Tunneling-electron-induced molecular luminescence from a nanoscale layer of organic molecules on metal substrates

Molecular luminescence from an ultrathin layer of free-base porphyrin molecules has been generated by a scanning tunneling microscope on top of a monolayer spacer of perinone derivatives on Cu(100). Tunneling-electron-induced fluorescence spectra are in good agreement with the conventional photoluminescence data of the molecule. The dominant molecular luminescence peak becomes clear and sharp for bias voltages above similar to2.1 V. The perinone monolayer does not emit light because of quenching effects; it acts as a buffer layer to enhance the decoupling of the electronic state of the porphyrin molecules from the Cu substrate. The molecular luminescence from porphyrin is attributed to the hot electron injection excitation. These results demonstrate the feasibility of electrically driven molecular luminescence on metal substrates by a nanoscale probe. (C) 2004 American Institute of Physics.