A Rigid Neutral Molecule Involving TTF and TCNQ Moieties with Intrinsic Charge- and Electron-Transfer Properties that Depend on the Polarity of the Solvent
โ Scribed by Evgeny Tsiperman; James Y. Becker; Vladimir Khodorkovsky; Alex Shames; Lev Shapiro
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 385 KB
- Volume
- 117
- Category
- Article
- ISSN
- 0044-8249
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โฆ Synopsis
Since the discovery [1] of the first organic metal in 1973, much attention has been devoted to the investigation of TTF, its derivatives, and analogues as electron-donor components for many charge-transfer (CT) complexes and ion-radical salts. [2] A proposed model of a unimolecular rectifier [3] involving TTF and TCNQ moieties linked covalently through a rigid saturated spacer has stimulated intensive studies in this direction. A concept involving a number of donor and acceptor units incorporated in a single molecule was later developed [4] that would enable the properties related to molecular organic conductors to be controlled. So far, the realization of this notion has been limited to linking moderate acceptors to TTF derivatives and weak donors to TCNQ fragments, [5] while the incorporation of TTF and TCNQ moieties in a single molecule has proved to be an elusive goal. [6] In 2003, Bryce and co-workers published [7] a synthesis of a TTF-s-TCNQ molecule containing a nonconjugated flexible spacer. This compound is expected to exhibit a high degree of intramolecular CT in both solution and the solid state. However, while its IR data are consistent with a degree of charge transfer of about 0.85 in the solid state, only less than 1 % biradicals were observed by EPR and UV/Vis/NIR spectroscopy. Also, the redox potentials shifted by only 20 mV with respect to those of the individual donor and acceptor components, thus indicating only a small degree of donor-acceptor interaction. Furthermore the authors claim of a thermally induced electron transfer in their system, which was based on temperature-dependent EPR measurements, is somewhat misleading. Their calculated HOMO/LUMO gap (0.17-0.75 eV) and measured energy of the CT transition (0.75 eV, red edge 0.45 eV) are much higher than the energy
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