模板导向π共轭卟啉纳米管的反常带隙振荡
Unusual Bandgap Oscillations in Template-Directed π-Conjugated Porphyrin Nanotubes
摘要：
使用大规模DFT计算（高达1，476个原子和18，432个轨道），我们首次详细分析了最近合成的卟啉纳米管的不寻常的电子性质。我们令人惊讶地观察到这些纳米结构的带隙中作为尺寸的函数的极大振荡，这与典型的量子限制效应（即，在这些纳米管中的几个中，带隙随着尺寸而增加）。特别是，我们发现，这些有趣的电子振荡产生的芳香族/非芳香族特性在这些卟啉纳米管的大小依赖性的交替。我们的能带结构和轨道图的分析表明，在这些纳米结构的电子跃迁是直接带隙，光学活性的“亮”状态，可以很容易地观察到在光电子能谱实验。最重要的是，由于它们不寻常的带隙振荡，我们发现，I型和II型供体-受体p-n异质结是可能的，在这些模板导向的，“自下而上合成”卟啉纳米管-一个独特的属性，是不存在于传统的碳纳米管。
英文摘要：
Using large-scale DFT calculations (up to 1,476 atoms and 18,432 orbitals), we present the first detailed analysis on the unusual electronic properties of recently synthesized porphyrin nanotubes. We surprisingly observe extremely large oscillations in the bandgap of these nanostructures as a function of size, in contradiction to typical quantum confinement effects (i.e., the bandgap increases with size in several of these nanotubes). In particular, we find that these intriguing electronic oscillations arise from a size-dependent alternation of aromatic/non-aromatic characteristics in these porphyrin nanotubes. Our analyses of band structures and orbital diagrams indicate that the electronic transitions in these nanostructures are direct-bandgap, optically active "bright" states that can be readily observed in photoelectron spectroscopic experiments. Most importantly due to their unusual bandgap oscillations, we find that both type I and type II donor-acceptor p-n heterojunctions are possible in these template-directed, "bottom-up synthesized" porphyrin nanotubes - a unique property that is not present in conventional carbon nanotubes.
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