TTF-crown ethers

The construction of macrocyles containing TTF units has received considerable attention since such molecules may act as a host in host-guest chemistry. Planar derivatives containing the TTF-crown ether 971 and TTF-crown thiaether 972 have been investigated for potential use as electroactive cation sensors <2000CSR153>. 

Several TTF-crown ether derivatives, such as LI, have been prepared and investigated as potential metal ion sensor systems [180]. Cyclic voltammetry studies revealed in all cases two one-electron reversible oxidation steps with Ei/2( ) = 0.48 and E]/2(i) = 0.64 V (vs. SCE), respectively. The addition of controlled amounts of metal ions such as Li", Na", K", and Ag leads to shifts of Ei/2H) up to 80 mV toward more anodic potentials, as expected for a repulsive coulombic interaction. The magnitudes of the observed shifts are dependent on the hole size in the crown ether and on the concentration of the metal ion, up to a certain limit. The synthesis and spectroscopic and electrochemical studies of unsym-metrical annelated TTF-crown ethers bound to Na, Ag", and Ba " have been recently described [181]. 

Intermolecular interactions between Pc moieties and electron-donor or electron-acceptor units other than Pcs have also been exploited in order to promote the organization in Pc-based systems. One of the examples has been reported by Amabilino, Rowan, and Nolte, who prepared a TTF-crown ether-substituted Pc 8 (Figure 6a), which was able to self-organize in solution mainly because of intermolecular interactions between the TTF and the Pc moieties as inferred from UV-vis studies. TEM analysis of the gel... 

Figure 6 Tetrathiafulvalene (TTF)-crown ether-substituted Pc 8. Transmission electron microscopy showing the formation of chirai helical fibers of P and M helicity. (Reproduced from Ref. 22. Royal Society of Chemistry, 2005.)...

The first three-dimensional macrobicyclic TTF derivatives have been obtained <96CC615> and work on TTF-containing crown ethers and thioethers has continued <96LA551, 96JCS(P1)1995> with structures of this type being used to obtain the first TTF-containing... 

Several studies on systems incorporating TTF and C60 have appeared including the formation of a BEDT-TTF l3 C60 complex <00CC2357>, covalently bound TTF-C60 compounds and a C o ITF-crown ether triad . 

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... 

CV) experiments [9a, 9b], the bielectronic oxidation process occurs on the TTF unit at +0.80 V vs. saturated calomel electrode (SCE), and the oxidation of the DNP ring system is strongly displaced toward +1.60 V vs. SCE, compared to that of the free crown ether (+1.17 V vs. SCE). The dramatic increase in the oxidation potential of the DNP ring system indicates that it is encircled by the tetracationic cydophane after the oxidation of the TTF unit. 

Two types of oxa-thiacrown ethers containing tetrathiafulvalene (TTF) units have been reported by the Bryce and Salle groups. One is represented by the dithiatetraoxa-18-crown-6-ether derivatives substituted at the 2,3-positions of the TTF unit 98-104, and the other is derived from the tetrathiapentaoxa-24-membered crown ether derivatives annelated in the 2,7- (or 2,6-) positions of the TTF unit 105-107. 

Dendrimers with up to 96 redox-active TTF moieties on the periphery, which allow the generation of polycationic species bearing up to 192 positive charges on the surface, were incorporated into electrodes. These dendrimer-modified electrodes find application in electrochemical sensing of metal cations (i.e., Ba ), thanks to the grafting of crown ether/TTF units on the periphery of dendrimers < 2001AGE224>. 

Fig. 28. Synthesis of the electrochemically switchable [2]catenane 21-4PF6. Obtained in 55% yield from the naphthalene-containing dibromide and bis(methanol)TTF, the crown ether 20 can be catenated under standard conditions to give the [2]catenane 21-4PF6 in 23% yield. As well as the expected n-n interactions, a strong [C—H- O] hydrogen bond is also observed...

Fig. 29. The UV-Vis spectrum of [2]catenane 21-4PF6 shows - a by virtue of a strong charge transfer band at 830 nm - exclusive occupancy of the cyclophane cavity by the TTF unit, b Addition of one equivalent of Fe(Cl04)3 oxidizes the TTF unit to its radical cation, which results in the circumrotation of the crown ether, such that the 1,5-dioxynaphthalene unit resides within the cyclophane s cavity, as indicated by the appearance of a charge-transfer band at 515 nm. c Addition of a further equivalent of iron perchlorate yields the TTF dication which remains outside the cavity. Chemical reduction of the TTF dication back to its neutral form yields the [2]catenane in which the TTF resides exclusively within the cyclophane s cavity...

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