Photoelectron transfer-initiated

On the basis of the Franck-Condon principle, photoelectron transfer between a donor and acceptor molecule proceeds as follows (Fig. 10). Initially, the donor and acceptor are dispersed randomly in a solution. On light absorption, the donor (or acceptor) undergoes a rapid transition to form a Franck-Condon state, which rapidly undergoes nuclear relaxation to an equilibrated state. A further nuclear reorganization takes place before electron transfer. After electron transfer, there is nuclear relaxation to the final, equilibrated product state. 

Cycloaddition with the carbonyl group in nonpolar solvents may involve initial formation of an exciplex, but recent evidence indicates that polar solvents preclude the exciplex to biradical pathway [33]. There are a number of carbo-nyl/alkene pairs that are capable of photoelectron transfer due to their redox potentials (e.g., quinones/tetracyanoethylene (TCNE)). The resultant radical ions can bond to give 1,4-biradicals that close to form oxetanes [34]. 

Photohomolysis reactions of cobalt(III) pseudohalide complexes can be used to effect photoreduction to cobalt(II) complexes. Thus, intramolecular photoelectron transfer in the complexes Co(CN)5N3 and Co(NH3)5N3 leads to oxidation of the azide ion to the azide radical, and reduction of the cobalt(III) center to cobalt(II). Evidence for the initial formation of the azide radical comes from the photolysis of solutions containing Co(CN)5N3 and iodide ion, when the iodine anion radical I2 is observed in the solution. This formation of I2 results from the photochemical generation of the azide radical, which then oxidizes the iodide ion to an iodine atom (Scheme 2.1). Subsequently, spin trapping experiments with phenyl-N-t rf-butyl nitrone has been used to verify the formation of azide radicals from the photolysis of Co(CN)5N and Co(NH3)sN3 / ... 

The Meerwein reaction between phenyl radicals, thermally generated from arenediazonium salts, and alkenes in the presence of copper(l) ions can also be initiated photochemically. Irradiation of the diaz-onium salt in the presence of copper(ll) ions leads to photoelectron transfer and the generation of phenyl radicals. Addition of the radical to an alkene bond becomes a chain reaction mediated by copper ions according to Scheme 5. Quantum yields for the evolution of nitrogen are in the region of 700. ... 

The photoinduced electron transfer (PET) reactivity of phthalimidoacetic acid and the corresponding acetates has been studied in their photodecarboxylation reactions. " A variety of medium- and large-ring compounds are synthesised from co-phthalimidoalkanoates using a triplet sensitized photodecarboxylation reaction initiated by intramolecular photoelectron transfer. " Photodecarboxylation of N-phthaloyP " and N-benzoyl esters of a-amino adds " has also been reported. 

The most probable fate of a photon with an energy higher than the binding energy of an encountered electron is photoelectric absorption, in which the photon transfers its energy to the electron and photon existence ends. As with ionization from any process, secondary radiations initiated by the photoelectron produce additional excitation of orbital electrons. 

The reaction between A-chlorobenzotriazole and l-methyl-2-phenylindole involves formation of the indole radical cation and benzotriazole radical via an initial electron transfer <82JOC4895, 91JCS(P2)1779>. Chemical reactions of benzotriazole on a freshly etched surface of metallic copper are studied by surface-enhanced Raman scattering, x-ray photoelectron spectroscopy, and cyclic voltammetry. The surface product is (benzotriazolato)copper(-l-), which covers the surface in the shape of polymeric material and shows good anticorrosion effects for copper <91JPC7380>. 

The excitation energy produced is sometimes transferred to one of the outer electrons, causing it to be ejected from the atom. This is an Auger electron . The energy of each photoelectron is equal to the difference between the energy of the incident X-ray photon and that of the energy level initially occupied by the ejected... 

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