Electronic to vibrational energy conversion and charge transfer contributions during quenching by molecular oxygen of electronically excited triplet states

被引:43
作者
Abdel-Shafi, AA [1 ]
Wilkinson, F
机构
[1] Ain Shams Univ, Fac Sci, Dept Chem, Cairo 11566, Egypt
[2] Univ Loughborough, Dept Chem, Loughborough LE11 3TU, Leics, England
关键词
D O I
10.1039/b108272h
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The bimolecular rate constants k(q)(T) for quenching of some substituted naphthalene triplet states by molecular oxygen (O-2(3Sigma(g)(-))) in acetonitrile and cyclohexane and the efficiencies, f(Delta)(T), with which singlet oxygen (O-2*((1)Delta(g))) is thereby produced are reported for naphthalene derivatives with wider range of oxidation potentials than those previously measured. The magnitude of k(q)(T) and f(Delta)(T) are inversely correlated, and both parameters exhibit pronounced sensitivity to the oxidation potential (E-M(OX)) of the naphthalene derivative and to the solvent polarity. The modified charge transfer mediated mechanism of quenching based on singlet and triplet channels for oxygen quenching is invoked to discuss these results. In cyclohexane the maximum value for f(Delta)(T) of one is observed for compounds with high oxidation potentials indicating no contribution from the triplet channel whilst in acetonitrile the limit for f(Delta)(T) of 0.25 expected when singlet and triplet channels give equal contributions, when spin statistics is taken into account, is observed for 2,6-dimethoxynaphthalene, which is the derivative with the lowest oxidation potential. These results are combined with those previously reported by ourselves in cyclohexane in order to examine the dependence of the quenching rate constants due to energy transfer on the energy gap (E-T-E-1Sigma). This allows the quenching rate constants due to energy transfer in cyclohexane to be separated into contributions with and without charge transfer assistance. The latter contribution shows smooth dependence on (E-T-E-1Sigma) and the same dependence on the electronic energy, which has to be converted into vibrational energy, probably applies when the solvent is acetonitrile since making this assumption results in similar dependences of the charge transfer contributions in both singlet and triplet channels in acetonitrile. The free energy of activation for charge transfer assisted quenching is shown to have linear dependence on the free energy change for full charge transfer but the indications are that quenching is via singlet and triplet charge transfer complexes with only partial charge transfer character being 12.5% and 17% in acetonitrile and cyclohexane respectively.
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页码:248 / 254
页数:7
相关论文
共 38 条
[1]   Photosensitized generation of singlet oxygen from vinyl linked benzo-crown-ether-bipyridyl ruthenium(II) complexes [J].
Abdel-Shafi, AA ;
Beer, PD ;
Mortimer, RJ ;
Wilkinson, F .
JOURNAL OF PHYSICAL CHEMISTRY A, 2000, 104 (02) :192-202
[2]   Charge transfer effects on the efficiency of singlet oxygen production following oxygen quenching of excited singlet and triplet states of aromatic hydrocarbons in acetonitrile [J].
Abdel-Shafi, AA ;
Wilkinson, F .
JOURNAL OF PHYSICAL CHEMISTRY A, 2000, 104 (24) :5747-5757
[3]   Singlet oxygen formation efficiencies following quenching of excited singlet and triplet states of aromatic hydrocarbons by molecular oxygen [J].
Abdel-Shafi, AA ;
Worrall, DR ;
Wilkinson, F .
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 2001, 142 (2-3) :133-143
[4]   Photosensitized generation of singlet oxygen from ruthenium(II)-substituted benzoaza-crown-bipyridine complexes [J].
Abdel-Shafi, AA ;
Beer, PD ;
Mortimer, RJ ;
Wilkinson, F .
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 2000, 2 (14) :3137-3144
[5]   TRIPLET-STATE ENERGY-DEPENDENCE OF THE COMPETITIVE FORMATION OF O2(1-SIGMA-G+), O2(1-DELTA-G) AND O2(3-SIGMA-G-) IN THE SENSITIZATION OF O2 BY TRIPLET-STATES [J].
BODESHEIM, M ;
SCHUTZ, M ;
SCHMIDT, R .
CHEMICAL PHYSICS LETTERS, 1994, 221 (1-2) :7-14
[6]  
Bu''nau G. v., 1970, RANG DALESPHARMACOLO, V74, P1294, DOI [10.1002/bbpc.19700741223, DOI 10.1002/BBPC.19700741223]
[7]   Charge transfer interactions in the generation of singlet oxygen O2(1Δg) by strong electron donors [J].
Darmanyan, AP ;
Lee, W ;
Jenks, WS .
JOURNAL OF PHYSICAL CHEMISTRY A, 1999, 103 (15) :2705-2711
[8]   QUENCHING OF TRIPLET-STATES BY MOLECULAR-OXYGEN AND ROLE OF CHARGE-TRANSFER INTERACTIONS [J].
GARNER, A ;
WILKINSON, F .
CHEMICAL PHYSICS LETTERS, 1977, 45 (03) :432-435
[9]  
GIJZEMAN OL, 1973, J CHEM SOC FARAD T 2, V69, P708, DOI 10.1039/f29736900708
[10]   MECHANISM OF THE TRIPLET-STATE QUENCHING BY MOLECULAR-OXYGEN IN SOLUTION [J].
GREWER, C ;
BRAUER, HD .
JOURNAL OF PHYSICAL CHEMISTRY, 1994, 98 (16) :4230-4235