Photo-induced electron transfer process

Although the correlation between ket and the driving force determined by Eq. (14) has been confirmed by various experimental approaches, the effect of the Galvani potential difference remains to be fully understood. The elegant theoretical description by Schmickler seems to be in conflict with a great deal of experimental results. Even clearer evidence of the k t dependence on A 0 has been presented by Fermin et al. for photo-induced electron-transfer processes involving water-soluble porphyrins [50,83]. As discussed in the next section, the rationalization of the potential dependence of ket iti these systems is complicated by perturbations of the interfacial potential associated with the specific adsorption of the ionic dye. 

FIGURE 14. Photo-induced electron transfer process. 

The current detailed understanding of photo-induced electron transfer processes has been advanced dramatically by the development of modern spectroscopic methods. For example, the application of time-resolved optical spectroscopy has developed from modest beginnings (flash-phyotolysis with millisecond resolution) [108,109] to the current state of the art, where laser spectroscopy with nanosecond resolution [110-113] must be considered routine, and where picosecond [114-116] or even femtosecond resolution [117] is no longer uncommon. Other spectroscopic techniques that have been applied to the study of electron transfer processes include time-resolved Raman spectroscopy [118], (time resolved) electron spin... 

Extensive studies have been made of photo-induced electron-transfer processes in amphiphilic micelles (Turro et al., 1980). The micelle structure is considered to be spherical, having an inner hydrocarbon core and an outer, highly charged and densely packed Stern layer which is surrounded by a charged but less densely packed Gouy-Chapman layer. 

Phthalimides participate in a number of photo-induced electron-transfer processes. They have been found to react with alkenes with the formation in some cases of oxetanes, e.g. [140], and ring expansion products [141] (Scheme 32) (Mazzocchi et al., 1978a, 1979 Maruyama and Kubo, 1978a). The reaction can also be carried out intramolecularly (Maruyama et al., 1978 ... 

During the past decade, photochemical methods have been widely used to investigate electron transfer processes in DNA [11 15], Three distinct types of photo-induced electron transfer processes have been identified ... 

The special features of Co-cage complexes can be exploited in reactions which involve photo induced electron transfer processes [46-54], Photoexcitation of Co complexes in their LMCT band usually leads to an excited state that formally is a Co" species. The subsequent efficient decomposition can be interpreted in terms of lability of Co" complexes. In contrast, in the case of [Co " (cage)] complexes such... 

An examination of the photo-induced electron transfer processes between the quinone (268) and multifunctional porphyrins has been carried out. Chloranil has been used as an electron accepting sensitizer in the presence of the silylenols (269) and (270). The reactions can be carried out in both methylene chloride and acetonitrile and result in the conversion of the enols into the corresponding ketones. Other studies on the same systems have shown that the outcome of the irradiation at X > 380 nm can be influenced by solvent polarity and by added salt. ° Time-resolved spectroscopy has been used to study the excited singlet state of /7-chloranil. ... 

We have previously shown that when PPV is self-assembled with specific electronically active polyanions such as poly(thiophene acetic acid) (PTAA) or sulfonated fiillerenes (S-C60 )(7), the photoluminescence of the PPV is essentially completely quenched by the polyanion. The mechanism of this quenching is believed to be due to a photoinduc electron transfer process taking place between the excited PPV and the adjacent electroactive polyanion molecules. The quenching process, in this case, is not associated with a Forster type energy transfer since in both cases, the required spectral overlap of a donor emission band with an acceptor absorption band is not fulfilled. In addition, photo-induced electron transfer processes have previously been confirmed in PPV/C60 systems and can be exploited to fabricate thin film photovoltaic devices (77). In order to mediate this electron transfer process, we have constructed multilayer heterostructures in which the PPV donor and the polyanion electron acceptor are separated from each other with electronically inert spacer layers of known thickness. In addition to allowing studies of the electron transfer process, such structures provide important insights into the thermal stability of the multilayer structure. The "spacers" used in this study were bilayers of SPS/PAH with an experimentally determined bilayer thickness of 30 +/-5 A. 

The discussion so far has focused on reactions in the Marcus-normal region , for which lAGoA I/Xr < 1. The regime in which A(jDA /Xr> 1 is most readily accessed by means of photochemical or pulsed radiolysis techniques. Photochemical techniques are very powerful, but they usually involve an initial photo-induced electron transfer process, and this requires pre-assembly of the reactants. In the context of outer-sphere electron transfer processes, such pre-assembly involves ground state ion pairs. 

Isoda, S., Y. Hanazato, K. Akiyama, S. Nishikawa, and S. Ueyama (2003). Photoelectrical properties based on photo-induced electron transfer process in flavin-porph5n in hetero-type Langmuir-Blodgett films. Thin Solid Films 441, 277-283. 

S. Knorr, A. Grupp, M. Mehring, G. Gruhe and F. Effenberger, Photo-induced electron-transfer processes in (anthracene-) quinquethiophene-fuUerene diads and triads, J. Chem. Phys., 110, 3502-3508 (1999). 

This photo-induced electron transfer process among the molecules may be utilized as fluorescence switching. A fluorophore having a macrocyclic unit, on irradiation... 

Photoirradiation of benzene and its derivatives with alkenes give ortho-, meta-, para-cycloaddition products. In most cases, either meta- or orr/io-adducts are obtained as major products [5]. Bryce-Smith and Gilbert suggested a prefulvene type diradical intermediate mechanism (Path A) for the weta-adduct [6], whereas Morrison and Srinivasan groups [7, 8] proposed the exciplex mechanism (Path B) for the formation of these adducts (Scheme 9.1). The exciplex intermediates undergo photo-induced electron transfer processes between donor (D) and acceptor (A) to produce radical ion pairs as intermediates, stabilized by coulombic interactions to give adducts [9]. 

Aromatic amine 73 undergoes photo-induced alkylation with pentafluoro iodobenzene to give 74 and 75 through a radical coupling mechanism in a photo-induced electron transfer process [61]. 

Sabbatini and Balzani (1985) have reported a study of the photo-induced electron-transfer processes involving (2,2,1) Eu cryptates. Both Eu(II) and Eu(III) cryptates are suitable as redox quenchers of excited-state molecules, e.g., ruthenium complexes ... 

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