Electron-molecular vibration coupling in (DMtTTF)Br and (o-DMTTF)2[W6O19] salts studied by vibrational spectroscopy

• We report a spectral study of two recently synthesized charge-transfer salts.
• Electronic and vibrational properties are discussed.
• Electron-molecular vibration-coupling phenomena are analyzed.
• Coupling constants for the unsymmetrical donors are experimentally determined.
• Stretching vibrations of CC bonds exhibit the strongest coupling with electrons.

A novel 1:1 salt encompassing radical cations of DMtTTF (DMtTTF = dimethyltrimethylene–tetrathiafulvalene) and the Br−anion has been synthesized. Close inspection of the salt's solid state structure revealed the presence of quasi-isolated dimers containing DMtTTF radical cations, a specific arrangement whereby the microscopic parameters of DMtTTF+ might be studied. Analysis of the corresponding single crystal IR and Raman spectra of (DMtTTF)Br allowed us to study the material's electronic and vibrational structure and to evaluate the electron-molecular coupling constants via the isolated dimer model. Additionally, using previously published IR data, analogous calculations were performed on the salt (o-DMTTF)2[W6O19] (o-DMTTF = o-3,4-dimethyltetrathiafulvalene), which also contains well isolated dimers of o-DMTTF radical cations. These calculations revealed that the coupling constants for the unsymmetrical donors studied herein are comparable to those for symmetric TTF derivatives.