Department of Chemistry, French Family Science Center, Duke University , Durham, North Carolina 27708, United States.
J Am Chem Soc. 2013 Oct 30;135(43):16220-34. doi: 10.1021/ja408430v. Epub 2013 Oct 21.
We establish the requisite design for aryleneethynylene polymers that give rise to single-handed helical wrapping of single-walled carbon nanotubes (SWNTs). Highly charged semiconducting polymers that utilize either an (R)- or (S)-1,1'-bi-2-naphthol component in their respective conjugated backbones manifest HRTEM and AFM images of single-chain-wrapped SWNTs that reveal significant preferences for the anticipated helical wrapping handedness; statistical analysis of these images, however, indicates that ∼20% of the helical structures are formed with the "unexpected" handedness. CD spectroscopic data, coupled with TDDFT-based computational studies that correlate the spectral signatures of semiconducting polymer-wrapped SWNT assemblies with the structural properties of the chiral 1,1'-binaphthyl unit, suggest strongly that two distinct binaphthalene SWNT binding modes, cisoid-facial and cisoid-side, are possible for these polymers, with the latter mode responsible for inversion of helical chirality and the population of polymer-SWNT superstructures that feature the unexpected polymer helical wrapping chirality at the nanotube surface. Analogous aryleneethynylene polymers were synthesized that feature a 2,2'-(1,3-benzyloxy)-bridged (b)-1,1'-bi-2-naphthol unit: this 1,1'-bi-2-naphthol derivative is characterized by a bridging 2,2'-1,3 benzyloxy tether that restricts the torsional angle between the two naphthalene subunits along its C1-C1' chirality axis to larger, oblique angles that facilitate more extensive van der Waals contact of the naphthyl subunits with the nanotube. Similar microscopic, spectroscopic, and computational studies determine that chiral polymers based on conformationally restricted transoid binaphthyl units direct preferential facial binding of the polymer with the SWNT and thereby guarantee helically wrapped polymer-nanotube superstructures of fixed helical chirality. Molecular dynamics simulations provide an integrated picture tying together the global helical superstructure and conformational properties of the binaphthyl units: a robust, persistent helical handedness is preferred for the conformationally restricted transoid binaphthalene polymer. Further examples of similar semiconducting polymer-SWNT superstructures are reported that demonstrate that the combination of single-handed helical wrapping and electronic structural modification of the conjugated polymer motif opens up new opportunities for engineering the electro-optic functionality of nanoscale objects.
我们设计了一种芳基乙炔聚合物，这种聚合物可以使单壁碳纳米管（SWNTs）单向螺旋缠绕。在各自的共轭主链中使用（R）-或（S）-1,1'-联-2-萘酚组分的高电荷半导体聚合物，在 HRTEM 和 AFM 图像中显示出单链缠绕的 SWNTs，这些图像显示出对预期螺旋缠绕手性的显著偏好；然而，这些图像的统计分析表明，约 20%的螺旋结构具有“意外”的手性。CD 光谱数据，以及基于 TDDFT 的计算研究，将半导体聚合物包裹的 SWNT 组装体的光谱特征与手性 1,1'-联萘单元的结构特性相关联，强烈表明这些聚合物可能存在两种不同的联萘 SWNT 结合模式，顺式-面对和顺式-侧，后者模式负责螺旋手性的反转和聚合物-SWNT 超结构的形成，这些超结构在纳米管表面具有意外的聚合物螺旋缠绕手性。合成了类似的芳基乙炔聚合物，其特征在于具有 2,2'-(1,3-苯氧基)-桥接（b）-1,1'-联-2-萘酚单元：这种 1,1'-联-2-萘酚衍生物的特征在于其桥接的 2,2'-1,3 苯氧基键，该键限制了两个萘基亚基沿着其 C1-C1'手性轴的扭转角，使其达到更大的、倾斜的角度，从而促进了萘基亚基与纳米管的更广泛的范德华接触。类似的微观、光谱和计算研究确定，基于构象受限的反式联萘基单元的手性聚合物优先定向聚合物与 SWNT 的面结合，从而保证具有固定螺旋手性的螺旋包裹聚合物-纳米管超结构。分子动力学模拟提供了一个整体图像，将全局螺旋超结构和联萘基单元的构象性质联系在一起：对于构象受限的反式联二萘基聚合物，优选稳定、持久的螺旋手性。报告了更多类似的半导体聚合物-SWNT 超结构的例子，这些例子表明，单一螺旋缠绕和共轭聚合物基元的电子结构修饰的结合为纳米尺度物体的光电功能工程开辟了新的机会。
