Linear free-energy relationship for electron-transfer processes of pyrrolidinofullerenes with tetrakis(dimethylamino)ethylene in ground and excited states
作者:Chuping Luo、Mamoru Fujitsuka、Chun-Hui Huang、Osamu Ito
DOI:10.1039/a901837i
日期:——
Systematic studies of electron-transfer processes in the ground states and excited triplet states of pyrrolidinofullerenes C60(C3H6N)R [R=H (1), p-C6H4NO2 (2), p-C6H4CHO (3), p-C6H5 (4), p-C6H4OMe (5), p-C6H4NMe2 (6)]} with tetrakis(dimethylamino)ethylene (TDAE) have been carried out by steady-state and transient absorption measurements in the visible–NIR region. Analyses of the equilibria of the electron-transfer processes in the ground states indicate that free ion radicals are produced in polar solvents. Photoinduced electron-transfer processes viaT(C60(C3H6N)R)* were observed by applying a perturbation to the equilibria of the electron-transfer reactions in the ground states by laser flash photolysis. Based on the relationship of the thermodynamic data and kinetic data, the electron-transfer rate constants in the ground states (ketG) can be evaluated. The ketG values are affected by the substituents to a smaller extent compared with the equilibrium constants (K) in polar solvents; α=0.6 in Δ log ketG=α Δ log K. This α value indicates that the activation energies of forward electron transfer in the ground states vary moderately with the thermodynamic stabilities of (C60(C3H6N)R)-. Electron-transfer rate constants viaT(C60(C3H6N)R)*, which are close to the diffusion-controlled limit, do not show a large substituent effect (α′=0), because of their highly exothermic processes. Such a linear free-energy relationship can be extended to other systems such as T(C60(C3H6N)R)*/N,N-dimethylaniline, from which valuable information for electron-transfer processes can be obtained.
吡咯烷富勒烯基态和激发三重态电子转移过程的系统研究C60(C3H6N)R [R=H (1), p-C6H4NO2 (2), p-C6H4CHO (3), p-C6H5 (4) )、p-C6H4OMe (5)、p-C6H4NMe2 (6)]} 与四(二甲氨基)乙烯 (TDAE) 的结合已通过可见光近红外区域的稳态和瞬态吸收测量进行。对基态电子转移过程平衡的分析表明,极性溶剂中会产生自由基。通过激光闪光光解对基态电子转移反应的平衡施加扰动,观察到通过 T(C60(C3H6N)R)* 的光诱导电子转移过程。根据热力学数据和动力学数据的关系,可以评估基态的电子转移速率常数(ketG)。与极性溶剂中的平衡常数(K)相比,ketG值受取代基的影响较小; α=0.6 in Δ log ketG=α Δ log K。该α值表明基态中正向电子转移的活化能随(C60(C3H6N)R)-的热力学稳定性适度变化。通过 T(C60(C3H6N)R)* 的电子转移速率常数接近扩散控制极限,由于其高放热过程,没有表现出大的取代基效应 (α'=0)。这种线性自由能关系可以扩展到其他体系,例如T(C60(C3H6N)R)*/N,N-二甲基苯胺,从中可以获得电子转移过程的有价值的信息。