Hydrogen-Bonding-Assisted Self-Doping in Tetrathiafulvalene (TTF) Conductor

Kobayashi, Yuka; Yoshioka, Masumi; Saigo, Kazuhiko; Hashizume, Daisuke; Ogura, Takashi

doi:10.1021/ja809425b

Cited by 75 publications

(46 citation statements)

References 65 publications

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“…Most studies of the molecular conductors based on hydrogen bond-functionalized TTF derivatives have focused on the tuning of the molecular self-assembly and the HOMO/LUMO energy levels 47,48 . In this context, several groups have recently reported that the introduction of the hydrogen bond has another important role, that is, the generation of the charge carriers 46,49 . Besides the carrier generation, our system demonstrates that the symmetric hydrogen bond constructs the new type of the purely organic single-component molecular conductors which are composed of highly symmetric molecular units.…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2013

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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.

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Section: Discussionmentioning

confidence: 99%

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

et al. 2013

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“…The adopted approaches were found to accurately describe the orbital configuration in several earlier studies of different SOMO-HOMO converted radicals [6][7][8] . We find that orbital arrangements obtained using single-reference methods are strongly dependent on the method, basis set, type of wave function and even software code 41 .…”

Section: Methodsmentioning

confidence: 99%

“…1b) 7 and carboxy-TTF crystals (3, Fig. 1c) 8 , the latter representing the first fully organic self-doped molecular conductor. Structure and proposed mechanism of "spin-polarization" 9 of the donor's HOMO in nitronyl nitroxidetetrathiafulvalene compounds 6 .…”

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confidence: 98%

“…b, Structure, energy diagram of the density functional theory (DFT) molecular orbitals and scheme of two-electron oxidation of SOMO-HOMO converted TEMPO (2,2',6,6'-tetramethylpiperidine-N-oxyl) bound dithiolate (2-thioxo-1,3-dithiole-4,5-dithiolate) complex of Ni 2+ , accompanied by intramolecular cyclization of an initially formed triplet biradical 7,10 . c, Schematic structure and energy diagram of the CASSCF molecular orbitals of a tetramer of the carboxy-TTF ammonium salt 8 .…”

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confidence: 99%

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Switching radical stability by pH-induced orbital conversion

et al. 2013

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In most radicals the singly occupied molecular orbital (SOMO) is the highest-energy occupied molecular orbital (HOMO); however, in a small number of reported compounds this is not the case. In the present work we expand significantly the scope of this phenomenon, known as SOMO-HOMO energy-level conversion, by showing that it occurs in virtually any distonic radical anion that contains a sufficiently stabilized radical (aminoxyl, peroxyl, aminyl) non-π-conjugated with a negative charge (carboxylate, phosphate, sulfate). Moreover, regular orbital order is restored on protonation of the anionic fragment, and hence the orbital configuration can be switched by pH. Most importantly, our theoretical and experimental results reveal a dramatically higher radical stability and proton acidity of such distonic radical anions. Changing radical stability by 3-4 orders of magnitude using pH-induced orbital conversion opens a variety of attractive industrial applications, including pH-switchable nitroxide-mediated polymerization, and it might be exploited in nature. AbstractIn most radicals the singly-occupied molecular orbital (SOMO) is the highest-energy occupied one

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“…43 Electron-rich TTF derivatives can undergo protonationinduced oxidative degradation in the presence of water. 44,45 Moreover, only the first redox reaction (pTTF → pTTF +• ) is accessible in aqueous electrolyte in the potential 'window' within which adsorbed thiols on gold are stable. We therefore sought a water-free electrochemical environment in which to study the single-molecule conductance of 6pTTF6 in the absence of water.…”

Section: ■ Experimental Methodsmentioning

confidence: 99%

Single-Molecule Electrochemical Gating in Ionic Liquids

et al. 2012

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The single-molecular conductance of a redox active molecular bridge has been studied in an electrochemical single-molecule transistor configuration in a room-temperature ionic liquid (RTIL). The redox active pyrrolo-tetrathiafulvalene (pTTF) moiety was attached to gold contacts at both ends through −(CH2)6S– groups, and gating of the redox state was achieved with the electrochemical potential. The water-free, room-temperature, ionic liquid environment enabled both the monocationic and the previously inaccessible dicationic redox states of the pTTF moiety to be studied in the in situ scanning tunneling microscopy (STM) molecular break junction configuration. As the electrode potential is swept to positive potentials through both redox transitions, an ideal switching behavior is observed in which the conductance increases and then decreases as the first redox wave is passed, and then increases and decreases again as the second redox process is passed. This is described as an “off–on–off–on–off” conductance switching behavior. This molecular conductance vs electrochemical potential relation could be modeled well as a sequential two-step charge transfer process with full or partial vibrational relaxation. Using this view, reorganization energies of ∼1.2 eV have been estimated for both the first and second redox transitions for the pTTF bridge in the 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIOTf) ionic liquid environment. By contrast, in aqueous environments, a much smaller reorganization energy of ∼0.4 eV has been obtained for the same molecular bridge. These differences are attributed to the large, outer-sphere reorganization energy for charge transfer across the molecular junction in the RTIL.

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Hydrogen-Bonding-Assisted Self-Doping in Tetrathiafulvalene (TTF) Conductor

Cited by 75 publications

References 65 publications

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

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

Switching radical stability by pH-induced orbital conversion

Single-Molecule Electrochemical Gating in Ionic Liquids

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