  Interfacial electron transfer (IET) dynamics in 1,1'-dioctadecyl-3, 3, 3',
3'-tetramethylindodicarbocyanine (DiD) dye molecules / indium tin oxide (ITO)
film system have been probed at the ensemble and single-molecule level by
recording the change of fluorescence emission intensity. By comparing the
difference of the external electric current (EEC) dependence of lifetime and
intensity for enambles and single molecules, it is shown that the
single-molecule probe can effcienly demonstrate the IET dynamics. The backward
electron transfer and electron transfer of ground state induce the single
molecules fluorescence quenching when an EEC is applied to ITO film.
