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Sensitization of O2(1Δg) by N-methylacridone. Solvent and O2-concentration dependence and 16O/18O isotope exchange experiments

✍ Scribed by J. Bendig; R. Schmidt; H.-D. Brauer

Publisher
Elsevier Science
Year
1993
Tongue
English
Weight
562 KB
Volume
202
Category
Article
ISSN
0009-2614

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✦ Synopsis

The quantum yield of singlet oxygen O,( '4) formation by the ketone N-methylacridone (NMA) varies strongly with solvent: 0.05 (methanol) Q QsMA 6 0.29 (tetrachloromethane). The analysis of the solvent and O+oncentrationdependent data on NMA fluorescence demonstrates that O,(tAJ is only formed in quenching of the ketone's triplet state by O2 with an efficiency of S&=0.29 being independent of solvent polarity. Thus the solvent effect on the quantum yield of intersystem crossing determines the solvent dependence of Q g" The small value of S, could lead to the expectation that the T, state of NMA is an nx* state.

However, NMA definitely has a T,(nx*) state. Therefore a strict classification of values of S, corresponding to T, (nn*) ketones (S,zO.3) and Tt(nr*) ketones (0.7 sS*b 1) does not exist. Results of photochemical t60/'r0 isotope exchange experiments exclude the participation of a trioxetane in the diabatic deactivation route to the ground state ketone and O,(%c,j.

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