Charge-sensitive vibrational modes in the (EDT-TTF-OX)_2AsF_6 chiral molecular conductors

TL;DR

This study investigates charge-sensitive vibrational modes in chiral molecular conductors (EDT-TTF-OX)_2AsF_6 using infrared and Raman spectroscopy, supported by DFT calculations, revealing a consistent charge density and ruling out charge ordering as the M-I transition cause.

Contribution

It combines experimental vibrational spectra with theoretical DFT calculations to analyze charge distribution in chiral molecular conductors, providing new insights into their electronic properties.

Findings

Charge density on EDT-TTF-OX is approximately +0.5 across all samples.

Charge-sensitive vibrational modes are identified and analyzed.

The M-I transition is not due to charge ordering.

Abstract

Infrared and Raman spectra of the three chiral molecular conductors (EDT-TTF-OX)_2AsF_6, comprising two salts based on enantiopure EDT-TTF-OX donor molecules and one based on their racemic mixture, have been measured as a function of temperature. In the frequency range of the C=C stretching vibrations of EDT-TTF-OX, charge-sensitive modes are identified based on theoretical calculations for neutral and oxidized EDT-TTF-OX using density functional theory (DFT) methods. The positions of the C=C stretching modes in both Raman and infrared spectra of the (EDT-TTF-OX)_2AsF_6 materials are analyzed assuming linear relationship between the frequency and charge on the molecule. The charge density on the EDT-TTF-OX donor molecule is estimated to be +0.5 in all the investigated materials and does not change with temperature. Therefore it is suggested, that M-I transition observed in (EDT-TTF-X)_2AsF_6 chiral molecular conductors at low temperature is not related to the charge ordering mechanism.