The low energy phonon modes of the hydrogenated and deuterated π-conjugated system 7,7,8,8-tetracyanoquinodimethane: an inelastic neutron scattering study.

Abstract

The organic acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), has been the subject of much research over the past few decades. Due to the π-conjugation of the quinodal structure, TCNQ as well as TCNQ based charge transfer compounds, exhibit some remarkable conducting properties. We present a study of the neutral TCNQ using inelastic neutron spectroscopy (INS) and show the first temperature dependent INS data collected on TCNQ allowing us to probe the temperature dependence of the low energy vibrational states, which have been shown to have an effect on charge delocalisation. Computational calculations have been used to help understand the data and the combination with the INS allows us to understand the phonon states. A complimentary experiment on deuterated TCNQ was also performed that allows a brief comparison of the isotopic substitution. This work utilises novel techniques to aid the understanding of the bulk properties of TCNQ in its neutral state that can be fed into work on other TCNQ based materials, including the exploration of deuteration as a technique to tune the properties of the parent compound.