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

• Published in: Physical chemistry chemical physics : PCCP Vol. 23; no. 4; pp. 2899 - 295
• Main Authors: Berlie, Adam, Cavaye, Hamish
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 04.02.2021
• Subjects: Charge transfer; Conjugation; Deuteration; Inelastic scattering; Neutron scattering; Neutrons; Phonons; Properties (attributes); Temperature dependence; Tetracyanoquinodimethane; Vibrational states
• ISSN: 1463-9076; 1463-9084; 1463-9084
• DOI: 10.1039/d0cp06253g

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. TCNQ is a fascinating molecule with potential for optical, electronic and magnetic materials. Our work studies the low energy lattice modes of the parent compound to further understand the vibrational properties including their temperature dependence.