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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Effects of counterion mobility, surface morphology, and charge screening on the electron-transfer rates of porphyrin monolayers
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Effects of counterion mobility, surface morphology, and charge screening on the electron-transfer rates of porphyrin monolayers

机译：抗衡离子迁移率，表面形态和电荷筛选对卟啉单层电子传输速率的影响

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The standard electron-transfer rate constants (k(0)) for the oxidation of porphyrin monolayers are reported for a number of solvent/electrolyte systems and electroactive surfaces. The goal is to explain the inverse correlation between the electron-transfer rates and the porphyrin surface concentration (Roth et al., J. Phys. Chem. B 2002, 106, 8639-8648). Each porphyrin is a zinc chelate and contains three meso-mesityl groups and a benzyl alcohol or benzyl thiol for surface attachment. The solvent/electrolyte systems include (i) the organic solvent propylene carbonate containing electrolytes with a common cation and anions of different size/mobility (PF6-, ClO4-, and Cl-) and (ii) neat ionic liquids with a common cation and anions of different size/mobility [(CF3SO2)(2)N- and (NC)(2)N-]. The substrates include Si(100), Au(111), and TiN. The k(0) values observed using electrolytes with PF6-, ClO4-, and (CF3SO2)(2)N- counterions are similar to one another, whereas those observed using electrolytes Cl- and (NC)(2)N- counterions are 2-5 times faster. The faster rates for the latter anions are attributed to their smaller size/higher mobility. The k(0) values observed for monolayers on Si(100) and Au(111) are similar to one another; the k(0) values for monolayers on TiN are similar to 5-fold faster. The faster rates for the TiN substrate are attributed to a rougher surface morphology (as determined via atomic force microscopy measurements) which results in an actual surface concentration that is lower than the concentration based on the geometrical area of a planar substrate. The k(0) values determined for mixed monolayers where the electroactive porphyrin is co-deposited with an electroinactive porphyrin are dependent only on the concentration of the redox-active species, not on the total porphyrin concentration. This behavior is consistent with space-charge effects being the principal determinant of the inverse correlation between the electron-transfer rates and the porphyrin surface concentration. The space charge effects can be mitigated, but not eliminated, by using smaller, more mobile counterions and rougher surfaces.
机译：对于许多溶剂/电解质系统和电活性表面，报告了卟啉单层氧化的标准电子传递速率常数（k（0））。目的是解释电子传递速率与卟啉表面浓度之间的逆相关性（Roth等，J.Phys.Chem.B 2002，106，8639-8648）。每个卟啉是锌螯合物，并包含三个内消旋-间苯二甲酰基和一个用于表面附着的苄醇或苄基硫醇。溶剂/电解质体系包括（i）含有具有共同阳离子和不同尺寸/迁移率的阴离子（PF6-，ClO4-和Cl-）的电解质的有机溶剂碳酸亚丙酯，以及（ii）具有共同阳离子的纯离子液体和大小/迁移率不同的阴离子[（CF3SO2）（2）N-和（NC）（2）N-]。基板包括Si（100），Au（111）和TiN。使用具有PF6-，ClO4-和（CF3SO2）（2）N-平衡离子的电解质观察到的k（0）值彼此相似，而使用电解质Cl-和（NC）（2）N-平衡离子观察到的k（0）值彼此相似。快2-5倍。后一种阴离子的较快速率归因于其较小的尺寸/较高的迁移率。 Si（100）和Au（111）上单层的k（0）值彼此相似; TiN上单层的k（0）值快5倍。 TiN基板的更快速率归因于较粗糙的表面形态（通过原子力显微镜测量确定），这导致实际表面浓度低于基于平面基板几何面积的浓度。对于其中电活性卟啉与电惰性卟啉共沉积的混合单层所确定的k（0）值仅取决于氧化还原活性物质的浓度，而不取决于总卟啉浓度。这种行为与空间电荷效应是一致的，空间电荷效应是电子传输速率与卟啉表面浓度之间反相关的主要决定因素。通过使用更小，更易移动的抗衡离子和更粗糙的表面，可以减轻但不能消除空间电荷效应。

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