Spectroscopic studies of charge localization in organic metals (DMtTTF)2X (X = ClO4, ReO4)

Abstract

AbstractWe report on IR and Raman investigations of two isostructural quasi‐one‐dimensional charge‐transfer salts (DMtTTF)2X (X= ClO4, ReO4) with strictly regular conducting stacks. At room temperature the salts show metallic properties and below Tρ = 100‐150 K they undergo a transition to the semiconducting state. Polarized infrared reflectance (700‐16000 cm‐1) and Raman spectra (50‐3500 cm‐1) of single crystals were measured in the temperature range T = 5‐300 K. Additionally, vibrational spectra of neutral DMtTTF were also measured. Closer inspection of each salt's Raman spectra reveals that the charge distribution among the partially oxidized DMtTTF donors within the quasi‐one‐dimensional stacks remains uniform throughout the whole temperature range. The IR electronic plasma‐edge‐like dispersion can be well fitted with a Lorentz dielectric function, typical for semiconducting materials. Infrared vibrational features related to C=C stretching indicate significant electron‐molecular vibration coupling. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)