Redox properties conjugate systems

The quiaones have excellent redox properties and are thus important oxidants ia laboratory and biological synthons. The presence of an extensive array of conjugated systems, especially the a,P-unsaturated ketone arrangement, allows the quiaones to participate ia a variety of reactioas. Characteristics of quiaoae reactioas iaclude nucleophilic substitutioa electrophilic, radical, and cycloaddition reactions photochemistry and normal and unusual carbonyl chemistry. 

The question of the contribution of the benzene rings to the indigo chromogen led to a search for the basic chromophore. Consecutively removing parts of the mesomeric system leaves a cross-conjugated structure 7 that, as the basic chromophore, still exhibits the typical deep color and redox properties of indigo. 

Extended conjugated systems of jr-electrons make these compounds promising candidates for various elecfronic devices [49, 50] and solar cell compo-nenfs [51,52]. These macrocycles provide a variefy of subsfifufion sifes which can be used fo create compounds with controlled electron donor/acceptor properties [53, 54]. In nature, metal-containing macrocycles are present as central structural units in many substances involved in biochemical redox reactions [55]. 

In the conjugate 169, for coupling the anion-receptor ability of the calix[4]pyrrole system to the redox properties of TTF core, one TTF unit has been directly annulated to the upper rim of calix[4]pyrrole. This... 

Ferrocene-functionalized oligothiophenes are interesting redox functional systems, in which the ferrocene is a donor as well as the oligothiophene backbone, and therefore demonstrate unique redox properties. As examples, structures 2.162 and 2.163 are shown (Chart 1.34) in which either ferrocenes are connected to the termini of the oligothiophene or represent the core for the conjugated co-oligomers [255, 256]. These systems play a role as unique redox-active agents and are described in detail in Chapter 5. 

As synthetic chemists desired to tune the optoelectronic and redox properties of conjugated polymers in a fine manner, more complicated conjugated systems were required. The two fused heterocycles-substituted polythiophenes 16 and 17 (Chapter 18) illustrate this as electron-poor imine functionality in 16 brings donor-acceptor character to the material, while the more electron-rich thio-based system 17 provides for especially easy oxidation. Polymerization of these complicated bis-2-thienyl monomers by electrochemical methods paves the way for fundamental structure-property relationships to be understood, ultimately directing the synthetic chemist towards soluble polymers (Chart 1.6). 

Other prominent sites for electrophilic addition are non-bonding electron pairs as they are present in many heteroatom-containing organic molecules. One example has already been mentioned, namely the RS conjugation with the sulfur anion function in thiolate. As formulated in the back reaction of equilibrium (14) this yields the three-electron bonded disulfide radical anion, (RS SR)in which the unpaired thiyl electron couples with the free p-electron pair at the thiolate sulfur. In this context, a significant consequence emerges with respect to the overall redox properties of such a system. As has been stated already, the... 

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