Electroactive donor

Fig. 1 Chemical structures of TTF, BEDT-TTF and BETS electroactive donor molecules...

Fig. 5 Chemical structures of the two electroactive donor molecules functionalized with pyridine heterocycle...

Electroactive donors, such as TTF or triarylpyrazoline, can be bound in high yield to polymeric matrices. The TTF linear polymers show interesting cooperative properties (i.e., ion-radical cluster formation) that is not observed for the isolated monomers in solution or the low coverage polymers. Furthermore, thin solid films of these donors bound to cross-linked polymer backbones display remarkably facile charge transport through the film bulk which is accompanied by dramatic and reversible optical changes. 

The magnitudes of the standard redox potentials (e.g., —1.56 and -I-1.53 V vs. SCE in acetonitrile) and the relatively low energy of excited Mo6Clfj (1.9eV) have also made possible observation of ECL from the annihilation of Mo6Cl] 4 and MofiClf with a variety of electroactive donors D (aromatic amines forming stable... 

Electron donor-acceptor (EDA) stacks have been accessed by Percec et al. [90] using partially fluorinated dendrons (Fig. 14) to form LC columnar phases. The self-assembly of the dendrons is primarily driven by phase segregation of the fluorinated chains and the aromatic units. Functionalization of the dendrons at their apex with either an aromatic electroactive donor (29a) or an acceptor (29b) group yields LC columnar structures, further aided by the additional interaction between the aromatic units, which have optoelec-... 

Fig. 8. Different photo-and electroactive donor-aceptor (TTF- Ceo) supramolecular dyads based on complementary guanidinium and carboxylate units.

From a synthetic point of view, the Donor-Acceptor (D-A) route is the most utilised method in terms of diversity in synthetic possibilities allowing the presence of both electroactive donor groups and electron deficient acceptor units in the polymer backbone. By this way, the HOMO of the donor contributes to the polymer s valence band, and the... 

The slow protonation rate of the conjugated anion of the sulphone (1st step) leads to the obtainment of a pseudo one-electron process. However, no self-protonatiori process exists in the presence of an excess of a proton donor of lower pKa than that of the electroactive substrate and Figure 6a, curve 2 shows evidence for a two-electron step. Full substitution on the a carbon, as in the case of phenyl 2-phenylbut-2-yl sulphone, does not allow one to observe any deactivation (Figure 6b, curve 1). It is worth mentioning that cathodic deactivations of acidic substrates in aprotic solvents are rather general in electrochemistry, e.g. aromatic ketones behave rather similarly, showing deprotonation of the substrate by the dianion of the carbonyl compound39. 

It has been found50 that such a multielectron step does not exist with 58, which exhibits a classical two-electron scission. In general, allylic sulphones (59) without an unsaturated system in a suitable position are not reducible. Thus, they do not exhibit a cathodic step in protic solutions. However, in aprotic media the isomerization may be base catalyzed, since small amounts of electrogenerated bases from electroactive impurities, even at low concentration, may contribute to start the isomerization. Figure 10 shows the behaviour of t-butyl allylic sulphone which is readily transformed in the absence of proton donor. On the other hand, 60 is not isomerized but exhibits a specific step (Figure 10, curve a) at very negative potentials. 

The basic condition for electron transfer in cathodic processes (reduction) to an electroactive substance is that this substance (Ox) be an electron acceptor. It must thus have an unoccupied energy level that can accept an electron from the electrode. The corresponding donor energy level in the electrode must have approximately the same energy as the unoccupied level in the substance Ox. 

On the other hand, in oxidation processes, the electroactive substance Red must have the character of an electron donor. It must contain an occupied level with energy corresponding to that of some unoccupied level in the electrode. Oxidation occurs through transfer of electrons from the electroactive substance to the electrode or through the transfer of holes from the electrode to the electroactive substance. 

Fig. 5.4 Electron transfer in vacuo and in solution. (A) When the electron donor and the proton acceptor have very different corresponding energy levels the electron transfer is impossible. (B) When the reaction partners are present in a solution, then a change in their configuration can bring their corresponding energy levels close together (dashed line) so that electron transfer is possible. (C) An analogous situation is in the system of an electrode and an electroactive particle in solution...

The quinoxaline 100, with self-contained donor-acceptor properties, has potential in optoelectronic <06JACS10992>. Electroactive dendrimeric bis-quatemary salts have been prepared by direct quatemisation of pyrazine using dendrimeric benzyl bromides <06TL4711>. 

Electroactive 3-(N-phenylpyrazolyl)fullereno[l,2-r/]isoxazolines have been synthesized by using 1,3-dipolar cycloaddition of pyrazole nitrile oxides, generated in situ, to Cgo at elevated temperature or microwave irradiation. The cyclic voltammetry measurements show a strong donor pyrazole ring, and a better acceptor ability of the fullerene moiety than the parent C60 (538). Treating fullerene Cgo with mesitonitrile oxide in toluene gives fullerene-nitrile oxide adduct, which is supposed to be useful for electrical and optical components (539). 

As already seen for catenanes 134+ andl44+ (Fig. 13.15),ongoingffomseparated molecular components 16,124+, or 154+ to their catenanes substantial changes in the electrochemical behavior are expected because the electroactive units incorporated in the cyclophanes and macrocycle are engaged in donor-acceptor interactions and occupy spatially different sites. 

---