Electronic Interaction between Submonolayer Molecular Films and Substrates of Different Nature

: The electronic interaction between UHV-deposited organic molecules (MePTCDI) and ultraclean insulating, semiconducting, and metal substrates (quartz, Ag, Si) is investigated. By means of submonolayer coverage (0.01 monolayer) intermolecular interaction is suppressed and quenching of molecular excitation is studied directly by analyzing the fluorescence lifetime as a function of the distance between molecule and substrate. The quenching on Ag(111) can quantitatively be described by the classical image dipole theory (CPS), implying interaction with the charge carriers in the metal. Quenching on the semiconductor Si(111) is much less effective and is explained by creation of electron/hole pairs in the substrate.