Au(111)表面一维分子组装中氢键诱导的分子轨道能量位移

Hydrogen bond induced molecular orbital shift in one-dimensional molecular self-assemblies on Au(111)

利用扫描隧道显微术、扫描隧道谱和密度泛函理论研究了茚并[1,2-b]芴-6,12-二酮(IFDO)在Au(111)表面形成的组装结构及其中分子轨道能级的变化.结果表明, IFDO在Au(111)表面通过分子间氢键沿鱼骨重构结构形成一维自组装分子链;位于组装结构中的分子的最低未占轨道相对孤立分子向费米能级方向发生0.16~0.32 e V的位移,且位移大小与分子同周围分子形成氢键的数目和方式有关.通过定量地对比不同氢键环境中分子的轨道能量位移与周围分子极化能大小的变化趋势,发现周围分子的瞬时极性是造成组装结构中IFDO分子轨道能量变化的主要因素.而周围分子的诱导极性则对缺陷结构处分子的轨道能级有不可忽略的影响.实验测得的IFDO分子轨道的能量变化来自于周围分子各向异性的瞬时极性和诱导极性的共同作用.

The self-assembly of indeno[1,2-b]fluorene-6,12-dione(IFDO) absorbed on Au(111) was investigated by scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations. It was found that IFDO molecules assembled into one-dimensional molecular chains along the herringbone structures on the Au(111) surface. The lowest unoccupied molecular orbital of IFDO molecules in the assembled structures, relative to isolated molecules, shifts towards Fermi level. The degree of molecular orbital shift, varying from 0.16 to 0.32 eV,depends on the pattern and number of hydrogen bonds formed between the detected IFDO molecule and its neighboring ones. Both transient and induced polarization of neighboring IFDO molecules contribute to the total polarization energy which leads to molecular orbital shift observed by experiments. The former makes the dominant contribution, while the effect of the latter is appreciable especially for molecules composing the defect structures.