Ferrocene photoinduced electron transfer

Okayama, Japan. The synthetic procedures for S-D dyads and their reference compounds shown in Fig. 6 are illustrated in Fig. 7, where a naphthalene and a ferrocene moiety are used as an S and a D moiety, respectively. For comparison of photoinduced electron transfer rates between a single alkyl chain and a triple alkyl chain as the spacers of the S-D dyads with the same length of four-carbons, S-D dyads with a rigid spacer with a bicyclo[2.2.2]octane were synthesized [39]. The synthetic procedure for the S-D dyads with the rigid spacer is also shown in Fig. 8 [39], Other amphiphilic compounds and chemicals were commercially available. 

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... 

B. Photoinduced Electron Transfer in Bis(arene)iron(ll) Complexes with Ferrocene and Aromatic Donors... 

The two intermediates are clearly the result of photoinduced electron transfer from the ferrocene donor to the 6w(arene)iron(lI) acceptor, which constitutes the first reaction step toward deligation (Eq. 37). 

Photophysical properties of porphyrin-Cjo dyads (9) have also been smd-ied systematically by Imahori, et al. [110]. In addition, a picosecond transient absorption study of a series of ferrocene-CgQ dyads for distance dependent photoinduced electron transfer has been carried out by Guldi et al. [111]. 

The design of covalently linked donor-fullerene systems capable of undergoing photoinduced electron-transfer processes has been widely studied as a result of the remarkable photophysical [35] and electronic [36] properties of fullerenes. Porphyrins, phthalocyanines, tetrathiafulvalenes, carotenes, and ferrocene [37] have been covalently attached to the fullerene sphere, usually as pyrrolidine[ 60] fullerene derivatives by 1,3-dipolar cycloaddition reactions. 

Various fullerenes and C70) were coordinated to zinc(II) and mag-nesium(II) porphyrins via functionalized pyridines or imidazoles (Fig. 7) by D Souza and Ito [10-22]. Both single-point [10,11] and two-point [12-14] binding strategies were employed, together with additional covalent functionalization of the porphyrins with ferrocene (Fc) [10] or boron dipyrrin (BDP) [16]. Similar systems were also studied by Guldi, Diederich, Nieren-garten and Schuster, and the results on the intermolecular and supramolecu-lar photoinduced electron transfer (PET) processes of fullerene-porphyrin and phthalocyanine systems were reviewed recently [23,24]. Since PET is... 

T. Nakamura, H. Kanato, Y. Araki, O. Ito, K. Takimiya, T. Otsubo and Y. Aso, Effects of extension or prevention of TT-conjugation on photoinduced electron transfer processes of ferrocene-oligothiophene-fullerene triads, J. Phys. Chem. A, 110, 3471-3479 (2006). 

Rajkumar, G. A. et al. Prolongation of the lifetime of the charge-separated state at low temperatures in a photoinduced electron-transfer system of [60]fullerene and ferrocene moieties tethered by rotaxane structures. J. Phys. Chem. B 110, 6516-6525, 2006. 

Sandanayaka, A. S. D. et al. Photoinduced electron transfer processes in rotaxanes containing [60]fuller-ene and ferrocene Effect of axle charge on light-induced molecular motion. Aust. J. Chem. 59, 186-192, 2006. 

The radical anion 60 can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines vide supra), ferrocenes, tetrathiafulvalenes, and thiophenes. In homogeneous systems, back electron transfer to the reactant pair plays a dominant role resulting in an extremely short hfetime of Qo In these cases, no net formation of is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors. - Selective one-electron reduction of Qq to Cjo takes place by the irradiation of Qq in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicotinamide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 10). The formation of Qq confirmed by the observation of the absorption band at 1080 nm in the NIR spectrum assigned to the fullerene radical anion. 

Fig. 13.16 Multi-step photoinduced electron [50] and (b) ferrocene-meso, meso-linked transfer in (a) a ferrocene-zinc porphyrin-free porphyrin trimer-fullerene pentad [Fc-base porphyrin-C60 tetrad (Fc-ZnP-H2P-C60) (ZnP)3-C60] Ar = 3,5-Bu 2C6H3 [51].

In the next example, a mixed SAM is discussed which aims to utilize photoinduced energy and electron transfer processes to create a photocurrent in an approach which is reminiscent of the natural photosynthetic process. Figure 5.33 illustrates the molecular structures of the components of interest, i.e. the molecular triad ferrocene-porphyrin-fullerene (Fc-P-C6o) and a boron dipyrrin thiol (BoDy) [67]. Mixed monolayers were generated by coadsorption onto vacuum-deposited gold... 

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