STM-excited molecular fluorescence from MEH-PPV conjugated polymer on Ag and Au

We studied the scanning tunneling microscope-induced luminescence (STML) of conjugated polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PPV) spun from the solutions with various concentrations on metal substrates Ag and Au. Characteristic molecular fluorescence with the intrinsic molecular vibronic peaks associated with the HOMO–LUMO transition appears in addition to the curve based on plasmon-mediated light emission from the metal substrate Ag or Au. We found that it is a necessary condition to observe molecular fluorescence that the plasmon-mediated light from the metal substrate, which depends on the substrate, is intense in the absorption band of the molecule.