  N-Heteropolycyclic aromatic compounds are promising organic
electron-transporting semiconductors for applications in field effect
transistors. Here, we investigated the electronic properties of
1,3,8,10-tetraazaperopyrene derivatives adsorbed on Au(111) using a
complementary experimental approach, namely scanning tunneling spectroscopy and
two-photon photoemission combined with state-of-the-art density functional
calculations. We find signatures of weak physisorption of the molecular layers,
such as the absence of charge transfer, a nearly unperturbed surface state and
an intact herringbone reconstruction underneath the molecular layer.
Interestingly, molecular states in the energy region of the \emph{sp}- and
\emph{d}-bands of the Au(111) substrate exhibit hole-like dispersive character.
We ascribe this band character to hybridization with the delocalized states of
the substrate. We suggest that such bands, which effectively leave the
molecular frontier orbitals largely unperturbed, to be a promising lead for the
design of organic-metal interfaces with a low charge injection barrier.
