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Excitonic and Vibrational Properties of Single-Walled Semiconducting Carbon Nanotubes

机译：单壁半导体碳纳米管的激子和振动特性

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摘要

We review quantum-chemical studies of the excited-state electronic structure of finite-size semiconducting single-walled carbon nanotubes (SWCNTs) using methodologies previously successfully applied to describe conjugated polymers and other organic molecular materials. The results of our simulations are in quantitative agreement with available spectroscopic data and show intricate details of excited-state properties and photoinduced vibrational dynamics in carbon nanotubes. We analyze in detail the nature of strongly bound first and second excitons in SWCNTs for a number of different tubes, emphasizing emerging size-scaling laws. Characteristic delocalization properties of excited states are identified by the underlying photoinduced changes in charge densities and bond orders. Due to the rigid structure, exciton-phonon coupling is much weaker in SWCNTs compared to typical molecular materials. Yet we find that, in the ground state, a SWCNT's surface experiences the corrugation associated with electron—phonon interactions. Vibrational relaxation following photoexcitation reduces this corrugation, leading to a local distortion of the tube surface, which is similar to the formation of self-trapped excitons in conjugated polymers. The calculated associated Stokes shift increases with enlargement of the tube diameters. Such exciton vibrational phenomena are possible to detect experimentally, allowing for better understanding of photoinduced electronic dynamics in nanotube materials.
机译：我们使用以前成功地用于描述共轭聚合物和其他有机分子材料的方法，回顾了有限尺寸半导体单壁碳纳米管（SWCNT）的激发态电子结构的量子化学研究。我们的模拟结果与可用的光谱数据在数量上一致，并显示了碳纳米管中激发态性质和光致振动动力学的复杂细节。我们详细分析了SWCNT中用于许多不同管子的强约束第一和第二激子的性质，强调了新兴的尺寸缩放定律。激发态的特征离域特性由电荷密度和键序的潜在光诱导变化确定。由于具有刚性结构，与典型的分子材料相比，SWCNT中的激子与声子的耦合要弱得多。然而，我们发现，在基态下，SWCNT的表面会经历与电子-声子相互作用相关的波纹。光激发后的振动松弛减少了波纹，导致管表面局部变形，这类似于在共轭聚合物中形成自陷激子。计算的相关斯托克斯位移随管直径的增大而增加。这种激子振动现象可以通过实验检测，从而可以更好地理解纳米管材料中的光诱导电子动力学。

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