Molecular junctions consisting of a Ru(bpy)(3) oligomer between conducting carbon contacts exhibit an exponential dependence of junction current on molecular layer thickness (d) similar to that observed for other aromatic devices when d < 4 nm. However, when d > 4 nm,, a change in: transport mechanism, Occurs which coincides with light emission in the range of 600-900 nm. Unlike light emission from electrochemical cells or solid-state films containing Ru(bpy)(3), emission is bipolar, occurs in vacuum, has-rapid rise time (<5 ms), and persists for >10 h. Light emission directly indicates simultaneous hole and electron injection and transport, possibly resonant due to the high electric field present (>3 MV/cm). Transport differs fundamentally from previous tunneling and hopping mechanisms and is a clear "molecular signature" relating molecular Structure to electronic behavior.