Remarkable effect of bromide ion upon two-dimensional faradaic phase transition of dibenzvl viologen on an HOPG electrode surface : Emergence of two-sten transition
Remarkable effect of bromide ion upon two-dimensional faradaic phase transition of dibenzvl viologen on an HOPG electrode surface : Emergence of two-sten transition
复制标题
溴离子对 HOPG 电极表面二苯并紫精二维法拉第相变的显着影响：双斯坦跃迁的出现
DOI：
10.1016/j.electacta.2013.09.168
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发表时间：
2013
影响因子：
6.6
通讯作者：
Takamasa Sagara
中科院分区：
文献类型：
--
作者：
Tomohiro Higashi;Takamasa Sagara
我们发现，二苄基紫精（dBV）在HOPG电极上经历了两步一级法拉第相变在高浓度的溴离子（Br−）。伏安和电反射测量的结果被用来描述的两步过渡过程的机制。当[Br-] > 180 mM时，在较低的负电位下的过渡步骤归因于dBV二价阳离子（dBV 2+）的气体状吸附层和dBV自由基阳离子（dBVradical dot+）的中间相之间的相变。最有可能的是，中间相是一个二维（2D）有序相，由共吸附的dBVradical dot+和Br−组成，两者都与HOPG表面直接接触。在更负的电势下的过渡步骤归因于dBVradical dot+Br−中间相和dBVradical dot+的2D凝聚相之间的相变。在比中间相更致密的凝聚相中，由于联吡啶鎓自由基阳离子之间的面对面相互作用，dBVradical dot+分子是π堆叠的。该过渡步骤还涉及dBV 2+还原为dBVradical dot+的过程，随后将其并入凝聚相中。在任何浓度的KCl溶液中都没有观察到两步跃迁，在[Br-] < 75 mM的KBr溶液中也没有观察到。其他紫精检查，包括苄基-庚基紫精，没有表现出这样的两步过渡，但单步。仔细分析了过渡的性质，特别是在[Br−]范围从75到180 mM的情况下。
We found that dibenzyl viologen (dBV) on an HOPG electrode undergoes a two-step first order faradaic phase transition at high concentrations of bromide ion (Br−). Results of voltammetric and electroreflectance measurements were used to describe the mechanism of the two-step transition processes. When [Br−] > 180 mM, the transition step at less negative potential was ascribed to a phase transition between a gas-like adsorption layer of dBV dication (dBV2+) and a mesophase of dBV radical cation (dBVradical dot+). Most likely, the mesophase is a two-dimensional (2D) ordered phase composed of co-adsorbed dBVradical dot+and Br−where both are in direct contact with the HOPG surface. The transition step at more negative potential was ascribed to a phase transition between the dBVradical dot+Br−mesophase and a 2D condensed phase of dBVradical dot+. In the condensed phase being denser than the mesophase, dBVradical dot+molecules areπ-stacked due to face-to-face interaction between bipyridinium radical cations. This transition step involves also a reduction process of dBV2+to dBVradical dot+followed by its incorporation into the condensed phase. The two-step transition was not observed in KCl solution of any concentration, either in KBr solution of [Br−] < 75 mM. Other viologens examined, including benzyl–heptyl viologen, did not exhibit such a two-step transition but single-step one. The nature of the transition, especially in the [Br−] range from 75 to 180 mM, was closely analyzed.