Manipulating Localized Molecular Orbitals by Single-Atom Contacts

We have fabricated atom-molecule contacts by attachment of single Cu atoms to terpyridine side groups of bis-terpyridine tetra-phenyl ethylene molecules on a Cu(111) surface. By means of scanning tunneling microscopy, spectroscopy, and density functional calculations, we have found that, due to the localization characteristics of molecular orbitals, the Cu-atom contact modifies the state localized at the terpyridine side group which is in contact with the Cu atom but does not affect the states localized at other parts of the molecule. These results illustrate the contact effects at individual orbitals and offer possibilities to manipulate orbital alignments within molecules.

Figure 1

(a) Molecular structure of BTP-TPE. (b) STM image and STS maps acquired at the indicated bias voltages. The molecular contour of the STM topograph (white line) is overlaid on the STS maps. Image size: $5.0\times 2.5{\mathrm{nm}}^2$. (c) STS spectra acquired at three specific sites marked in the top panel in (b) following the color code. The cyan spectrum was acquired at the Cu surface.

Figure 2

(a) Top and side views of a DFT optimized molecule adsorbed on one layer of Cu atoms. (b) Simulated STM image and PDOS maps at the indicated energies. Image size: $5.0\times 2.5{\mathrm{nm}}^2$. (c) Integrated LPDOSs of the two side groups and the central group. The frontier MOs of a free molecule are shown below the LPDOS.

Figure 3

(a) STM image and STS maps acquired at the indicated bias voltages of a single-side coordinated BTP-TPE. (b) DFT simulated STM image and PDOS maps at the indicated energies. Images in (a) and (b) have the same scale with a size of $5.0\times 2.5{\mathrm{nm}}^2$. (c) Top and side views of a DFT optimized single-side coordinated molecule adsorbed on one layer of Cu atoms. (d) STS spectra acquired at three specific sites as marked in the topmost panel in (c). The cyan spectrum was acquired at the Cu surface. (e) Integrated LPDOSs of the two side groups and the central group.

Figure 4

(a) STM image and STS maps acquired at the indicated bias voltages of a double-side coordinated BTP-TPE. (b) DFT simulated STM image and PDOS maps at the indicated energies. Images in (a) and (b) have the same scale with a size of $5.0\times 2.5{\mathrm{nm}}^2$. (c) Top and side views of a DFT optimized double-side coordinated molecule adsorbed on one layer of Cu atoms. (d) STS spectra acquired at three specific sites as marked in the topmost panel in (c). The cyan spectrum was acquired at the Cu surface. (e) Integrated LPDOSs of the two side groups and the central group. (f) Scheme showing the realignment of the localized MOs by single-atom contacts.