TTF units

The crystal structure consists of TTF layers in the (002) planes which alternate with inorganic Cu(hfac)2 layers in the (001) planes. These two layers are linked by conjugated bridge (Fig. 10a). Figure 10b focuses on the organic plane the TTF units form dimers with the shortest S—S contact equal to 3.593(3) A. In one dimer, each TTF belongs to two different complexes with copper ions lying in two... 

With the objective to enable long-lived charge-separated CgQ-complexes (also Section 4.2) TTF and extended TTF were bound via [3-1-2] cycloaddition with different spacer-lengths (Rj) (Figure 4.12) [215, 252-257]. In these C q-TTF dyads as well as in a bis-tetrathiafulvalene-Cgo triad no significant interaction between the TTF units and the CgQ-moiety in the ground state could be observed. 

Chemical oxidation of the TTF groups in compounds 34 and 35 has been achieved by reaction with an excess of iodine in dichloromethane solution, leading to new low-energy absorptions in the UV/visible spectra which are diagnostic of TTF cation radicals the broad absorption at = 830 nm for the iodide salt of 35 suggests the formation of aggregated TTF species. A charge transfer complex formed by 35 and tetracyano-p-quinodimethane (TCNQ) has been isolated as an insoluble black powder. The stoichiometry is (35), (TCNQ)3 (i.e. 8 TTF units 3... 

The related pentakis-TTF derivatives 41, synthesized by Becher et al. by reaction of tetraiodide 39 with four equivalents of the thiolate anion liberated upon treatment of 40 with cesium hydroxide (Scheme 9), displayed qualitatively similar redox behavior to 38 with noninteracting TTF units. The attachment of branched multiredox wedges (e.g. 32) to the tetrathio-TTF core should provide interesting systems in which a central TTF unit may be shielded by the outer layers and should oxidize more readily. 

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... 

TTF-based D-A systems have been extensively used in recent years to play around photoinduced electron transfer processes. Typically, when an electron acceptor moiety that emits fluorescence intrinsically is linked to TTF (D), the fluorescence due to the A moiety may be quenched because of a photoinduced electron transfer process (Scheme 15.1). Accordingly, these molecular systems are potentially interesting for photovoltaic studies. For instance, efficient photoinduced electron transfer and charge separation were reported for TTF-fullerene dyads.6,7 An important added value provided by TTF relies on the redox behavior of this unit that can be reversibly oxidized according to two successive redox steps. Therefore, such TTF-A assemblies allow an efficient entry to redox fluorescence switches, for which the fluorescent state of the fluorophore A can be reversibly switched on upon oxidation of the TTF unit. 

V,/V-Dimethylamino)benzonitrile (DMABN) and its derivatives, as a class of organic donor-acceptor compounds, exhibit dual fluorescence, one related to the local excited state ( B band) and the other ascribed to the twisted intramolecular charge transfer (TICT) state ( A band).17 As expected, compound 818 exhibits dual fluorescence, showing two fluorescence bands centered at 350 and 432 nm, which can be ascribed to the corresponding band (from the local excited state) and A band (from the TICT state), respectively. After oxidation of TTF unit in 8, the fluorescence intensity of A band decreases while that of band increases slightly. As expected, further reduction of TTF" + into neutral TTF unit leads to the restoration of the fluorescence spectrum of 8. Therefore, the dual fluorescence spectrum of 8 can be reversibly modulated by redox reactions of TTF unit in 8. 

It is interesting to note that the CD spectrum of 11 can be tuned by changing the oxidation states of the TTF units in the side-chains of 11. Polymer 11 shows reversible interconversion between three univalent and two very broad mixed-valence redox states that have different chiroptical properties. 

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 ... 

A polyrotaxane 29 possesses two electron-donating sites (TTF and hydro-quinone moieties) as stations in the polymer backbone, hence, the incorporated cyclic acceptor 28 moves by external stimuli and possibly two translational isomers (29a and b) would exist (Scheme 10) [106, 107]. The ratio between two isomers was reported to be very solvent dependent (Table 2), with a preference however for the hydroquinone moiety. In the CV measurement, it was also observed that the cyclic acceptor 28 moved from TTF to hydroquinone moiety along the chain of 29 upon oxidation of the TTF unit. 

The current-voltage curve was interpreted on the basis of the mechanism illustrated in Figure 17.15a, which is derived from the behavior of the same catenane 134+ in solution.116,117 Conformation I is the switch open state and conformation IV the switch closed state of the device. When 134+ is oxidized (+2 V), the TTF unit is ionized in state II and experiences a Coulombic repulsion inside the tetra-cationic cyclophane component, resulting in circumrotation of the crown ether and formation of conformation III (note that in solution at +2 V TTF undergoes two-electron oxidation and the dioxynaphthalene unit is also oxidized).116 When the voltage is reduced to near-zero bias, a metastable conformation IV is obtained... 

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