Tetrathiofulvalenes

Carrier generators in molecular conductors have been associated for a long time to a partial charge transfer between the HOMO (or LUMO) electronic band and other chemical species. These systems are known as two-component molecular conductors. Tetrathiofulvalene derivatives are versatile systems for the formation of molecular organic conductors due to their electron donor capacity by transferring one u-electron from the HOMO orbital, and to their planar shape that promotes their stacking as a consequence of the n-n orbital overlap. The electronic properties of these salts are essentially determined by the packing pattern of the donor molecules which, in turn, depends on the counter-ion. 

Espinosa, E., Molins, E. and Lecomte, C. (1997), Electron density study of the one dimensional organic metal bis(thiodimethylene)-tetrathiofulvalene tetracyanoquinodimethane, Phys. Rev. B, 56(4), 1820-1833. 

Authors [143] suppose that sulfur atoms are not affected by oxidation and only act as activating double bond substituents. However, the analysis of the electronic structure of tetrathiofulvalene shows that, resulting from the interaction of tt CC) and 7t(S) orbitals, HOMO of this molecule is an antibonding combination of jr and riji orbitals with the predominant contribution being from the latter. Indeed, the substitution of one or more S atoms with Se results in a less conjugated system and, as a consequence, in higher oxidation potentials [144]. 

Other conditions being equal, the first oxidation potentials of tetrathiofulvalenes are usually less positive than those of tetrathioethylenes [141-151]. The first reversible oxidation of tetrathiofulvalenes normally occurs at 0.2-0.8 V versus SCE, whereas the second occurs at 0.6-1.2V... 

PSTTF is based on polystyrene that has been functionalized through appendage of a tetrathiofulvalene side-chain. The resist is spin-coated from a solution which contains a sensitizer substance, typically a perhaloalkane... 

Figure 39. Polystyrene-tetrathiofulvalene resist. The sensitizer is a perhaloaliphatic such as CBr. Exposure results in salt formation in the exposed areas of the resist film.

Redox-active tetrathiofulvalenes undergo a [2-f2] cycloaddition in the solid state to provide the corresponding dimeric photoadduct (Equation 47) <2004CC1538>. 

In addition to ferrocene, the oxidative redox couple that has received the most attention in supramolecular chemistry is tetrathiofulvalene (TTF), 35. This compound undergoes two reversible one-electron oxidations, first to a radical cation and then to a dication (Eq. 1.21). TTF first came to prominence in the 1970s when it was discovered that the charge transfer complex between it and 7,7,8,8-tetracyanoquinonedimethane (TCNQ) shows metallic conductivity. As a result, a large variety of different TTF derivatives have been prepared and characterized. This rich synthetic chemistry, coupled with the electroactivity, has intrigued supramolecular chemists for some time, with the result that the TTF unit has been incorporated into a wide variety of... 

It was indicated earlier that swelling limits resolution in solvent-developed negative resists. It was also intimated that swelling effects could be minimized if there were a sufficient polarity change between the exposed and non-exposed areas of the type mentioned in the previous discussion of the PBOCST system. A similar principle was utilized by Hofer et al., (145-146) at IBM, based on ion pair formation. The resist consists of a polystyrene polymer to which tetrathiofulvalene (TTF) units have been attached. When spun down with an acceptor such as CBr4, a complex is formed which, on irradiation, undergoes an electron transfer reaction to form an ion pair ... 

Earlier, I criticized the Cooper pair being philosophically unacceptable because the proposed pair is not seen elsewhere outside of the BCS superconductivity theory. The same measurement must be placed against the Covalon-Conduction theory proposed here. We shall show therefore, that a number of physical property changes observed in [TCNQ-TTF] (tetracyano-p-quinodimethane-tetrathiofulvalene), an organic compound, as a function of temperature can be interpreted and understood in terms of Covalon-conduction . 

A few other types of anion sensors have been mentioned recently in the literature. Tetrathiofulvalene microcrystals immobilised at a platinum electrode displayed electrochemical properties that were affected by the presence of anions in solution, with some selectivity for anions such as bromide [ 145]. A flow-injection analysis system using anion-exchange columns for separation and polyaniline electrodes as detectors could detect dichromate down to 0.004 ppb and could be used for seawater samples [146]. 

The 19F NMR spectrum of the cycloadduct from the reaction between 2//-thiopyran-2-thionc, derived from tetrathiofulvalene by loss of CS2, and the fluorinated fullerene C60F18 shows only 16 fluorine atoms indicating that the [2+2]-cycloaddition involved the loss of two F atoms. The most upfield signal is associated with the F atoms adjacent to the donor sulfur addend <2003GEJ2008>. 

There is a very short list of organic semiconductors with reported thin-film field-effect mobilities greater than 1 cm2 V-1 s h These include pentacene, sexithio-phene [5a], and anthradithiophene [17]. If we extend this list to include single crystal and n-type materials, we can add perylene [18], rubrene [19], copper phtha-locyanine (CuPc) [20], tetracyanoquinodimethane (TCNQ) [21], and dithiophene-tetrathiofulvalene (DT-TTF) [22] - still a short list. 

A second breakthrough followed with the synthesis of tetrathiofulvalene (TIT) by Wudl and co-workers [17] in 1970 and the discovery by Coleman et al. [18] in 1973 of metallic conductivity in TTF-TCNQ down to about... 

Thiapendione (12) also serves as a convenient starting material for the preparation of symmetrically substituted tetrathiofulvalenes [6]. It is formed by refluxing a,a-dichloroacetate esters with potassium O-isopropyl dithio-carbonate, followed by an acid-catalyzed cyclization [27]. One carbonyl group of thiapendione can be selectively cleaved in benzene-water in the... 

Reaction of Tetrahaloethylenes with 1,2-Dithiolates 1,2-Dithiolate anions react with tetrahaloethylenes to furnish substituted tetrathiofulvalenes. This method has proven particularly useful in preparing dibenzotetrathiafulvalene (17) and its derivatives [41-43]. 

Infinite Stacks of TCNQ and TTF Molecules.—The quasi one-dimensional charge-transfer molecular crystal TCNQ (7,7, 8,8 -tetracyanoquinodimethane)-TTF (tetrathiofulvalene) has received considerable attention in the past decade because of its interesting solid-state physical properties. In recent publications81... 

This synthesis provides easy and inexpensive access to the 4,5-dithio-l, 3-dithiole-2-thione system. By alkylation with 1,2-dibromoethane, 4,5-ethyienedithio-1,3-dithiole-2-thione, a key intermediate in the synthesis of bis(ethylenedithio)tetrathiofulvalene (BEDT-TTF) is obtained.4 5 BEDT-TTF forms... 

A limited number of organic substances with two lattices is also known all columnar misfit structures. The crystal structure of hepta(tetrathiofulvalene)-pentaiodide, (TTF)7l5, determined by Johnson and Watson is one of the best described. [The substructures of the two components (TTF and iodine) were also determined - but in projection only - by Daly and Sanz ] In it, columns of TTF molecules form a matrix, the channels within which are filled by rows of iodine atoms. The 7 5 ratio of subcell multiplicities is only approximate within about 1% of the true ceD value. Similar structures have been determined for (TTF)Br , with a variable ratio of component subcells... 

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