Electrochemical-chemical electron transfer in electrochromic nanoscale layers

We demonstrate here the assembly of a nanolayer of electrochromic iron complexes on top of composite layers of cobalt and ruthenium complexes. Depending on the ratio of the latter two complexes, we can tailor materials that show different elec-tron transport pathways, redox-activities, and color transitions. No redox activity of the top layer, consisting of iron com-plexes, is observable when the relative amount of the ruthenium complexes is low in the underlying composite layer because of the insulating properties of the isostructural cobalt complexes. Increasing the amount of ruthenium complexes opens an electron transport channel, resulting in charge storage both in the cobalt and iron complexes. The trapped charges can be chemically released by redox-active ferrocyanide complexes at the film-water interface, demonstrating an electrochemical-chemical electron transfer process.