Hydrogen bond-promoted metallic state in a purely organic single-component conductor under pressure

Abstract

Purely organic materials are generally insulating. Some charge-carrier generation, however, can provide them with electrical conductivity. In multi-component organic systems, carrier generation by intermolecular charge transfer has given many molecular metals. By contrast, in purely organic single-component systems, metallic states have rarely been realized although some neutral-radical semiconductors have been reported. Here we uncover a new type of purely organic single-component molecular conductor by utilizing strong hydrogenbonding interactions between tetrathiafulvalene-based electron-donor molecules. These conductors are composed of highly symmetric molecular units constructed by the strong intra-unit hydrogen bond. Moreover, we demonstrate that, in this system, charge carriers are produced by the partial oxidation of the donor molecules and delocalized through the formation of the symmetric intra-unit hydrogen bonds. As a result, our conductors show the highest room-temperature electrical conductivity and the metallic state under the lowest physical pressure among the purely organic single-component systems, to our knowledge.

Two Closely Related Organic Charge-Transfer Complexes Based on Tetrathiafulvalene and 9H-fluorenone Derivatives. Competition between Hydrogen Bonding and Stacking Interactions

“…Regarding hydrogen bonding, it is well documented that, under favorable circumstances, such bonds are able to cooperate with CT interactions, to modulate the transport properties in the material [29]. The deliberate choice of engaging A and D precursors functionalized by strong hydrogen bond donor/acceptor groups remains a viable strategy in the field of organic conductors [30], and has indeed produced outstanding results [31,32]. Finally, even for complexes close to the neutral state, the spectroscopic determination of δ seems to afford reliable data.…”

Development of Novel Functional Organic Crystals by Utilizing Proton- and π-Electron-Donating/Accepting Abilities

“…The previous section demonstrates that S/Se substitution in the TTF skeleton of the present organic conductors significantly enhances the intermolecular π-electron interactions and electrical conductivity. 8,10 The resulting very small activation energy (0.02 eV) in D-ST suggests that metallic behavior appears if the intermolecular π-electron interactions are increased a little more. Therefore, the tetraselenafulvalene (TSF) analogue, where all four sulfur atoms in the TTF skeleton are replaced by selenium, was designed (Chart 1).…”

“…This section introduces a purely organic conductor, κ-H 3 (Cat-EDT-TTF) 2 (Chart 1; abbreviated as H-TTF, Cat-EDT-TTF = catechol-fused ethylenedithiotetrathiafulvalene), 10 which underlies the present work. As is the case with (BEDT-TTF) 2 X (Figure 1), organic conductors are usually CT salts or complexes, composed of an electron-donor molecule and a counter anion or an electron-acceptor molecule.…”

Synthesis and Characterization of Ethylenedithio-MPTTF-PTM Radical Dyad as a Potential Neutral Radical Conductor

“…In this sense, most of these systems are based on delocalized and planar radicals in order to increase the W/U ratio, such as spirobisphenalenyl [4][5][6] and thiazolyl radicals [7][8][9] reported by Haddon and Oakley, respectively. In addition, Mori and coworkers have also recently reported a purely-organic single-component conductor by utilizing strong hydrogen-bonding interactions between tetrathiafulvalene (TTF)-based electron-donor molecules [10,11].…”