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)Br1.0 and (TTF-d4)Br1.0, Raman depolarization ratios and infrared spectra of (TTF)ClO4 and (TTF-d4)ClO4 solutions are reported. The assignment of the ag, b1u, b2u, and b3u 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.

Infrared Investigations of the Neutral-Ionic Phase Transition in TTF-CA and Its Dynamics

“…Yet, the structure of TTF is planar in the condensed phase and allows us to imply D 2h . The labeling of the modes in Table 2 is according to Girlando et al [49] and Bozio et al [47]. The calculations reveal an inner distance of the C=C double bonds in TTF 0 of 1.346 Å, which agrees very well with the experimentally determined value of d = 1.35 Å in the gaseous phase [46].…”

“…The intensity also increases slightly, as predicted by the theoretical calculations (see Table C2 in Appendix C). At room temperature, further weak maxima can be recognized at higher frequencies, which we ascribe to the ν 25 (b 2u )-mode of TTF [47]. According to Table C2, theory predicts the mode to appear at ν = 802 cm −1 , but it is shifted due to the ionicity, in this case to 805 cm −1 .…”

“…The results agree well with previous calculations [15,45,46], albeit less precise DFT-methods as basis sets were employed. For both molecules, the vibrational modes can be classified according to the D 2h [47] symmetry as follows:…”

Potential model for tetrathiafulvalene based on inelastic neutron scattering and Raman spectra

“…The assignments used were the solution values of Bozio et al 11 and with the exception of the assignment of 530 cm Ϫ1 as a B 2g mode these were also the assignments used by Liu et al 12 We favor an assignment of the B 2g mode at 250 cm Ϫ1 based on the bands observed in this region in both the INS and Raman spectra.…”

“…Eldridge et al 9 have studied the room temperature infrared and Raman spectra of BEDT-TTF and four of its isotopic analogs and report a modified valence force model that successfully predicts most of the in-plane and a few of the ethylene out-of-plane modes. The work of Bozio et al 10,11 remains the definitive infrared and Raman study of TTF and TTF 1.0 and their force fields satisfactorily explain most of the in-plane modes. More recently, Liu et al 12 have used a combination of density functional theory and ab initio MP2 calculations to study the structures and vibrational spectra of both BEDT-TTF and TTF.…”