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

Abstract

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.