手性单壁碳纳米管旋光异构体的主-客体化学识别分离法

Chiral single-walled carbon nanotubes (SWNTs) have two enantiomers which are mirror images each other. It is crucial to achieve the two enantiomers of chiral SWNTs for the study and understanding of the fundamental optical properties of one dimensional closed system, as well as for the developing of new electronic and spintronic materials to be able to control the photon absorption and emission as never before. However, current methods of synthesizing SWNTs result inevitably in racemic mixtures of right- and left-handed SWNTs with a specific chirality, which have impeded the study of the enantiomers of SWNTs. In this project, arc-discharged SWNTs are dispersed in water or organic solvent by the host-guest chemical recognition of some novel separating reagents with the assistance of sonication. The affinity of the right-handed carbon nanotubes with a specific separating reagent is expected to be different from that of the left-handed counterpart, which would lead to their differences both in solubility and in buoyant density. Thus, it is quite possible to achieve effecient sorting of the right-handed and/or left-handed enantiomers of a specific chiral SWNTs by a nonlinear density gradient ultracentrifugation. One dimensional nano optically active crystal would be self-assembled by some crystal growth technologies, from the dispersion of the right- or left-handed SWNTs, with the guidance of some separating reagents around individual nanotubes. The scientific question, whether the nano optical active crystals are composed of SWNTs with the same chirality and the same handedness, will be clarified by structural characterization. Some novel properties of the one-dimensional nano optical active crystals might be discovered by the detailed study of their electrical, optical and magnetic anisotropy properties, which might lead to their application as novel optoelectronic materials.

手性单壁碳纳米管有两个互为镜像的旋光异构体。无论是对研究和理解一维封闭体系的基础光学性质，还是对开发能够控制光子的吸收和发射的全新的光电子和自旋电子材料，获得碳纳米管的旋光异构体都是至关重要的。本课题拟通过新型分离试剂对手性单壁碳纳米管的主-客体化学识别作用，在超声波辅助下将电弧放电法合成的碳纳米管单分散在水或者有机溶剂中；利用单壁碳纳米管的左旋和右旋异构体与分离试剂螺旋状组装体之间因亲合力的不同所产生的溶解性和浮力密度的差异，经过密度梯度超速离心处理达到不同手性单壁碳纳米管旋光异构体的有效分离；采用晶体生长技术，在分离试剂分子的导引作用下自组装碳纳米管旋光晶体，通过结构表征阐明它们是否是由相同手性和相同螺旋方向的碳纳米管构成的科学问题，从而建立一种分离和提纯碳纳米管旋光异构体的新方法。通过电、光和磁学等性能的测试发现该一维纳米晶体的某些新颖的性质，并探索将它们用做新型光电子材料的可能。

电弧放电法所合成的单壁碳纳米管（SWNTs）缺陷少、长度长、管壁直，聚集成粗大的管束，因此对它们的分散和分离更加困难。本项目通过电弧放电大量制备了SWNTs，利用它们与四大类新型手性分散试剂所形成的主-客体化学识别作用，经由非线性密度梯度来分离具有单一导电性或者旋光活性的SWNTs。. 不同侧链接枝的聚甲基硅烷对大直径和小螺旋角的金属性SWNTs具有很高的选择性分散作用，侧链越长选择性越高，这是聚甲基硅烷到SWNTs的电荷转移的结果。电化学研究表明聚甲基(1-十一羧酸基)硅烷所分散的碳纳米管具有优异的电化学活性。. 三苯胺聚酰亚胺类高聚物对半导体性SWNTs的选择性分散作用是随着主链和侧链长度的增加而增强的。主链与SWNTs以π-π相互作用相结合的，主链越长这种相互作用越强；而侧链起到了调节主链在SWNTs表面取向的作用，并且侧链越长这种调节作用越明显。. 合成八种天然α氨基酸的十二烷酰基衍生物，它们对SWNTs都有分散作用，尤以十二酰基亮氨酸钠效果最优，这是共轭的氨基酸头基与SWNTs之间的π-π相互作用的结果。从氨基酸衍生物到纳米管的电荷转移致使前者对半导体性SWNTs具有一定的选择性。. 烷基（乙基，正丁基，正己基和正辛基）化的3-甲基咪唑氟硼酸盐离子液体对SWNTs有选择性分散作用，其中正己基化的咪唑基离子液体的分散能力最强。乙基与正丁基长度短，它们与SWNTs的CH-π相互作用弱；正辛基化的咪唑基离子液体的水溶性差。烷基（正丁基，正十二烷基和正十六烷基）化的吡啶氟硼酸盐离子液体对SWNTs的选择性分散作用是随着烷基链的增大而增大的，这是它们与SWNTs之间的CH-π相互作用增大的结果。. 通过非线性密度梯度分离法获得了高纯度的半导性SWNTs和较高纯度的金属性SWNTs。采用慢蒸发溶剂的方法，从单根分散的SWNTs生长出长程有序排列、长而直的纳米晶体。