The ruthenium dye N3, cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(ii), deposited on Ag(111) by ultra-high vacuum electrospray ionization is investigated using low-temperature scanning tunneling microscopy. Scanning tunneling spectroscopy of single molecules reveals vibronic excitations that are related to the lowest unoccupied molecular orbital (LUMO). Switching of N3 may be induced and modifies the energy of the negative ion resonance as well as the vibrational progression. Moreover, charging of the molecule is induced at reverse bias. These data suggest a surprisingly weak electronic coupling of N3 to the Ag substrate. A double-barrier model reproduces the essential spectral features.