Tetrathiafulvalene units

The convergent synthesis of a range of aryl ester dendrimers with peripheral tetrathiafulvalene units was also reported (Devonport et al. 1998). The dendrimers acquire some amount of the cation-radical tetrathiafulvalene tips on reacting with iodine in solutions. Another promising material is polyphenylene dendrimers functionalized with benzophenone units. On being transformed into the potassium ketyl derivatives, the dendrimers bring forth intermolecular biradicals. These technically attractive species contain four-membered cycles that coordinatively combine two potassium cations... 

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. 

Photoinduced intramolecular electron transfer in the donor-acceptor complex 87 (R = H) generates transient charge-separated open-shell species with the remarkably long lifetime of about 75 ps [89]. Dyads that contain Tt-extended tetrathiafulvalene units also form stable cationic species upon oxidation [90]. The dumbbell shaped triad 91 [91-93] (Scheme 4.13) was obtained by carrying out the reaction with the in situ generated bis-diene at room temperature, in the dark and in o-dichlorobenzene as a solvent in 50% yield. The product is thermally unstable and easily undergoes a retro-Diels-Alder reaction [91]. 

As an example, the cyclic voltammograms (Fig. 7.2a) of 4 adsorbed on gold show the reversible oxidation of the tetrathiafulvalene unit to the corresponding radical... 

Novel triads that contained tetrathiafulvalenes as electron donors and porphyrin chromophores (refer to previous section for porphyrin-fullerene dyads) as donor units have been recently reported [246] (Scheme 12). Improved analogs of the latter triads were soon considered by connecting the tetrathiafulvalene unit to a 7r-extended conjugated network [247]. 

Scheme 4.33. Introduction of tetrathiafulvalene units into the lipophilic backbone of two-directional arborols for the construction of molecular wires .

The relative amounts of tri-and penta-iodide depend on the nature of the polymer, presumably because of varying ability of the structures to accommodate the two ions, and the possibility of weak interactions, e.g., with sulphur atoms of tetrathiafulvalene units. This is strikingly shown by the conversion of I - and I3 into I5 when polyvinyl alcohol film is stretched. 

The host 1 4PF6 and the guest 13 form [ref 16] (step 1 in Fig. 10.8) spontaneously the [2]pseudorotaxane [1 13] 4PF6 when mixed in CD3CN/D20 (95 5). Oxidation of the tetrathiafulvalene unit of the guest occurs after the addition (step 2 in Fig. 10.8) of three equivalents of I2. The resulting monocationic guest... 

Monoelectronic oxidation of the TTF unit is accompanied by the circumrotation of the desymmetrized ring through the cavity of the tetracationic cyclophane. Indeed, after oxidation, the newly formed monocationic tetrathiafulvalene unit... 

Figure 30. Circumrotation of the macrocyclic polyether component of the [2]catenane can be controlled oxidizing/reducing reversibly the tetrathiafulvalene unit [59. ...

M. White, A.J.P. Williams. D.J. A chemically and electrochemically switchable [2]catenane incorporating a tetrathiafulvalene unit. Angew. Chem., Int. Ed. 1998, 37. 

According to these principles, compound 57 was synthesized and electropolymerized in spite of the problems posed by the presence of an easily oxidized tetrathiafulvalene unit [152,153]. Other bithiophenic precursors 58 and 59 have been successfully electropolymerized [154], while polymers derived from precursors 60 [155,156] or 61 [157] have been prepared by chemical coupling. 

A tetrathiafulvalene unit has been incorporated into the macrocycle 56 to modify its electrochemical (redox) properties [108],... 

One line of interest in catenanes is to use them to study details of electron transfer, by having an electron donor in one ring, an electron acceptor in another (Figure 4-12). The first step in this programme was the synthesis of a [2]-catenane with a tetrathiafulvalene unit incorporated into one of the rings. The required catenane... 

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