Jarvis S P, Taylor S, Baran J D, Champness N R, Larsson J A, Moriarty P
School of Physics &Astronomy, University of Nottingham, Nottingham NG7 2RD, UK.
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
Nat Commun. 2015 Sep 21;6:8338. doi: 10.1038/ncomms9338.
Scanning probe-actuated single molecule manipulation has proven to be an exceptionally powerful tool for the systematic atomic-scale interrogation of molecular adsorbates. To date, however, the extent to which molecular conformation affects the force required to push or pull a single molecule has not been explored. Here we probe the mechanochemical response of two tetra(4-bromophenyl)porphyrin conformers using non-contact atomic force microscopy where we find a large difference between the lateral forces required for manipulation. Remarkably, despite sharing very similar adsorption characteristics, variations in the potential energy surface are capable of prohibiting probe-induced positioning of one conformer, while simultaneously permitting manipulation of the alternative conformational form. Our results are interpreted in the context of dispersion-corrected density functional theory calculations which reveal significant differences in the diffusion barriers for each conformer. These results demonstrate that conformational variation significantly modifies the mechanical response of even simple porpyhrins, potentially affecting many other flexible molecules.
扫描探针驱动的单分子操纵已被证明是一种用于对分子吸附物进行系统原子尺度研究的极其强大的工具。然而，迄今为止，分子构象对推动或拉动单个分子所需力的影响程度尚未得到探索。在这里，我们使用非接触原子力显微镜探测了两种四（4-溴苯基）卟啉构象异构体的机械化学响应，我们发现操纵所需的横向力存在很大差异。值得注意的是，尽管具有非常相似的吸附特性，但势能面的变化能够阻止探针诱导一种构象异构体的定位，同时允许对另一种构象形式进行操纵。我们的结果在色散校正密度泛函理论计算的背景下进行了解释，该计算揭示了每种构象异构体在扩散势垒方面的显著差异。这些结果表明，构象变化显著改变了即使是简单卟啉的机械响应，可能会影响许多其他柔性分子。
