Journal
ACS NANO
Volume 8, Issue 10, Pages 10715-10722Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn504431e
Keywords
oligothiophene; scanning tunneling microscopy; atomic force microscopy; metal-organic coordination; molecular orbital alignment; molecular orbital distribution
Categories
Funding
- Chinese CSC program
- Alexander von Humboldt Foundation
- DFG [Sfb 658, FR2726/1]
- Freie Universitat Berlin
- Spanish MINECO [MAT2012-38318-C03-02, MAT2013-46593-C6-01]
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Dicyanovinyl-quinquethiophene (DCV5T-Me-2) is a prototype conjugated oligomer for highly efficient organic solar cells. This class of oligothiophenes are built up by an electron-rich donor (D) backbone and terminal electron-deficient acceptor (A) moieties. Here, we investigated its structural and electronic properties when it is adsorbed on a Au(111) surface using low temperature scanning tunneling microscopy/spectroscopy (STM/STS) and atomic force microscopy (AFM). We find that DCV5T-Me-2 self-assembles in extended chains, stabilized by intercalated Au atoms. The effect of metal-ligand hybridization with Au adatoms causes an energetic downshift of the DCV5T-Me-2 lowest unoccupied molecular orbital (LUMO) with respect to the uncoordinated molecules on the surface. The asymmetric coordination of a gold atom to only one molecular end group leads to an asymmetric localization of the LUMO and LUMO+1 states at opposite sides. Using model density functional theory (DFT) calculations, we explain such orbital reshaping as a consequence of linear combinations of the original LUMO and LUMO+1 orbitals, mixed by the attachment of a bridging Au adatom. Our study shows that the alignment of molecular orbitals and their distribution within individual molecules can be modified by contacting them to metal atoms in specific sites.
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