Optical Effects of Divalent Functionalization of Carbon Nanotubes
Optical Effects of Divalent Functionalization of Carbon Nanotubes
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DOI：
10.1021/acs.chemmater.9b01438
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发表时间：
2019-09-10
影响因子：
8.6
通讯作者：
Tretiak, Sergei
中科院分区：
文献类型：
--
作者：
Gifford, Brendan J.;He, Xiaowei;Tretiak, Sergei
单壁碳纳米管（SWCNTs）的共价功能化可以通过产生具有不同局部形态的sp(3)杂化缺陷来调节其光学性质。具有强吸电子能力的基团在实验中导致了红移发射。进一步的红移可以由碳纳米管中与一个以上碳原子结合的基团（“二价功能化”）产生。根据二价功能化的类型，与它们的单价对应物相比，光谱多样性减少了。本文通过低温光谱测量和时间相关密度泛函理论计算，研究了二价功能化对（6,5）swcnts缺陷位点激子定位和发射中相关红移的影响。这些效应的特点是三种二价化合物在官能团中的原子数量和与管的键合模式上不同。发现靠近缺陷位置的两个碳原子的键特性对系统稳定性和光谱红移有显著影响。当SWCNT的杂化保持sp(2)样时，由于其能够与剩余的六边形网络形成平面键，功能化系统是稳定的，而功能化区域的键特性影响红移。这仅对二价物种的某些键的几何形状是可能的，证明了它们的光谱多样性降低。我们进一步表明，在管上空间分离的位置上的功能化可以伴随着第二个化学加合物，并且所产生的缺陷的结构是由第一次加合后的键反应性决定的。这种行为证明了一类具有连接链或高缺陷浓度的二价体系的光谱趋势。这些结果进一步证实，在实验样品中，加合物主要只与swcnts表面邻近的碳（邻位物种）形成化学键。我们对缺陷位点附近的键性质进行了分析，使官能化SWCNTs的单价和二价缺陷态产生的许多光谱特征合理化。这种新兴的认识使得通过仔细控制缺陷结构来调整发射特性成为可能。
Covalent functionalization of single-walled carbon nanotubes (SWCNTs) enables tuning of their optical properties through the generation of sp(3)-hybridized defects with distinct localized morphology. Groups with strong electron-withdrawing abilities result in redshifted emission experimentally. Further redshifts can be generated by groups bound to more than one carbon atom in the SWCNT ("divalent functionalization"). Depending on the type of divalent functionalization, the spectral diversity is reduced compared to their monovalent counterparts. Here we study the effect of divalent functionalization on the exciton localization at the defect site and related redshifts in emission of (6,5) SWCNT through low-temperature spectroscopy measurements and time dependent density functional theory calculations. These effects are characterized for three classes of divalent compounds distinct in the number of atoms in the functional group and bonding pattern to the tube. The bond character of the two carbon atoms proximal to the defect site is found to have a notable impact on the system stability and spectral redshifts. Functionalized systems are stabilized when the hybridization at the SWCNT remains sp(2)-like due to its ability to form planar bonds to the remaining hexagonal network, while bond character in the functionalized regions affects the redshifts. This is only possible for certain bonding geometries in divalent species, justifying their decreased spectral diversity. We further show that functionalization at spatially separated sites on the tube can be accompanied by a second chemical adduct, and the configuration of the resulting defect is dictated by bond reactivity following the first addition. This behavior justifies the spectral trends of a class of divalent systems with linker chains or high defect concentration. These results further corroborate that adducts predominantly form chemical bonds only to the neighboring carbons on the SWCNT surface (ortho species) in experimental samples. Our analysis of bond character in the vicinity of the defect sites rationalizes appearance of many spectral features arising from monovalent and divalent defect states of functionalized SWCNTs. This emerging understanding enables tuning of the emission characteristics through careful control of the defect structure.