Ferrocene oligomers

III. Ferrocene Oligomers and Polymers with Conjugated Spacers... 

A. Dependence of Redox Properties on the Spacers in Conjugated Ferrocene Oligomers... 

B. Redox, Optical, and Photoisomerization Properties of Azo-Bridged Ferrocene Oligomers... 

Table IV lists the redox potentials of conjugated ferrocene oligomers (mainly dimers with a single bridge). Potential values are denoted against different reference electrodes as given in the references. The values can be primarily compared using the relationship mentioned in the footnote of the table, although care should be taken with some errors derived from junction potentials which depend on experimental conditions. There have been several reports on the quantitative estimation of structural factors affecting internuclear electron delocalization.

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

Strong MLCT bands appear in the neutral form of azo-bridged ferrocene oligomers, as noted above. The absorption of the MLCT band at 534 nm diminishes, and a new band appears and increases at 672 nm with the oxidation to 25+. The new band can be assigned to a ligand-to-... 

As far as the electrochemical properties are concerned, a different behavior is exhibited by directly linked ferrocene oligomers in which metal oxidation occurs in separate steps because of a strong electronic interacting among the metal centers. The biferrocene (BFc) moiety, for example, can exist in three oxidation states, that is, the neutral Fe2(II,II), the mixed-valence cationic Fe2(II,III)+, and the dicationic... 

Ferrocene compounds and polymers have been used as micelle-forming agents in electrochemical processes for producing organic films usable in electronic materials such as color filters. To increase the concentration of ferrocene in these processes, an ferrocene oligomer having gelling properties has been prepared. 

II. REDOX, OPTICAL, AND PHOTOCONDUCTING PROPERTIES OF CONJUGATED FERROCENE OLIGOMERS AND POLYMERS... 

Very recently, this approach was met with success, and a series of novel ferrocene-oligomers 69-72 and polyferrocenyl peptide 73 were reported (Scheme 12.17).61 Preliminary measurements on the polymeric material indicate a globular structure in aqueous solution and a surprisingly high molecular weight. However, the polymeric material still awaits its full characterization, in particular with respect to its electronic properties. 

Scheme 12.17 The synthesis of a series of novel ferrocene-oligomers 69-72 and polyferrocenyl peptide 73, after Boc-deprotection of l,n -bis(Boc-amino)ferrocene, it was coupled to ferrocene-1, /f -dicarbonyl chloride in THF, using the polycondensation protocol.

Fig. 3.35 Proposed structures of ferrocene oligomers (a) in less polar solvent and (b) in polar solvent.

Arnold et al. reported in 1988 [68] the synthesis of oligomeric or low molecular-weight polymeric metallocenes (M = Fe or Ru) in which the separate metallocene units are held proximate and face to face by the bridging peri-substituted naphthalene rings, 17. Cyclic voltammetry of the ferrocene oligomers shows... 

Nishihara, H. Redox and optical properties of conjugated ferrocene oligomers. Bull... 

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