BELL-SHAPED ENERGY-GAP DEPENDENCE OF BACKWARD ELECTRON-TRANSFER OCCURRING WITHIN GEMINATE RADICAL PAIRS PRODUCED BY QUENCHING OF RUTHENIUM(II) POLYPYRIDINE COMPLEXES BY AROMATIC-AMINES

被引:79
作者
OHNO, T [1 ]
YOSHIMURA, A [1 ]
MATAGA, N [1 ]
机构
[1] OSAKA UNIV,FAC ENGN SCI,DEPT CHEM,TOYONAKA,OSAKA 560,JAPAN
关键词
D O I
10.1021/j100375a023
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
Laser flash spectroscopy has demonstrated that the bimolecular quenching of MLCT excited triplet states of RuL32+ (L = 2,2-bipyridine (bpy), 1,10-phenanthroline (phen), and 4,7-diphenyl-1,10-phenanthroline (dp-phen)) produces Ru(L•-)L2+ and a cation radical of the quencher (aromatic amine) in a mixed solvent of acetonitrile and water (1:1 by volume). Quantum yields of Ru(L•-)L2+ production in the bulk were spectroscopically determined by using the molar absorption coefficients of Ru(L•-)L2+ and 3RuL32+, which were obtained by use of energy transfer from 3Ru(phen)32+ and 3Ru(dp-phen)32+ to anthracene. Rate constants (kb) of the backward electron transfers that occur within the geminate radical pair formed in the quenching were estimated from the quantum yields of Ru(L•-)L2+. A decrease in kb of highly exergonic electron transfer with an increase in the exergonicity (-ΔG°) was observed, with the maximum in kb at ΔG° = -1.7 eV for the three compounds. The ΔG° dependence of kb is discussed in terms of nuclear rearrangement and nuclear tunneling. © 1990 American Chemical Society.
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页码:4871 / 4876
页数:6
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