Determining transmission characteristics from shot-noise-driven electroluminescence in single-molecule junctions

Biased metal–molecule–metal junctions emit light through electroluminescence, a phenomenon at the intersection of molecular electronics and nanoplasmonics. This can occur when the junction plasmon mode is excited by inelastic electron current fluctuations. Here, we simultaneously measure the conductance and electroluminescence intensity from single-molecule junctions with time resolution in a solution environment at room temperature. We use current versus bias data to determine the molecular junction transport parameters and then relate these to the expected current shot noise. We find that the electroluminescence signal accurately matches the theoretical prediction of shot-noise-driven emission in a large fraction of the molecular junctions studied. This introduces a novel experimental method for qualitatively estimating finite-frequency shot noise in single-molecule junctions under ambient conditions. We further demonstrate that electroluminescence can be used to obtain the level alignment of the frontier orbital dominating transport in the molecular junction.