Three-step redox in polythiophenes: Evidence from electrochemistry at an ultramicroelectrode
Three-step redox in polythiophenes: Evidence from electrochemistry at an ultramicroelectrode
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DOI：
10.1021/jp9601779
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发表时间：
1996-09-12
影响因子：
--
通讯作者：
Inganas, O
中科院分区：
文献类型：
--
作者：
Chen, XW;Inganas, O
在共轭杂环聚合物中，通常存在不同的氧化程度，被认为是极化子、双极化子和金属状态。利用原位UV-Vis-NIR光谱，我们发现聚(3，4-乙二氧基噻吩基)(PEDOT)也具有这些不同的氧化程度。然而，在循环伏安法(CV)中从未清楚地观察到不同氧化水平之间的转变。相反，它通常显示一个宽氧化峰和两个还原峰。PEDOT在大电极上的循环伏安曲线显示，在低扫描速率下，一对氧化还原峰被0.9V隔开，表明有两个不可逆的电子转移步骤。利用超微电极，我们在PEDOT和聚(3-甲基噻吩基)(PMeT)中发现了这两对氧化还原峰。这两个峰不能用两种形式的物质的存在来解释，无论是由于两种不同的共轭长度，晶相或非晶相，还是由于构象变化而产生的。我们推断应该存在第三个氧化还原峰。快速扫描循环伏安法显示，PEDOT和PMeT在超微电极上均有三个还原峰和两个氧化峰。我们在1，1，1，3，3，3-六氟-2-丙醇(HFA)电解液中发现了三对不能分辨的峰，这三对峰被认为能够稳定自由基阳离子。在超微电极研究中，只有在低温下才能发现三对可逆的氧化还原峰。我们将这三个峰归因于从中性态到极化子，从极化子到双极化子，最后从双极化子到金属态的三个氧化还原步骤，每一步都涉及一个单电子转移。
Different oxidation levels, regarded as polaron, bipolaron, and metallic states, are usually found in conjugated heterocyclic polymers. We found that poly(3,4-ethylenedioxythiophene) (PEDOT) also has these different oxidation levels, using in situ UV-VIS-NIR spectroscopy. The transitions between the different oxidation levels were, however, never clearly observed in cyclic voltammetry (CV). Instead it usually shows a broad oxidation peak and two reduction peaks. The CV of PEDOT at macroelectrodes shows a pair of redox peaks separated by 0.9 V at low scan rates, indicating two irreversible electron transfer steps. Using an ultramicroelectrode, we found these two pairs of redox peaks in PEDOT, as well as for poly(3-methylthiophene) (PMeT). These two peaks cannot be explained by the existence of two forms of the materials, whether due to two different conjugation lengths, crystalline or noncrystalline phases, or created by conformational changes. We deduced that there should be a third redox peak. With fast scan cyclic voltammetry both PEDOT and PMeT on ultramicroelectrodes showed three reduction peaks and two oxidation peaks. We find three ill-resolved pairs of peaks in the CV of PEDOT in 1,1,1,3,3,3-hexafluoro-2-propanol (HFA) electrolytes, which was reported to be able to stabilize radical cations. Only at low temperatures can we find three reversible pairs of redox peaks in the ultramicroelectrode studies. We attribute the three peaks to three redox steps on conversion from the neutral state to polarons, from polarons to bipolarons, and finally from bipolaron to the metallic state, each step involving a one-electron transfer.