Chemical doping of EDOT azomethine derivatives: insight into the oxidative and hydrolytic stability
作者:Andréanne Bolduc、Stéphane Dufresne、W. G. Skene
DOI:10.1039/c2jm14248a
日期:——
A series of EDOT (3,4-ethylenedioxythiophene) containing azomethines were prepared for investigating their opto-electronic properties. These properties were compared to those of their thiophene azomethine counterparts and it was found that incorporating the EDOT moiety resulted in a 30 nm bathochromic shift in the absorbance. Meanwhile, the oxidation potential (Epa) could be reduced by 100 mV by incorporating the electron rich moiety. Cyclic voltammetry revealed a one-electron oxidation process, resulting in a radical cation. This intermediate was stable when the azomethines contained amines in the 2,2′-positions, evidenced by the reversible oxidation in cyclic voltammetry. In contrast, the radical cation was irreversible when the 2,2′-positions were unsubstituted. It was found that the resulting radical cation was coupled by standard anodic polymerisation to form a polymer that was physisorbed onto the ITO electrode. The resulting polymer was mauve in colour with a λmax of 515 nm and a degree of polymerisation of ca. 5. This was spectroscopically determined relative to an EDOT polyazomethine derivative and a soluble thiophene polyazomethine. The stability of the EDOT azomethine derivatives towards electrochemical and chemical oxidation was also spectroscopically investigated. It was found that the resulting radical cation exhibited a ca. 100 nm bathochromic shift in absorbance relative to the neutral form and reversible colour switching between the neutral and oxidized states was possible. Chemical doping with FeCl3 generated a stable dication. High contrast colours between the neutral and oxidized states of the azomethines were observed. Multiple oxidation/neutralisation cycles were possible without detectable colour deterioration, demonstrating the chemical robustness of the conjugated azomethines towards oxidative decomposition and hydrolysis.
研究人员制备了一系列含有 EDOT(3,4-亚乙二氧基噻吩)的偶氮甲烷,以研究它们的光电特性。结果发现,加入 EDOT 分子后,吸光度发生了 30 nm 的浴色偏移。同时,加入富电子分子后,氧化电位(Epa)可降低 100 mV。循环伏安法显示了一个单电子氧化过程,产生了一个自由基阳离子。当偶氮甲基在 2,2′-位含有胺时,这种中间体是稳定的,循环伏安法中的可逆氧化过程证明了这一点。相反,当 2,2′ 位未被取代时,自由基阳离子是不可逆的。研究发现,由此产生的自由基阳离子通过标准阳极聚合作用耦合成聚合物,并被物理吸附在 ITO 电极上。由此产生的聚合物呈淡紫色,λmax 为 515 纳米,聚合度约为 5。此外,还对 EDOT 偶氮亚甲基衍生物在电化学和化学氧化方面的稳定性进行了光谱研究。研究发现,由此产生的自由基阳离子的吸光度相对于中性形式会发生约 100 nm 的浴色偏移,并且可以在中性和氧化态之间进行可逆的颜色切换。通过化学方法掺入 FeCl3 生成了稳定的二阳离子。在偶氮金属的中性态和氧化态之间观察到了高对比度的颜色。在多次氧化/中和循环过程中都不会出现可检测到的颜色劣化现象,这表明共轭偶氮甲基胺对氧化分解和水解具有很强的化学稳定性。