Electroluminescence spectra in weakly coupled single-molecule junctions

We have combined ab initio quantum chemistry calculations with a rate-equation formalism to analyze electroluminescence spectra in single-molecule junctions, measured recently by several groups in scanning tunneling microscope setups. In our method, the entire vibrational spectrum is taken into account. Our method leads to good quantitative agreement with both the spectroscopic features of the measurements and their current and voltage dependence. Moreover, our method is able to explain several previously unexplained features. We show that in general, the quantum yield is expected to be suppressed at high bias, as is observed in one of the measurements. Additionally, we comment on the influence of the vibrational relaxation times on several features of the spectrum.