Voltammetry and Spectroelectrochemistry of TCNQ in Acetonitrile/RTIL Mixtures

Understanding the solvation and ion-pairing interactions of anionic substrates in room-temperature ionic liquids (RTIL) is key for the electrochemical applications of these new classes of solvents. In this work, cyclic voltammetry and visible and infrared spectroelectrochemistry of tetracyanoquinodimethane (TCNQ) was examined in molecular (acetonitrile) and RTIL solvents, as well as mixtures of these solvents. The overall results were consistent with the formation of RTIL/acetonitrile nanodomains. The voltammetry indicated that the first electrogenerated product, TCNQ^-, was not incorporated into the RTIL nanodomain, while the second electrogenerated product, TCNQ^2-, was strongly attracted to the RTIL nanodomain. The visible spectroelectrochemistry was also consistent with these observations. Infrared spectroelectrochemistry showed no discrete ion pairing between the cation and TCNQ^- in either the acetonitrile or RTIL solutions. Discrete ion pairing was, however, observed in the acetonitrile domain between the tetrabutylammonium ion and TCNQ^2-. On the other hand, no discrete ion pairing was observed in BMImPF₆ or BMImBF₄ solutions with TCNQ^2-. In BMImNTf₂, however, discrete ion pairs were formed with BMIm⁺ and TCNQ^2-. Density function theory (DFT) calculations showed that the cations paired above and below the aromatic ring. The results of this work support the understanding of the redox chemistry in RTIL solutions.