  Bridged triarylamines, so-called N-heterotriangulenes (N-HTAs) are promising
organic semiconductors for applications in optoelectronic devices. Thereby the
electronic structure at organic/metal interfaces and within thin films as well
as the electronically excited states dynamics after optical excitation is
essential for the performance of organic-molecule-based devices. Here, we
investigated the energy level alignment and the excited state dynamics of a
N-HTA derivative adsorbed on Au(111) by means of energy- and time-resolved
two-photon photoemission spectroscopy. We quantitatively determined the
energetic positions of several occupied and unoccupied molecular (transport
levels) and excitonic states (optical gap) in detail. A transport gap of 3.20
eV and an optical gap of 2.58 eV is determined, resulting in an exciton binding
energy of 0.62 eV. With the first time-resolved investigation on a N-HTA
compound we gained insights into the exciton dynamics and resolved processes on
the femtosecond to picosecond timescale.
