Ferrocene electron acceptor/donor

Shumate WJ, Mattem DL, Jaiswal A, Burgess J, Dixon DA, White TR, Honciuc A, Metzger RM (2006) Spectroscopic and rectification studies of three donor-sigma-acceptor compounds, consisting of a one-electron donor (pyrene or ferrocene), a one-electron acceptor (perylenebisimide), and a C19 swallowtail. J Phys Chem B110 11146-11159... 

Carbocations as electron acceptors in aromatic EDA complexes 192 Bis(arene)iron(II) complexes with arene and ferrocene donors 198 Carbonylmetallate anions as electron donors in charge-transfer salts 204 Aromatic EDA complexes with osmium tetroxide 219... 

Ferrocene has been widely investigated as an electron donor and its electron donating ability can be tuned by redox reactions. As anticipated, when a ferrocene unit is covalently connected to an electron acceptor moiety that shows intrinsic fluorescence, the fluorescence of the acceptor moiety would be largely quenched because of the photoinduced electron transfer between ferrocene and the fluorescent acceptor. For instance, triad 15 that contains perylene diimide flanked by two ferrocene moieties, shows rather weak fluorescence due to the photoinduced electron transfer between perylene diimide and ferrocene units. Either chemical or electrochemical oxidation of ferrocene unit lead to fluorescence enhancement. This is simply because the electron donating ability of ferrocene is reduced after oxidation and accordingly the photoinduced electron transfer is prohibited. In this way, the fluorescence intensity of 15 can be reversibly modulated by sequential electrochemical oxidation and reduction. Therefore, a new redox fluorescence switch can be established with triad 15.25... 

Much work has been undertaken to modify electrode surfaces with films which are themselves conducting. The most promising approaches involve organic charge transfer and radical ion polymers. Coordination chemistry has, to date, played little part in this work (a good recent review is available),67 but one example relating to ferrocene chemistry can be quoted. In this example a well known electron acceptor, 7,7, 8,8 -tetracyanoquinodimethane (TCNQ 27), is modified and incorporated into polymer (28) in which the iron(II) of the ferrocene unit is the electron donor. The electrical conductivity of such a film will depend on partial electron transfer between ion and TCNQ centres as well as on the stacking of the polymer chains. The chemistry of other materials, based on coordination compounds, which have enhanced electrical conductivity is covered in Chapter 61. 

Similarly, the pyridyl fullerenes 30 and 31 also axially bind to ZnNcCBu)4 (28) to form supramolecular triads in which the zinc(II) naphthalocyanine acts as an electron donor, the pyridyl fullerenes act as primary electron acceptors, and either the ferrocene (Fc) or iV,iV-dimethylaminophenyl (DMA) moiety serves as a second electron donor [43], Fig. 2 shows the optimized structures of the resulting triads calculated by density functional theory (DFT), showing that the three components are arranged in a linear fashion. The binding constants of these systems (7.4 x 104M 1 for [ZnNc( Bu)4] 30 and 10.2 x 104M 1 for [ZnNc( Bu)4] 31 in o-dichlorobenzene) determined by UV-Vis spectroscopy are comparable with... 

The relevance of the charge on an organometallic complex is dramatically underscored by the comparison of ferrocene (Cp2Fe), which is a powerful electron donor (121), with its isoelectronic analog bis(ben-zene)iron(II) dication (BZ2Fe2+), which is an effective electron acceptor... 

More recently, elegant mechanistic studies on intramolecular Meer-wein reactions by Beckwith et al. considerably extended the utility of diazonium salts. They showed that many electron donors could convert an arenediazonium cation into an aryl radical which cyclized in good yield to form dihydrobenzofurans and indolines. The final radical was functionalized as a halide, sulfide, or ferrocene. Thus, the credentials of diazonium salts as electron acceptors were well established, and the stage was set to investigate the interaction between diazonium salts and TTF. 

Pinzon, J.R., Plonska-Brzezinska, M.E., Cardona, C.M. et al. (2008) ScsNOCgo-ferrocene electron-donor/acceptor conjugates as promising materials for photovoltaic applications. Angewandte Chemie International Edition, 47, 4173 176. 

Kihara et al. [188] have introduced a series of redox reactions suitable for studying the electron transfer (8). These systems involved ferrocene or tetrathiafulvalene as electron donor or tetracyanoquinodimethane as electron acceptor in the organic solvent phase, and Fe(CN), Ce, Fe ", or Cr207 as electron acceptor, or Fe(CN)6 or hydroquinone as electron donor, in the aqueous phase. Since all these systems showed reversible behavior under the conditions of current-scan polarogra-phy, no kinetic- data have been reported. 

C-P-Im triad 49 was prepared in order to further investigate this phenomenon [184]. An electron acceptor moiety based on the 4,5-dinitro-l,8-naphthalenedicar-boximide system was used in this triad, as this imide is more easily reduced that pyromellitimide (—0.88 V versus ferrocene/ferrocenium as an internal reference, compared to —1.24 V for the imide moiety of 48), and can therefore serve as an acceptor for a wider variety of donors. Excitation of the porphyrin moiety of 49... 

Quinone modified polymeric electron transfer systems The redox mechanism of quinone (two electron-proton acceptor/donor) is pH dependent and somewhat more complicated than for ferrocene or osmium (one electron accepter/donor). However, quinones are naturally occurring redox mediators and therefore, many researchers have studied their application to biosensors [107-109]. 

The UV spectrum of ferrocene in CCl. contains a new strong and broad absorption band in the wavelength region from 300 to 390 nm (60,61). This new band is due to a charge-transfer complex formed between ferrocene and CCl (62,63) The iron atom serves as an electron donor and the chlorine atom as an electron acceptor. Under U7-irradiation the photochemical dissociation of this charge-transfer complex takes placet... 

There continues to be an enormous amount of activity in the area of PET, much of it directed towards the development of systems capable of delivering artificial photosynthesis. Many of these systems involve porphyrin units as electron-donors and thus it is appropriate to consider them in this section of the review. A number of new fullerene-porphyrin dyads have been reported. A pyrazolinofullerene (155) has been constructed which facilitates efficient PET when strong donors such as iV,Ar-diethylaniline or ferrocene are linked to the pyrazoline ring. A photosynthetic multi-step ET model (156) based on a triad consisting of a meso,meso- inked porphyrin dimer connected to ferrocene and Ceo as electron-donor and electron-acceptor, respectively, has been synthesized and its ET dynamics (Scheme 38) have been investigated using time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. ... 

Polymer formation can occur through a variety of reactions. Metallocene polyamides, polyethers, polyesters, polyhydrazides and polyurethanes have been synthesized through condensation reactions of 1,1 -difunctional metallocenes (typically ferrocene derivatives) with diacid halides (if the metallocene derivative contains functional electron-pair donor bases) and electron-pair donor bases (as diamines, hydrazines, diisocyanates, diols) if the metallocene derivative contains functional electron-pair acceptor acids . 

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