Imine derivatives on Au(111): evidence for "inverted" thermal isomerization.
Imine derivatives on Au(111): evidence for "inverted" thermal isomerization.
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DOI：
10.1021/nn103297e
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发表时间：
2011-02
期刊：
影响因子：
17.1
通讯作者：
J. Mielke;F. Leyssner;M. Koch;S. Meyer;Ying-Zi Luo;S. Selvanathan;R. Haag;P. Tegeder;L. Grill
中科院分区：
文献类型：
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作者：
J. Mielke;F. Leyssner;M. Koch;S. Meyer;Ying-Zi Luo;S. Selvanathan;R. Haag;P. Tegeder;L. Grill
通常在适当波长的光照射下经历反式和顺式状态之间可逆异构化的分子代表了一类重要的分子开关。在这项扫描隧道显微镜 (STM) 和高分辨率电子能量损失光谱 (HREELS) 相结合的研究中，我们报告了 Au(111) 表面上亚胺衍生物的自组装阵列。大多数分子在室温下沉积后处于反式状态，但其中许多分子在加热时改变其构象，我们将其分配为切换到顺式状态。对于许多分子开关，反式异构体是溶液中能量上更稳定的化合物，在充分加热时导致顺式到反式的热弛豫。然而，从表面上看，顺式异构体的数量随着温度的升高而增加，表明存在“反向”热异构化行为。这种表面介导效应的原因可能是与反式状态相比，分子的中心亚胺部分与金表面的耦合更强，这在空间上仅在顺式状态下才有可能。
Molecules that undergo reversible isomerization between trans and cis states, typically upon illumination with light at appropriate wavelengths, represent an important class of molecular switches. In this combined scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS) study, we report on self-assembled arrays of imine derivatives on a Au(111) surface. Most of the molecules are found in the trans state after deposition at room temperature, but many of them change their conformation upon heating, which we assign to switching to the cis state. As for many molecular switches, the trans isomer is the energetically more stable compound in solution, resulting in thermal cis to trans relaxation upon sufficient heating. On the surface, however, the number of cis isomers increases with temperature, pointing toward an "inverted" thermal isomerization behavior. The reason for this surface-mediated effect could be a stronger coupling, as compared to the trans state, of the central imine part of the molecule to the gold surface, which is sterically only possible in the cis state.