Self-sensitized photo-oxidation

Krieg, M. and Whitten, D.G. (1984a) Self-sensitized photo-oxidation of protoporphyrin IX and related porphyrins in erythrocyte ghosts and microemulsions a novel photooxidation pathway involving singlet oxygen, J. Photochem., 25 235-252. 

HAS are weaker quenchers of 02 than aromatic amines [208]. Extensive quenching studies were performed with aliphatic and heterocyclic amines [209]. Data obtained in the inhibition of the self-sensitized photo-oxidation of rubrene revealed that the quenching efficiency of unhindered amines may be correlated with their ionization potentials. A low ionization potential means a better quenching activity. Substitution on the a-carbon atom to nitrogen by alkyls reduces the quenching rate predicted from the ionization potential [208, 209]. The sensitivity of 02 quenching to steric effects may be exemplified with quenching rate constants kq(in dm3 mol was used as a standard. 

Rubrene also reacts with oxygen and forms rubrene endoperoxide in the process of self-sensitized photo-oxidation [98,105]. Oxidation of rubrene is restricted to a thin surface layer [106], The role of the surface endoperoxide in the charge transport properties of rubrene OFETs is still unclear and more work is needed in this direction. For example, surface endoperoxide might help to protect the conduction channel... 

The role of exciplexes in self-sensitized photo-oxidations has been further investigated by Stevens and co-workers.273 - Photoperoxidation of 1,3-diphenyl-isobenzofuran in solution proceeds at a rate which is independent of acceptor concentration when this is very low, and this observation has been interpreted in terms of a re-encounter of x02 and ground-state acceptor molecules generated in the same triplet-triplet annihilation act. This interpretation accounts for the failure of tetramethylethylene to inhibit the reaction completely. Processes 1—3 in Scheme 8 account for the observations if re-encounter effects are included,... 

Schmidt, R. and Brauer, H. D., Self-sensitized photo-oxidation of aromatic compounds and photocycloreversion of endoperoxides. Application in chemical actinometry, /. Photochem., 25, 489, 1984. 

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