ISSN:
0021-8383
Schlagwort(e):
Chemistry
;
Organic Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Photoexcited zink tetraphenylporphyrin (ZnTPP) reacts with arene diazonium salts via electron transfer according to the oxidation mechanism. This is proved by ESR spectroscopy of ZnTPP+ formed and the fact that N2 and ZnTPP+ are formed in a molar ratio.Due to very different life-times of1(ZnTPP)* and 3(ZnTPP)* it is possible to differentiate between singlet and triplet electron transfer reactions using different diazonium salt concentrations. In this way, the respective quenching constants are determined by means of flash spectroscopy.Due to electron back transfer the singlet reaction at high concentrations of diazonium salts (0.1M) is inefficient (quantum yield 0.1), whereas back electron transfer is symmetry-forbidden in the triplet reaction which, therefore, proceeds with high quantum yields, mearly reaching the ISC quantum yield.From differences between the triplet quenching constants determined by flash spectroscopy and from product quantum yields, respectively, and from corresponding kinetic models it is concluded that the triplet reaction proceeds via a reversibly formed triplet exciplex.Complexes of meso tetraphenyl porphyrin containing Pb(II), Sn(IV), Mn(II), Ni(II), Cu(II) and Fe(III), respectively, have lower sensitization activities decreasing in the order, given in the text.
Zusätzliches Material:
5 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/prac.19853270105
