Photo electron transfer intramolecular

The analogous primary amine had been earlier studied by Wubbels and gave only the photo-Smiles reaction, but this process was not observed for the present system and the reaction is suggested to proceed by a photo-electron transfer mechanism to yield the radical ion pair. Photoaddition of N-H bonds to aromatic compounds has been known for some years, and the intramolecular process which leads to cyclization products has been reported for the reaction of 9-(aj-anilinolalkyl)phenanthrenes (220). The formation of the spiro-compounds (221) by addition of the N-H bond across the phenan-threne 9,10-positions is suggested to arise from the intramolecular exciplex in... 

The photo-acid generation and the photosensitivity of three kinds of bis(trichloroethylene)triazine derivatives were reported. From the measurements of absorption, fluorescence and fluorescence quenching spectra and acid generation it was concluded that acid generation has the nature of a photo-electronic transfer process. Results also indicate that the localized excitation and emission is most important for the photo-acid generation and that intramolecular charge transfer effect is important for extension of the absorption... 

Under most conditions several modes of photolysis will compete in a given flavin system (161). If, however, addition and dealkylation do not compete, the most common form of irreversible selfdestruction of flavin, viz. intramolecular dehydrogenation, can be easily suppressed by extraneous photosubstrates, which either induce photo-electron transfer, as for example phenol, which is reversible by itself, or substrate photodehydrogenation, as for example EDTA, which is reversible with oxygen, with respect to Flo (36). In aprotic solvents 1,4-cyclohexadiene performs the same service as EDTA in aqueous environment (97). 

The electron-transfer-induced cyclization of homochrysanthemol proceeds via a flve-membered transition state, from intramolecular substitution at the quaternary cyclopropane carbon, to generate the flve-membered cyclic ethers (69) and (70). In contrast, the intramolecular photo-induced cyclization of chrysanthemol goes via a six-membered transition state involving attack at the terminal vinyl carbon. 

Intramolecular nucleophilic substitution by the anions of o-haloanilides is another viable oxindole synthesis. This is a special example of the category Ic process described in Section 3.06.2.3. The reaction is photo-stimulated and the mechanism is believed to be of the electron-transfer type SRN1 rather than a classical addition-elimination mechanism. The reaction is effective when R = H if 2 equivalents of the base are used to generate the dianion (equation 202) (80JA3646). 

Figure 35 Photo-induced intramolecular electron transfer pathway of complex 80, in the presence of methylviologen (a) The Mn -Ru—MV2+ pathway (b) the Mii - P6S0 --Qa quinone pathway in PSII. (From Ref. 170.)...

FIGURE 23. A scaffold for photo-induced intramolecular energy or electron transfer. 

In conclusion of the discussion concerning intramolecular and intraparticle transmembrane electron transfer, it should be stressed that this sort of PET may occur rather efficiently due to the possibility for this process to attain very high rates. The studies in this direction are still at the beginning. A challenge for chemists here is the synthesis of molecules of the specified structure and length to span the bilayer with appropriate photo- and electrochemical properties and able to be oriented when embedded into the membranes. 

In a supramolecular approach to fullerene-porphyrin hybrids, the assembly of a rigidly connected dyad, in which a zinc tetraphenylporphyrin, Zn(TPP), is noncovalently linked to a C60 derivative via axial pyridine coordination to the metal, was reported [219-222]. Photo excitation of the dyad Zn-complex led to electron transfer with very long lifetimes of the charge-separated pairs, as revealed by optical spectroscopy and confirmed by time-resolved electron paramagnetic resonance spectroscopy. Accordingly, two different solvent-dependent pathways can be considered for the electron-transfer processes. Either the excitation of the porphyrin chromophore is followed by fast intramolecular electron transfer inside the complex, or alternatively the free porphyrin is excited undergoing intermolecular electron transfer when the acceptor molecules ap-... 

Nakadaira, Y., Sekiguchi, A., Funada, Y., and Sakurai, H. (1991) Photo-induced electron transfer reaction of polysilanes, intramolecular trapping of a transient radical cation with a nucleophile. Chemistry Letters, 327-330. 

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 ... 

A spectroscopic investigation of the formation of THF-Cu"Cl2 complexes has been described, and irradiation of [Cu(Dto)2] (Dto = dithiooxalate) has been found to induce an intramolecular Dto Cu two-electron transfer with cleavage of the C-C bond in the Dto ligand and the formation of SCO. The kinetics of photo-oxidation of pyrene by Cu" in SDS micelles have been measured, but oxidants such as Eu" and Hg do not produce pyrene cations. A non-exponential decay of fluorescence is observed, and this is interpreted in terms of a model due to Tachiya which restricts the numbers of quenchers in a micelle. Transient Cu"-alkyl species are formed on flash photolysis of Cu -bis(amino-acid) complexes such as those of serine and valine, and pseudo first order rate constants for the decay of the transients have been obtained. 

That the electron-transfer step occurs predominantly in an intramolecular fashion is probably because of complexation effects in the ground state of the substrates. The synthesis of cyclopeptide model compounds was intensively investigated by use of this photo-decarboxylation route. The yields of these macrocyclizations did not depend on spacer length but on the position of the amide group relative to... 

In the present ehapter we consider the inter- or intramolecular photoinduced electron transfer phenomenon. We mainly focus on photoinduced electron transfer processes that lead to the photoinitiation of polymerization, and on processes initiated by photoredueed or photooxidized excited states. We concentrate especially on a description of the kinetic schemes, a description of the reactions that follow the primary proeess of eleetron transfer, and the characteristics of intermediates formed after electron transfer. Understanding the complexity of the processes of photo-initiated polymerization requires a thorough analysis of the examples illustrating the meehanistie aspects of the formation of free radicals with the ability to start polymerization. 

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