Tetrathiafulvalenes oxidation potentials

Tricyclic dithiine derivatives of tetrathiafulvalene (TTF) 32 have been prepared for their increased electropolymerization potential <2000CC1005>. The effect of different tricyclic heterocycles upon the redox properties of TTF analogues was explored, and showed that the furan derivative 33 had an unusual nonplanar conformation that allowed for the attainment of higher oxidation states at relatively low oxidation potentials <2004JMC2822>. 

The incorporation of tetrathiafulvalene (TTF) into dendrimers presents a fascinating prospect for the following reasons (1) oxidation of TTF to the cation radical and dication species occurs sequentially and reversibly at very accessible potentials (for unsubstituted TTF, = +0.34 and eY = +0.78 V, vs. Ag/AgCl) (2) the oxidation potentials can be finely tuned by the attachment of appropriate substi-... 

There is a long standing interest in the chemistry and the properties of cyclic compounds containing sulfur atom in modern material chemistry due to their redox chemistry. In particular, the focus has been on dithiole derivatives, e.g., dithiafulvenes and tetrathiafulvalenes, since the finding of metallic conductivity and low temperature superconductivity in radical cation salts. The quite low oxidation potentials of 1,4-dithiin compounds have been reported, recently [109]. On the other hand, thioketene dimers (2,4-bis(alkyli-dene)-l,3-dithietane) have been known for more than 100 years and synthesized by various methods [110-115]. The structure of these dimer compounds is similar to that of the redox-active sulfur compounds therefore, the potential electronic property of the thioketene dimer moiety is considerably attractive with the aim of application to a new and better -donor. 

Many easily oxidized organic sulfides exist, but, of these, tetrathiafulvalene [2] (TTF) has been more extensively researched than most, because of interest in the electrical properties of its salts. Its oxidation potential makes it a reasonable electron donor [3]. Arenediazonium salts were chosen as the partner reagents since their electron-accepting properties had been well explored [4, 5]. Furthermore, reaction of TTF with diazonium salts had recently been discussed in the Russian literature [6], but this reported only the formation of the radical-cation, TTF+. We were keen... 

The mesogenic nickel dithiolenes were found to have reduction potentials (against calomel) of +0.06V and 0.76 V and as such were expected to form charge-transfer complexes with the mesomorphic, substituted tetrathiafulvalene (TTF) derivatives (Figure 89), which had oxidation potentials (also against calomel) of +0.43 V and +0.88 V. 

Tetraheterafulvalenes, such as bis(ediylenediseleno)tetrathiafulvalene, bis (me-thylenediseleno) tetrathiafulvalene, tetratellurafulvalenes, which are rich in selenium or tellurium hetero-atoms, showed two oxidation potentials, with values close to those of BEDTTTF, and a few of them gave highly conducting complexes (see [14],[25],[32] and refs therein). However, the low solubility in common organic solvents of these it-donors seriously hampers crystal-growing efforts, and often results in poor crystal quality [14] [32]. 

Electron mediators successfully used with oxidases include 2,6-dichlorophenolindophol, hexacyanoferrate-(III), tetrathiafulvalene, tetracyano-p-quinodimethane, various quinones and ferrocene derivatices. From Marcus theory it is evident that for long-range electron transfer the reorganization energies of the redox compound have to be low. Additionally, the redox potential of the mediator should be about 0 to 100 mV vs. standard calomel electrode (SCE) for a flavoprotein (formal potential of glucose oxidase is about -450 mV vs SCE) in order to attain rapid vectrial electron transfer from the active site of the enzyme to the oxidized form of the redox species. 

The electronic properties of n-conjugated polymers reflect well the basic electron-withdrawing or electron-donating properties of the components of the Ti-conjugated polymer [62]. In view of the electrochemical reduction potential, the thiophene unit and tetrathiafulvalene unit (Nos. 8 and 9 in Table 1) have a similar electronic effect in PAEs. It is reported that poly(arylenevinylene)s are also susceptible to electrochemical reduction [63, 64]. Due to the electron-accepting properties, PAEs are usually inert in electrochemical and chemical (e.g.,by I2 [54]) oxidation. 

As already pointed out in the case of rotaxanes, mechanical movements can also be induced in catenanes by chemical, electrochemical, and photochemical stimulation. Catenanes 164+ and 174+ (Fig. 19) are examples of systems in which the conformational motion can be controlled electrochemically [82, 83], They are made of a symmetric electron acceptor, tetracationic cyclophane, and a desymmetrized ring comprising two different electron donor units, namely a tetrathiafulvalene (TTF) and a dimethoxybenzene (DOB) (I64 1) or a dimethoxynaphthalene (DON) (174+) unit. Because the TTF moiety is a better electron donor than the dioxyarene units, as witnessed by the potentials values for their oxidation, the thermodynamically stable conformation of these catenanes is that in which the symmetric cyclophane encircles the TTF unit of the desymmetrized macrocycle (Fig. 19a, state 0). 

A slightly different behaviour is observed for the complex with the 3-(4,5-bis(methyl-thio)tetrathiafulvalen-4-ylthio)-2,4-pentanedionato anion (125), Mn(125)2 . It undergoes two oxidation processes (E° = 4-0.50 V and 4-0.79 V, vs. SCE, in 4 1 CH2Cl2 C2H50H) which are shifted towards less negative potential values by about 30 mV relative to those of the protonated 125, thus indicating that the functional group attached to acac... 

Charge-transfer processes occurring across the liquid-liquid interface have also been studied by EPR. The Galvani potential difference between the two immiscible solvents, water and 1,2-dichloroethane (DCE), was controlled electrochemically by means of a bipotentiostat. The water phase contained potassium ferrocyanide, which, in the DCE phase, by electrochemical polarization of the interface, can reduce a compound such as tetracyanoquinodimethane to its radical anion or oxidize a compound such as tetrathiafulvalene to its cation radical. Both radicals were detected by EPR spectroscopy [79]. 

During stepwise oxidation, each of the tetrathiafulvalene (TTF) or 4,5-dimethyltetrathiofulvalene (o-DMTTF) moieties in 90-92 donates two electrons so that exhaustive oxidation at potentials below IV (vs. SCE) leads to dications 90 + the tetracations 91" + and hexacations 92 +. In the initially formed radical cations... 

Table 5 Half-Wave Potentials for the Oxidation of Some Tetrathiafulvalenes and Related Compounds to the Corresponding Cation Radicals and Dications ... 

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