Role of molecules in tunneling-current-induced photon emission from the surface of a perinone derivative molecular monolayer on Au(100)

The role of molecules in tunneling current induced photon emission from luminescent molecules on metal surfaces is still an open issue despite the recent observation of molecular fluorescence. We found that at low tunneling currents (<1 nA), the molecular fluorescence from the surface of a perinone derivative (PD) molecular monolayer on Au(100) is completely quenched through non-radiative energy dissipation to the Au substrate. The PD molecular monolayer acts as a spacer to modify the tip-induced plasmon modes, enhance the intensity of the plasmon-mediated emission, and cause a blueshift of the emission spectra. However, at relatively high tunneling currents (1 nA<I-t<similar to5 nA), broadened emission spectra were observed, which suggests that molecular fluorescence may be feasible upon further decoupling of the PD molecular electronic states from the metal substrate.