Gruhn Nadine E, Macías-Ruvalcaba Norma A, Evans Dennis H
Department of Chemistry, University of Arizona, Tucson, 85721, USA.
J Phys Chem A. 2006 May 4;110(17):5650-5. doi: 10.1021/jp060453b.
The inner reorganization energy of the cation radical of 1,4-bis(dimethylamino)benzene, 1, has been determined to be 0.72 +/- 0.02 eV by means of gas-phase photoelectron spectroscopy (PES). PES studies of 9,10-bis(dimethylamino)anthracene, 2, and 3,6-bis(dimethylamino)durene, 3, demonstrate that their reorganization energies are smaller than that of 1. The effect of lowering the inner reorganization energy on the rate constant for an electrochemical electron-transfer reaction is to increase the electron-transfer rate constant, k(s). However, voltammetric studies of the two-electron oxidation of 2 and 3 indicate that the values of k(s) for each step are smaller than those for 1, in contradistinction to the measured differences in reorganization energies. The voltammetric studies of 2 and 3 were reinterpreted according to a mechanism in which each step of oxidation was written as a two-step process, electron transfer with a small inner reorganization energy plus a chemical step of structural change. The agreement of simulations according to this mechanism with the experimental data was excellent. The new reaction scheme eliminated some suspicious features previously obtained with an analysis where electron transfer and structural change were considered to be concerted. In particular, all electron-transfer coefficients (alpha) were close to one-half, whereas the earlier treatment produced values of alpha much larger or smaller than one-half.
通过气相光电子能谱（PES）测定，1,4-双（二甲氨基）苯阳离子自由基（1）的内重组能为0.72±0.02 eV。对9,10-双（二甲氨基）蒽（2）和3,6-双（二甲氨基）杜烯（3）的PES研究表明，它们的重组能比1的小。降低内重组能对电化学电子转移反应速率常数的影响是增加电子转移速率常数k(s)。然而，对2和3的双电子氧化的伏安研究表明，每一步的k(s)值都比1的小，这与测得的重组能差异相反。根据一种机制对2和3的伏安研究进行了重新解释，在该机制中，氧化的每一步都被写成两步过程，即具有小内重组能的电子转移加上结构变化的化学步骤。根据该机制进行的模拟与实验数据吻合良好。新的反应方案消除了先前分析中一些可疑的特征，在先前分析中，电子转移和结构变化被认为是协同进行的。特别是，所有电子转移系数（α）都接近二分之一，而早期处理得到的α值远大于或小于二分之一。
