  Donor-acceptor (D-A) structured molecules are essential components in organic
electronics. The respective molecular structure of these molecules and their
synthesis are primarily determined by the intended area of application.
Typically, D-A molecules promote charge separation and transport in organic
photovoltaics (OPV) or organic field-effect transistors (OFET). D-A molecules
showing a larger twist angle between D and A units are, e.g., extremely
important for the development of high internal quantum efficiency in organic
light-emitting diodes (OLEDs). A prototypical molecule of this D-A type is
DCzDCN (5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,3-dinitrile). In most
cases, these molecules are only investigated regarding their electronic and
structural interaction in bulk aggregates but not in ultra-thin films supported
by a metallic substrate. Here, we present growth and electronic structure
studies of DCzDCN on a Cu(100) surface. In a complementary approach, through
the use of Scanning Tunneling Microscopy and Spectroscopy (STM and STS), we
were able to view both the adsorption geometry and the local electronic states
of the adsorbed molecules in direct comparison with the integral electronic
structure of the DCzDCN/CU(100) interface using Ultraviolet and Inverse
Photoemission Spectroscopy (UPS and IPS). The orientation of the molecules with
the donor part towards the substrate results in a chiral resolution at the
interface due to the molecular as well as the substrate symmetry and additional
strong molecular electrostatic forces. Thus, the formation of various
bulk-unlike homochiral structures and the appearance of hybrid interface states
(HIS) modifies the molecular electronic properties of the DCzDCN/Cu(100) system
significantly compared to that of a single DCzDCN molecule. This may be not
only useful for optoelectronic applications but also in organic spintronics.
