  The electronic properties of metal-molecule interfaces can in principle be
controlled by molecular design and self-assembly, yielding great potential for
future nano- and optoelectronic technologies. However, the coupling between
molecular orbitals and the electronic states of the surface can significantly
influence molecular states. In particular, molecules designed to create
metal-organic self-assembled networks have functional groups that by necessity
are designed to interact strongly with metals. Here, we investigate the
adsorption interactions of a terpyridine (tpy)-based molecule on a noble metal,
Ag(111), by low-temperature scanning tunneling microscopy (STM) and
spectroscopy (STS) together with density functional theory (DFT) calculations.
By comparing the local density of states (DOS) information gained from STS for
the molecule on the bare Ag(111) surface with that of the molecule decoupled
from the underlying metal by a NaCl bilayer, we find that tpy-localized
orbitals hybridize strongly with the metal substrate. Meanwhile, those related
to the phenyl rings that link the two terminal tpy groups are less influenced
by the interaction with the surface. The selective hybridization of the tpy
groups provides an example of strong, orbital-specific electronic coupling
between a functional group and a noble-metal surface, which may alter the
intended balance of interactions and resulting electronic behavior of the
molecule-metal interface.
