Vibrational spectroscopy of molecular constituents of one-dimensional organic conductors. Tetrathiofulvalene (TTF), TTF+, and (TTF+)2 dimer

Abstract

An extensive vibrational assignment of TTF and TTF‐d₄ is achieved, improving the previously reported one through the use of polarized infrared spectra of single crystals of the monoclinic form. Infrared spectra of the monoclinic and triclinic forms are compared and the different crystal field effects discussed. Powder Raman and infrared spectra of (TTF)Br_1.0 and (TTF‐d₄)Br_1.0, Raman depolarization ratios and infrared spectra of (TTF)ClO₄ and (TTF‐d₄)ClO₄ solutions are reported. The assignment of the a_g, b_1u, b_2u, and b_3u fundamental modes of (TTF)⁺ and (TTF‐d₄)⁺ radicals allows the identification of most of the relevant frequency shifts following the ionization of the TTF structure. The possible use of the ionization shifts for the study of the electronic charge distribution in the conducting TTF systems is considered. The parallel investigation of the concentration effects on the visible and infrared absorption spectra of TTF⁺ in solution let us to identify anomalous infrared absorptions associated with the formation of (TTF⁺)₂ dimer. They are attributable to an intensity borrowing from the charge transfer band due to the electron–molecular vibration (e–mv) interaction and their identification opens the way to an experimental evaluation of the e–mv coupling constants of TTF.