We report the evolution of the electronic structure of excited (sub)monolayer films of vanadyl naphthalocyanine (VONc) at the interface with highly oriented pyrolytic graphite (HOPG). Using two-photon photoemission spectroscopy, an unoccupied state corresponding to the lowest unoccupied molecular orbital of VONc is observed. The energy of this state shows a significant dependence on coverage, interpreted in the context of the electrostatic environment at the interface. On the basis of a simple electrostatic model, we were able to determine the excited-state polarizability and dipole moment of VONc at the interface with HOPG. The results suggest that local electric fields may have a major influence on interfacial energy level alignment in the excited-state manifold, with direct consequences for interfacial charge-transfer dynamics.
ASJC Scopus subject areas
- General Materials Science
- Physical and Theoretical Chemistry