Dendrimers ferrocene polymers

Ferrocene-based Branched Polymers (Dendrimers). One of the topics in macromolecular chemistry is constituted by dendrimers, or hyperbranched macromolecules of tridimensional globular structure, the surface of which is characterized by a large number of functional groups, Scheme 4. Such functionalities impart to the molecules solubility, viscosity and thermal properties different from those of the common linear polymers.38c,d 44... 

Conceptually, dendrimers can be viewed as a class of well-defined monodisperse polymers with a globular structure. Dendrimers have been extensively reviewed,21 62 91-92 so we will take a very narrow view and briefly discuss dendrimers having a ferrocene core. Astruc s ferrocene-terminated dendrimers are reviewed elsewhere and will not be included in this brief discussion.92... 

An SECM feedback response to an electroactive polymer film can be controlled either by ET kinetics at the film-solution interface or by film conductivity. The contribution of lateral film conductivity to the effective ET rate measured by SECM was addressed in the recent study of polyaryl multilayers attached with ferrocenes [65] or ferrocene-terminated dendrimers [69] on unbiased carbon electrodes. In the latter study, the dependence of apparent ET rate constant, feei. on the generation of dendrimers (Table 6.2) was ascribed to the different efficiencies of electron transport inside and between dendrimers (Figure 6.22). Interestingly, the theory of the aforementioned triple potential step method predicts its potential to separately determine heterogeneous ET rate and lateral conductivity for a thin polymer film coated on an insulating surface [70]. 

The morphology of ferrocene-containing polymers has been examined in some detail. In the block copolymer of poly(ferrocenyldimethylsilane-b-dimethyl-siloxane) (PFDMS-b-PDMS) with a 1 6 block ratio long rodlike micelles are observed rather than spherical structures in a variety of PDMS-selective n-alkane solvents when the solutions are prepared at or near ambient temperature. The reasons for these observations are subsequently discussed in detail. A further series of mixed ferrocene cobaltocenium dendrimers have been obtained these have been prepared in the reaction of the acyl chlorides of ferrocene and the cobaltocenium PF " with polypropylene dendrimers. ... 

The electrochemical behavior of ferrocene-based polymers [15] and of complexes containing a large, well defined number of ferrocene-type units [16] had already been reported when several groups became interested in dendrimer research. In the past few years several dendrimers of different chemical nature and structure carrying ferrocene-type units in the periphery have been synthesized... 

Ferrocenyl-based polymers are established as useful materials for the modification of electrodes, as electrochemical biosensors, and as nonlinear optical systems. The redox behavior of ferrocene can be tuned by substituent effects and novel properties can result for example, permethylation of the cyclopentadienyl rings lowers the oxidation potential, and the chaige transfer salt of decamethylfer-rocene with tetracyanocthylene, [FeCpJ]" (TCNE], is a ferromagnet below = 4.8 K, and electrode surfaces modified with a pentamethylferrocene derivative have been used as sensors for cytochrome c These diverse properties have provided an added impetus to studies on ferrocene dendrimers. 

The same reasons for the interest in incorporating ferrocene units into polymers also provided motivation for the synthesis of dendritic macromolecules of well-defined size and structure containing ferrocenyl units. An important additional rationale for the construction of ferrocenyl dendrimers is provided by the fact that such macromolecules raise the possibility of combining the unique and valuable redox properties associated with the ferrocene nucleus with the highly structured macromolecular chemistry. This may provide access to materials of nanoscopic size possessing unusual symmetrical architectures, as well as specific physical and chemical properties which would be expected to differ from those of the ferrocene-based materials prepared to date. 

Finally, ferrocenyl units have been incorporated into the perimeter of dcndrimcric polymers by Astruc and coworkers.40 Gold nanoparticles form the core of the dendrimers, with the branched units with terminal ferrocene units coordinated to the gold surface via... 

We briefly mention here the use of the ferrocene/ferrocenium redox couple to mediate electron transfer on the oxidation (anodic) side, especially in derivatized electrode. This broad area has been reviewed [349]. For instance, polymers and dendrimers containing ferrocene units have been used to derivatize electrodes and mediate electron transfer between a substrate and the anode. Recently, ferrocene dendrimers up to a theoretical number of 243 ferrocene units were synthesized, reversibly oxidized, and shown to make stable derivatized electrodes. Thus, these polyferrocene dendrimers behave as molecular batteries (Scheme 42). These modified electrodes are characterized by the identical potential for the anodic and cathodic peak in cyclic voltammetry and by a linear relationship between the sweep rate and the intensity [134, 135]. Electrodes modified with ferrocene dendrimers were shown to be efficient mediators [357-359]. For the sake of convenience, the redox process of a smaller ferrocene dendrimer is represented below. 

The section commences with monosubstituted ferrocene derivatives, after which the influence of the substitution pattern on the formation and stability of liquid-crystalline phases for disub-stituted ferrocene derivatives will be discussed. Next, the influence of the three-dimensional structure of ferrocene on the mesomorphic properties will be highlighted, optically active ferrocene materials will be described and, finally, ferrocene-containing liquid-crystalline dendrimers will be introduced ferrocene-containing liquid-crystalline polymers will not be reported. Note that a review devoted to ferrocene-containing thermotropic liquid crystals has already been published. ... 

The synthesis and properties of star polymers and dendrimers functionalized with ferrocene units has attracted a great deal of attention. The synthesis of high-generation dendrimers functionalized with chiral ferrocenyl units in their structures has been reported. The chiroptical properties of this class of dendrimer was dependent on the number of ferrocenyl groups and their chemical environment, but not on their position within the dendrimer. Deschenaux has reported the synthesis of hquid crystalline ferrocene-based polymers prossessing an enantiotropic smectic A phase. Ferrocene-functionahzed cyclic siloxane (29) and silsesquioxane branched polymers have also been reported. A hyperbranched polymer with a cubic silsesquioxane core was used to mediate the electrocatalytic oxidation of ascorbic acid. 

A review article examines the literature up to 1999 on silicon- and amine-based ferrocene dendrimers and polymers and those immobilized on electrodes. In these dendrimers the ferrocene itself may be at the cote, the periphery, or be used as a spacer molecule. Some examples of these molecules are shown as 15-17. ... 

Chiral phosphorus-containing dendrimers which have ferrocene molecules at the periphery have been the subject of work by Majoral and co-workers. These materials will have obvious applications in catalysis. Layer-by-layer dendrimers, which are built up containing chiral ferrocenylphosphine molecules, have also been prepared, and their chiroptical and electrochemical properties have been investigated. A recent article covers the basic chemistry of ferrocene-containing liquid-crystalline polymers which stems from the extensive work of Deschenaux, who essentially pioneered the area. A ferrocene end-capped dendrimer has also been used in carbon monoxide sensing. The actual dendrimer, shown as 19, has 48 ferrocene molecules on the periphery. 

For longer polymers, adsorption and film formation can take place in organic solvents, which are good solvents for the neutral ferrocene-based species but bad solvents for the oxidized species [153, 154, 160-165]. In this case, even diblock copolymers precipitate on the electrode, without indication of the formation of micellar structures upon electrochemical switching [166-168]. Co-precipitation with carbon nanotubes onto electrodes has been achieved [169]. As a matter of fact, common solvents for both redox states are seldom available, unless the hydrophobic ferrocene units are complexed by cyclodextrins (in this case, water is a good solvent) [170, 171]. As another example, dendritic ferrocene-based polymers are sufficiently solubilized, even after oxidation in organic media (probably, the insoluble units are shielded in the interior of the dendrimers) [172]. Star-like... 

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