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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electron Transfer on Insulator Surfaces: Exciplex Emission and the Role of Electron Diffusion in Determining Radical Deactivation Rates
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Electron Transfer on Insulator Surfaces: Exciplex Emission and the Role of Electron Diffusion in Determining Radical Deactivation Rates

机译：绝缘体表面上的电子转移：激态发射和电子扩散在确定自由基失活速率中的作用

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摘要

The kinetics of electron transfer on silica gel between the anthracene radical cation and the electron donors triphenylamine (TPA) and N, N, N', N'-tetramethyl-1, 4-phenylenediamine (TMPD) have been investigated using the technique of diffuse reflectance laser flash photolysis. The mean rate of decay of the anthrancene radical cation, determined as the maximum of the rate constant distribution, correlates with the surface concentration of the electron donor in both cases up to a loading of 2 μmol g~(-1). In the case of triphenylamine as donor, using 355 nm excitation, plots of mean electron-transfer rate constant versus electron-donor concentration deviate positively from linearity at higher donor concentrations. In the case of TMPD, linearity is preserved at higher loadings with 355 nm excitation, where TMPD does not absorb appreciably and is not therefore directly photoionized, but again a positive deviation ensues with 266 nm excitation that causes direct photoionization of TMPD. In both cases the increased rate of decay of the anthracene radical cation correlates with appreciable direct photoionization of the electron donor. The enhanced rate of decay is explained as being due to donor photoionization increasing the local concentration of electrons on the surface and electron diffusion competing efficiently with donor diffusion leading to increased anthrancene radical cation decay. In addition, we have demonstrated the formation between anthrancene and TPA coadsorbed on silica gel of an emissive exciplex and have found no evidence that relaxation of this exciplex results in radical ion pair formation.
机译：使用扩散技术研究了蒽自由基阳离子与电子给体三苯胺（TPA）和N，N，N'，N'-四甲基-1，4-苯二胺（TMPD）之间在硅胶上电子转移的动力学反射率激光闪光光解。在两种情况下，直至负载量为2μmolg〜（-1）时，蒽基自由基阳离子的平均衰变速率均被确定为速率常数分布的最大值，与电子供体的表面浓度相关。在三苯胺作为供体的情况下，使用355 nm激发，在较高供体浓度下，平均电子传输速率常数与电子供体浓度的关系曲线与线性呈正偏差。在TMPD的情况下，在355 nm激发下较高的负载下可保持线性，其中TMPD不会明显吸收，因此不会被直接电离，但在266 nm激发下仍会出现正偏差，从而导致TMPD直接光电离。在这两种情况下，蒽自由基阳离子的衰变速率增加都与电子给体的明显直接光电离有关。衰变速率的增加被解释为是由于施主光电离作用增加了表面上电子的局部浓度，并且电子扩散与施主扩散有效竞争，从而导致蒽基自由基阳离子的衰变增加。另外，我们已经证明了在蒽醌和TPA之间共吸附在发射激基复合物的硅胶上的形成，并且没有发现该激基复合物的弛豫导致自由基离子对形成的证据。

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