Fullerenes charge-transfer reactions

Recently, photochemical and photoelectrochemical properties of fullerene (Cto) have been widely studied [60]. Photoinduced electron-transfer reactions of donor-Qo linked molecules have also been reported [61-63]. In a series of donor-Cfio linked systems, some of the compounds show novel properties, which accelerate photoinduced charge separation and decelerate charge recombination [61, 62]. These properties have been explained by the remarkably small reorganization energy in their electron-transfer reactions. The porphyrin-Qo linked compounds, where the porphyrin moieties act as both donors and sensitizers, have been extensively studied [61, 62]. 

Compared with the variety of existing carbon or nitrogen nucleophiles that were subjected to nucleophilic addition to there are few examples for phosphorus nucleophiles. Neutral trialkylphosphines turn out to be to less reactive for an effective addihon to Cjq even at elevated temperatures [114], Trialkylphosphine oxides show an increased reactivity. They form stable fullerene-substituted phosphine oxides [115] it is not yet clear if the reaction proceeds via a nucleophilic mechanism or a cycloaddition mechanism. Phosphine oxide addition takes place in refluxing toluene [115], At room temperature the charge-transfer complexes of with phosphine oxides such as tri-n-octylphosphine oxide or tri-n-butylphosphine oxide are verifiable and stable in soluhon [116],... 

A similar approach was used in grafting Cjq onto a pregenerated lithiated polyethylene surface [121]. A polyethylene film with terminal diphenylmethyl groups was deprotonated with BuLi to yield an anionic polyethylene surface that was treated with Cg0 and quenched with methanol. The incorporation at the polyethylene surface was determined by XPS, UV/Vis and fluorescence spectroscopy. This reaction also works for polyisopropene, polybutadiene [69], poly(vinylbenzyl chloride) or poly(N-vinylcarbazole) PVK [54] with BuLi or NaH as a base. Charge-transfer interactions in the soluble fullerene-PVK derivative between the positively charged carbazole and Cjq lead to an enhanced photoconductivity compared with PVK [54]. 

In addition to quinone reduction and hydroquinone oxidation, electrode reactions of many organic compounds are also inner-sphere. In these charge transfer is accompanied by profound transformation of the organic molecules. Some reactions are complicated by reactant and/or product adsorption. Anodic oxidation of chlorpro-mazine [54], ascorbic acid [127], anthraquinone-2,6-disulfonate [128], amines [129], phenol, and isopropanol [130] have been investigated. The latter reaction can be used for purification of wastewater. The cyclic voltammogram for cathodic reduction of fullerene Cm in acetonitrile solution exhibits 5 current peaks corresponding to different redox steps [131]. 

Dunsch and co-workers (Bartl et al., 1996 Dunsch et al., 1995, 1997 Petra et al., 1996) studied electron transfers in metallofullerenes by CV coupled with in situ ESR experiments. The electron transfer fo fhe endo-hedral La Cg2 molecule studied by this method gives evidence of a charge in the electronic state of the fullerene the electrochemical reaction in the anodic scan causes the formation of La Cs2", and during the cathodic scan the spin concentration decreases as the La + C82 structure formed by reduction is not paramagnetic. 

Fullerenes are excellent electron acceptors. The early examples for the high electron affinity of fullerenes include efficient nucleophilic addition reactions of fullerenes with electron donors such as primary and secondary amines. Since then, there have been many studies of electron transfer interactions and reactions involving fullerene molecules. It is now well established that both ground and excited state fullerene molecules can form charge transfer complexes with electron donors. The photochemically generated fullerene radical anions as a result of excited state electron transfers serve as precursors for a wide range of functionalizations and other reactions. 

Ground state and C70 also react readily with a tertiary aliphatic amine triethylamine (TEA) at high TEA concentrations [87]. The reaction of Cgg and TEA results in the formation of a new absorption band in the blue region, which was initially mistaken as the absorption of a Cgg-TEA charge transfer complex [85,87]. The reaction products appear to be complicated as well, whose separations and identifications remain to be completed. In the photoexcited states of fullerenes, however, reactions with TEA are more efficient even at low TEA concentrations [66,71,118]. The reaction mixture can be divided into two fractions in terms of the solubility in toluene. The relative quantities of the two fractions are somewhat dependent on irradiation time. 

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