Examination of the Charge-Sensitive Vibrational Modes in Bis(ethylenedithio)tetrathiafulvalene

Abstract

We reinvestigated the two C=C stretching modes of the five-membered rings of ET (ET = bis(ethylenedithio)tetrathiafulvalene), namely, nu(2) (in-phase mode) and nu(27) (out-of-phase mode). The frequency of the nu(27) mode of ET(+) was corrected to be approximately 1400 cm(-1), which was identified from the polarized infrared reflectance spectra of (ET)(ClO(4)), (ET)(AuBr(2)Cl(2)), and the deuterium- or (13)C-substituted compounds of (ET)(AuBr(2)Cl(2)). It was clarified from DFT calculations that the frequency of the nu(27) mode of the flat ET(0) molecule was significantly different from that of the boat-shaped ET(0) molecule. We obtained the linear relationship between the frequency and the charge on the molecule, rho, for the flat ET molecule, which was shown to be nu(27)(rho) = 1398 + 140(1 - rho) cm(-1). The frequency shift due to oxidation is remarkably larger than that reported in previous studies. The fractional charges of several ET salts in a charge-ordered state can be successfully estimated by applying this relationship. Therefore, the nu(27) mode is an efficient probe to detect rho in the charge-transfer salts of ET. Similarly, a linear relationship for the nu(2) mode was obtained as nu(2)(rho) = 1447 + 120(1 - rho). This relationship was successfully applied to the charge-poor molecule of theta-type ET salts in the charge-ordered state but could not be applied to the charge-rich molecule. This discrepancy was semiquantitatively explained by the hybridization between the nu(2) and nu(3) modes.

Magnetic ordering and charge dynamics in κ-(BEDT-TTF)2Cu[N(CN)2]Cl

“…Measurements were made by an IR microscope on the thin sides of the crystals in the temperature range down to 12 K with 1 cm −1 resolution. Due to the strong and linear dependence of the ν 27 (b 1u ) eigenfrequency on the ionicity of the BEDT-TTF molecule of −140 cm −1 per electron [24,25], we are able to resolve variations in charge of less than 1%.…”

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

“…The linear relationship for the infrared-active ν 27 was first utilized by Moldenhauer et al, for estimating the iconicity of BEDT-TTF [12]. However, this relationship is given based on the incorrect assignment of BEDT-TTF + [46]. Subsequently, the relationship was not examined for long time, because this mode is usually hidden in a huge electronic absorption band when it is measured on the conducting plane or powdered samples.…”

“…Subsequently, the relationship was not examined for long time, because this mode is usually hidden in a huge electronic absorption band when it is measured on the conducting plane or powdered samples. Recently, Yamamoto et al, have examined the assignment of Kozlov et al, and they reassigned ν 2 , ν 3 , and ν 27 of BEDT-TTF + with the aid of 13 C and deuterium substituted compounds [46]. First they examined ν 27 employing the polarization perpendicular to the conducting layer on the side face of single crystals.…”

THz-Frequency Modulation of the HubbardUin an Organic Mott Insulator

“…The excitation of local modes at mid-infrared frequencies is different from the case of nonlinear phononics in that the molecular orbital and concomitantly the onsite charge density are controlled [12,13], with each site maintained in its electronic ground state.…”