ELECTRIC PROPERTY OF INSULATED MOLECULAR WIRE FORMED BY CONJUGATED CONDUCTING POLYMERS

我们最近发现了一种由聚合物和环糊精（CD）导电形成的新型分子线。将CD分子与典型的可溶性导电聚合物聚苯胺（PANI）结合，形成项链状包合物。这种包合物可以看作是绝缘的分子线，因为导电聚合物被CD分子作为绝缘体覆盖。在本研究中，我们用CDs和导电聚合物聚苯胺合成了分子纳米管的绝缘分子线，并用原子力显微镜（AFM）观察了绝缘分子线的结构。结果表明，在非接触模式下，原子力显微镜可以清晰地观察到绝缘分子线的棒状结构。室温下，CD与聚苯胺之间的包合作用较弱，无法形成包合物。而分子纳米管可以在室温下形成绝缘的分子线。这些结果表明，分子纳米管与聚苯胺的包合作用比cd强得多。此外，我们发现绝缘分子线在接触模式下与AFM尖端移动或切割。这些结果表明，原子力显微镜可以对绝缘分子线进行操纵。该技术适用于用绝缘分子线连接任意两点。最后，我们对绝缘分子线进行了掺杂。众所周知，未掺杂的导电聚合物具有较低的导电性，并且随着掺杂和半导体的加入，其导电性急剧提高。吸收光谱和原子力显微镜观察结果表明，HCl可以掺杂绝缘分子线。期望掺杂的绝缘分子线具有较高的导电性。研究结果表明，导电聚合物和分子纳米管的绝缘分子线是一种很有前途的新型分子线候选材料，引起了许多研究者的兴趣。

We have recently found a novel kind of molecular wire formed by conducting polymer and cyclodextrin (CD) with cyclic form. CD molecules were threaded onto a typical soluble conducting polymer, polyaniline (PANI), in solution and formed a necklace-like inclusion complex. This inclusion complex can be regarded as insulated molecular wire, because a conducting polymer is covered by CD molecules as insulator.In this study, we formed the insulated molecular wire of the molecular nanotube synthesized from CDs and a conducting polymer, PANI, and observed the structure of the insulated molecular wire by atomic force microscopy (AFM). As a result, we observed rod-like forms of the insulated molecular wires clearly by AFM in non-contact mode. The inclusion interaction between CD and PANI was too weak to form the inclusion complex at room temperature. In contrast, the molecular nanotube can form the insulated molecular wire at room temperature. These results suggest that the molecular nanotube has much stronger inclusion interaction with PANI than CD.Further, we found that the insulated molecular wire was moved or cut with the AFM tip in the contact mode. These results indicate that the insulated molecular wire can be manipulated by AFM.This technique is applicable for the connection between any two points with the insulated molecular wire.Finally, we doped the insulated molecular wire. It is well known that undoped conducting polymer shows low conductivity and the conductivity increases drastically with doping as well as semiconductors. The results of the absorption spectrum and the AFM observation indicated that the insulated molecular wire could be doped by addition of HCl. It is expected that the doped insulated molecular wire has high conductivity.The results in this study indicate that the insulated molecular wire of conducting polymers and molecular nanotubes is a promising candidate novel material for molecular wire, which has attracted interests of many researchers.