Photoelectron transfer,

Closely related reactions have been accomplished by photoelectron-transfer reactions of allylsilanes and benzylsilanes, and a similar mechanism involving the cation radical intermediate is suggested [29]. Chemical oxidation of allylsilanes [27] and ferrocenylsilanes [30] also cleaves the C-Si bond and mechanism of these reactions seem to closely relate to that of the electrochemical process. 

Whereas the previous methods for the synthesis of pyrrolo-oxazines were based on traditional ionic cyclization, the preparation of 7-rncthyltctrahydro-l //-pyrrolo[2,1 -c][l,4]oxazin K3//)-one 176 was reported using a new radical cyclization induced by photoelectronic transfer catalysis. This reaction is proceeding under very mild conditions and in neutral medium (Scheme 26). 

Interestingly, the correlation of the luminescence quenching by the mononucleotides and polynucleotides with the occurrence of a photoelectron transfer process examined by flash photolysis, has been found [73,95] for the whole series of Ru(II) complexes with TAP and HAT ligands discussed in Sect. 4.1. As will be developed in Sect. 5., this photoelectron transfer with polynucleotides is also connected to enhanced yield of strand breaks and the appearence of adducts on DNA. 

Photoelectron transfer is usually described by the so-called Foerster s cycle On transformation of a molecule into the excited state, the donor s IP is reduced by the value of the donor s excitation energy, and the acceptor s electron affinity increases by the value of the acceptor s excitation energy. 

Pileni, M. P. (1981). Photoelectron transfer in reverse micelles - photo-reduction of cytochrome-c. Chem. Phys. Lett., 81, 603-5. 

Radiolabeled [ C]SN003 27 has been evaluated as a photoelectron transfer (PET) ligand for CREj receptors <2006BMC4029>. 

Nafion membrane Size-quantized Fe203 particles prepared in situ Photoelectron transfer was examined 672... 

Cadmium lauryl sulfate micelles CdS Photoelectron transfer from nanosized (MS to viologens in aqueous micelles was investigated 96... 

Polyethyleneimine functionalized by N-(2-carboxyethyl) N -methyl-4,4 -bipyridinium, PEI-MVP2 + T10a Effective photoelectron transfer was observed 100... 

Efficient CdS size dependent photoelectron transfer 681, 682 was demonstrated... 

DNA mediated photoelectron transfer reactions have been demonstrated60 . Binding to DNA assists the electron transfer between the metal-centered donor-acceptor pairs. The increase in rate in the presence of DNA illustrates that reactions at a macromolecular surface may be faster than those in bulk homogeneous phase. These systems can provide models for the diffusion of molecules bound on biological macromolecular surfaces, for protein diffusion along DNA helices, and in considering the effect of medium, orientation and diffusion on electron transfer on macromolecular surfaces. 

This section described the fabrication of ITO electrodes modified with porphyrin-terminated M(tpy)2 complex wires by the stepwise coordination method, and it is demonstrated that the electronic nature of the molecular wire is critical to the photoelectron transfer from the porphyrin to ITO. These results suggest that the new facile fabrication method of molecular assemblies is effective in the construction of photoelectron transfer systems. The system could be upgraded by extending the wire length, embedding the redox potential step in the wire, increasing the photoreceptors in the wire, and/or incorporating donors and acceptors. 

Photoelectron transfer between molecules adsorbed in restricted spaces. [N. J. Turro, J. K. Barton, D. Tomalia, In Photochem. Convers. Storage Sol. Energy, E. Pelizzetti M. Schiavello Kluwer, Dordrecht, The Netherlands, 1991] [ 469]. 

It was observed in synthetic Linde Type Na-Y, Ba-Y and Zn-Y zeolites (a crystalline aluminosilicate with the formula Nax(A102)x(Si02)y, etc.) that after the NO adsorption, only NO radicals could be detected at 77 K [99]. The use of 15NO gas confirmed the results with uNO. After UV irradiation at 77 K of the NO-treated Ba-Y, only N02 radical spectrum was observed. This photoinduced signal was stable at 77 K, decayed gradually at room temperature (Tj/2 = several hours) and disappeared completely when the sample was annealed at 50° for 30 min [99]. The role of NO, N02 and N2O3 species, photoelectron transfer between them and their reversible transformations have anready been discussed. 

Buhks, A New Theoretical Approach to Photoelectron Transfer Across Semiconductor-Electrolyte Interfaces, in Photoelectro-chemistry Fundamental Processes and Measurement Techniques, W. L. Wallace, A. Nozik, and S. K. Debb, eds., Proc. 

E. Buhks and F. Williams, Proc. Electrochem. Soc. 82 1 (1981). Model for photoelectron transfer from semiconductors. 

Armesto, D., Ortiz, M.J., and Agarrabeitia, A.R. (2004) Novel di-Jt-methane rearrangements promoted by photoelectron transfer and triplet sensitization, in CRC Handbook of Organic Photochemistry and Photobiology, 2nd edn (eds W. M. Horspool and... 

Bauld and coworkers studied the [2+2] cycloaddition of A-vinyl carbazoles 86a and electron-rich styrenes 86b catalyzed by iron(III) catalysts A or B in the presence of 2,2 -bipyridine as a ligand, which was reported originally by Ledwith and coworkers (Fig. 21) [142, 143]. Deuterium-labeling studies provided support for the stepwise nature of the process, consisting of reversible SET oxidation of the electron-rich olefin to a radical cation 86 A. Nucleophilic addition of excess 86 leads to distonic radical cation 86B, which cyclizes to cyclobutane radical cation 86C. Back electron transfer affords cyclobutanes 87 and regenerates the catalyst. Photoelectron transfer catalysis gave essentially the same result, thus supporting the pathway. 

Blasius R, Moucheron C, Kirsch-De Mesmaeker A. Photoadducts of metallic compounds with nucleic acids - role played by the photoelectron transfer process and by the TAP and HAT ligands in the Ru11 complexes. Eur J Inorg Chem 2004 3971-9. 

It is well known that an anion of large molecular size serves as a good nucleophile in polar aprotic solvents and its nucleophilicity decreases with an increase in the protic property of the solvent. Accordingly, polar groups in polymer matrices could affect the photoelectron transfer in viologen molecules. Table 9.2... 

Since the photoreduction of viologen is induced by electron abstraction (oxidation) by the excited bipyridinium cation from the counteranion, it is difficult to relate the photoelectron transfer to the dark redox potential. However, the photosensitivity for the same skeleton is almost proportional to the first dark reduction potential, as mentioned in the previous section. The degree of solvation... 

Since photoelectron transfer of viologens proceeds from counteranions to dications in spite of the large difference of dark redox potentials between both... 

An important peculiarity of these electron photoejections is the dependency of their quantum yield on the nature of the solvent. Large differences may be found between two organic solvents even when the very similar THF and dioxane are compared [84] very efficient electron ejection from tetraphenyleth-ylene dianions in THF and no electron detected in dioxane. The ejection quantum yield rapidly drops when the solvent is no longer water as shown for phenol (H20 0.021 MeOH 0.0018 i-PrOH 0.00045) [85], This reduces the impact of electron ejection on the photoelectron transfers occurring in other solvents than water. 

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