Premium
Infrared and Raman spectroscopic studies of the charge localization in one‐dimensional organic metals (DMtTTF) 2 X (X = ReO 4 , ClO 4 ) with regular organic stacks
Author(s) -
Jankowski Damian,
Świetlik Roman,
Jeannin Olivier,
Assaf Ali,
Reinheimer Eric W.,
Fourmigué Marc
Publication year - 2013
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.4405
Subject(s) - raman spectroscopy , tetrathiafulvalene , chemistry , isostructural , valence (chemistry) , molecule , infrared , infrared spectroscopy , density functional theory , spectral line , molecular vibration , analytical chemistry (journal) , crystallography , computational chemistry , crystal structure , physics , organic chemistry , chromatography , astronomy , optics
A novel selective synthesis of the unsymmetrically substituted tetrathiafulvalene dimethyltrimethylene‐tetrathiafulvalene (DMtTTF) is described together with its electrocrystallization to the known conducting mixed‐valence ClO 4 – and ReO 4 – salts. Infrared (IR) and Raman spectra of the two isostructural quasi‐one‐dimensional cation radical salts (DMtTTF) 2 X (X = ReO 4 – , ClO 4 – ) are investigated as a function of temperature ( T = 5–300 K). At ambient temperature, these salts show metallic‐like properties and below T ρ = 100–150 K, they undergo a smeared transition to semiconducting state. To study this charge localization, we measured temperature dependence of polarized IR reflectance spectra (700–16 000 cm –1 ) and Raman spectra (150–3500 cm –1 , excitation λ = 632.8 nm) of single crystals. For both compounds, the Raman data and especially the bands related to the C=C stretching vibration of the DMtTTF molecule show that the charge distribution on molecules is uniform down to the lowest temperatures. Similarly, IR data confirm that down to the lowest temperatures, there is neither charge ordering nor important modification of the electronic structure. However, the temperature dependence of Raman spectra of both salts reveals a regime change at about 150 K. Additionally, using Density Functional Theory (DFT) methods, the normal vibrational modes of the neutral DMtTTF 0 and cationic DMtTTF + species and also their theoretical IR and Raman spectra were calculated. The theoretical data were compared with the experimental IR and Raman spectra of neutral DMtTTF 0 molecule. Copyright © 2013 John Wiley & Sons, Ltd.