaction between totally symmetric A g modes and electron on HOMO level is performed.

Experimental Evidence of the Symmetry Breakdown in 4,8-Diethoxy-2,7-bis(benzo-1‘,3‘-dithiol-2‘-ylidene)-1,3,5,7-tetrathia-s-indacene Compounds

“…This is a typical shape for the infrared absorption spectrum in this region for TTF-based low-dimensional organic conductors, which has been associated with the electron−molecular vibrations coupling (EMVC) effect. , The mechanism of this effect can be described as an electron oscillation between the adjacent molecules with overlapping partially occupied MO (dimers) induced by the molecular vibrations. In such compounds, the totally symmetrical CC and CS bonds stretching modes have the highest EMVC constants. , In the presence of EMVC these normally infrared-inactive A g modes become infrared-active for the light polarized in the direction of the dimer axis. Such an effect can be detected in the intense and broad so-called vibronic bands observed in the infrared spectrum of 1 x PF 6 , which are shifted to frequencies lower than those arising from the parent A g modes.…”

“…In such compounds, the totally symmetrical CdC and CsS bonds stretching modes have the highest EMVC constants. 22,23 In the presence of EMVC these normally infrared-inactive A g modes become infraredactive for the light polarized in the direction of the dimer axis. Such an effect can be detected in the intense and broad socalled vibronic bands observed in the infrared spectrum of 1 x -PF 6 , which are shifted to frequencies lower than those arising from the parent A g modes.…”

The temperature dependence of the infrared reflectance spectra of the organic superconductor and the organic metal

“…Infrared reflectance spectra of the compounds could assist considerably in the understanding of the compounds' electron band structures, and thus help in the solving of this problem. Despite the fact that the assignment of the BEDO-TTF molecule vibrational modes, and the calculation of their electron-molecular vibration coupling constants were performed some years ago, and form a good basis for these investigations [5,6], the single-crystal data have been limited up to now to studies of the room temperature reflectance of (BEDO-TTF) 2 ReO 4 •H 2 O [7,8]. The aim of this paper is to investigate in some detail the temperature dependences of the infrared reflectivity for both the superconducting salt (BEDO-TTF) 2 ReO 4 •H 2 O and the metallic (nonsuperconducting) salt (BEDO-TTF) 2 Cl•3H 2 O, in an attempt to understand the electronic structure of these compounds.…”