title: Orbital redistribution in molecular nanostructures mediated by metal-organic bonds.
abstract: Dicyanovinyl-quinquethiophene (DCV5T-Me2) 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-Me2 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-Me2 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.
authors.affiliation: Institut für Experimentalphysik, Freie Universität Berlin , Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Zechao
authors.initials: Z
authors.lastname: Yang
authors.forename: Martina
authors.initials: M
authors.lastname: Corso
authors.forename: Roberto
authors.initials: R
authors.lastname: Robles
authors.forename: Christian
authors.initials: C
authors.lastname: Lotze
authors.forename: Roland
authors.initials: R
authors.lastname: Fitzner
authors.forename: Elena
authors.initials: E
authors.lastname: Mena-Osteritz
authors.forename: Peter
authors.initials: P
authors.lastname: Bäuerle
authors.forename: Katharina J
authors.initials: KJ
authors.lastname: Franke
authors.forename: Jose I
authors.initials: JI
authors.lastname: Pascual
keywords: atomic force microscopy; metal−organic coordination; molecular orbital alignment; molecular orbital distribution; oligothiophene; scanning tunneling microscopy