National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, United States.
J Am Chem Soc. 2012 Mar 14;134(10):4850-6. doi: 10.1021/ja211181q. Epub 2012 Feb 28.
The atomic specificity afforded by nuclear magnetic resonance (NMR) spectroscopy could enable detailed mechanistic information about single-walled carbon nanotube (SWCNT) functionalization as well as the noncovalent molecular interactions that dictate ground-state charge transfer and separation by electronic structure and diameter. However, to date, the polydispersity present in as-synthesized SWCNT populations has obscured the dependence of the SWCNT (13)C chemical shift on intrinsic parameters such as diameter and electronic structure, meaning that no information is gleaned for specific SWCNTs with unique chiral indices. In this article, we utilize a combination of (13)C labeling and density gradient ultracentrifugation (DGU) to produce an array of (13)C-labeled SWCNT populations with varying diameter, electronic structure, and chiral angle. We find that the SWCNT isotropic (13)C chemical shift decreases systematically with increasing diameter for semiconducting SWCNTs, in agreement with recent theoretical predictions that have heretofore gone unaddressed. Furthermore, we find that the (13)C chemical shifts for small diameter metallic and semiconducting SWCNTs differ significantly, and that the full-width of the isotropic peak for metallic SWCNTs is much larger than that of semiconducting nanotubes, irrespective of diameter.
核磁共振（NMR）光谱提供的原子特异性，可以使我们详细了解单壁碳纳米管（SWCNT）的功能化机制，以及决定基态电荷转移和分离的非共价分子相互作用，这些作用由电子结构和直径决定。然而，迄今为止，在合成的 SWCNT 群体中存在的多分散性掩盖了 SWCNT（13）C 化学位移对固有参数（如直径和电子结构）的依赖关系，这意味着对于具有独特手性指数的特定 SWCNT，没有获得任何信息。在本文中，我们利用（13）C 标记和密度梯度超速离心（DGU）的组合，产生了一系列具有不同直径、电子结构和手性角的（13）C 标记 SWCNT 群体。我们发现，对于半导体 SWCNT，SWCNT 各向同性（13）C 化学位移随直径的增大而系统地降低，这与最近的理论预测一致，但这些预测迄今为止尚未得到解决。此外，我们发现小直径金属和半导体 SWCNT 的（13）C 化学位移差异显著，并且金属 SWCNT 的各向同性峰的全宽比半导体纳米管大得多，而与直径无关。
