From switched molecular self-assembly in solution to radical conductors in solid state

  • Authors

    Manuel Souto,1 HengBo Cui,2 Miriam Peña-Álvarez,3 Valentín G. Baonza,3 Harald O. Jeschke,4 Milan Tomic,4 Roser Valentí,4 Davide Blasi,1 Imma Ratera,1 Concepció Rovira,1 and Jaume Veciana1

  • Publication

    Pressure-Induced Conductivity in a Neutral Nonplanar Spin-Localized Radical
    Journal of the American Chemical Society, 138, 11517−11525, 2016
  • Figure

    Dyads formed by tetrathiafulvalene (TTF) linked to polychlorotriphenylmethyl (PTM) radicals exhibit interesting physical properties such as bistability in solution or conductivity in solid state.

During the last decades, numerous efforts have been made to design new multifunctional materials which involve the interplay between multiple physical properties (i.e. electrical, optical, and magnetic properties). Multifunctional molecular materials can be even more interesting if they are able to switch between two or more states modifying their physical properties upon the application of external stimuli (i.e. temperature, pressure, light or an electric field). One of these materials are the organic donor–acceptor (D–A) systems formed by the electron-donor tetrathiafulvalene (TTF) linked to the electron-acceptor perchlorotriphenylmethyl (PTM) radical through different π-conjugated bridges exhibiting interesting physical properties such as bistability in solution or conductivity in solid state. Understanding the interplay between intra- and intermolecular charge transfer processes in solution is of high interest in order to rationalize the self-assembling ability and conducting properties of such dyads in solid state.

In 2012 we reported a D–A dyad that consists of the electron-acceptor PTM radical linked to a TTF through a vinylene bridge. This organic radical dyad exhibited a reversible switching from its neutral to its zwitterionic state that can occur through an intramolecular electron transfer (IET) process from the TTF to the PTM radical simply by modification of the solvent polarity. In addition, it was demonstrated that the IET process promoted self-assembly of the dyads in the zwitterionic states to form diamagnetic dimers in DMF at room temperature. Moreover, this dyad exhibits a reversible temperature-induced switching in DMF solution between diamagnetic dimers, observed at room temperature, and paramagnetic monomers at high temperature. More recently, we have also studied the switching of optical and magnetic properties in solution of an A–D–A diradical triad based on two PTM radicals connected through a TTF-vinylene bridge through an electrochemical input.

Regarding the properties in solid state, we synthesized other similar a TTF-based radical dyads in order to improve the self-assembly of the TTF moieties. In view of the supramolecular architecture of this radical dyad with segregated donor and acceptor units, we aimed to promote conductivity upon the application of high pressure. Indeed, we have recently reported the resistivity measurements of this radical dyad at high pressure, indicating semiconductor behaviour thanks to increased electronic bandwidth and charge reorganization as ascertained by theoretical calculations. Overall we believe that the results described here are a proof of concept of a novel strategy providing an important insight into the design of new radical based conductors.

Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)/CIBER-BBN, Spain
Condensed Molecular Materials Laboratory, RIKEN, Japan
3 Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Spain
4 Goethe-Universität Frankfurt, Germany

Institut de Ciència de Materials de Barcelona
Campus de la UAB 08193 Bellaterra, SPAIN

Tel: +(34) 935 801 853
Fax: +(34) 935 805 729
Alejandro Santos 
Anna May-Masnou
Graphic Design
José Antonio Gómez

José Antonio Gómez 
Albert Moreno