Fluorescence quenching of CdSe-ZnS quantum dots (core-shell QDs) is shown to be affected in the presence of cobalt(III) complexes with pyridyl anchors. Steady-state and time-resolved fluorescence spectra indicate that the quenching has primarily a static component. The decrease in photoluminescence intensity can be best explained by charge transfer from the QDs to the Co(III) complexes whereas the energy transfer pathways have been methodically ruled out. The fact that quenching is a result of electron transfer is also supported by electrochemical data showing the positions of the energy levels.