Complex single‐molecule and molecular scale entities in electrochemical environments:Mechanisms and challenges

Following a renaissance from the 1980s, electrochemistry has developed into sophisticated interdisciplinary science integrating solid-state and surface science and further, biological sciences. Most remarkably, even the single-molecule can now be addressed. Single-molecule electrochemistry covers transition metal complexes, organic redox molecules, fragile biomolecules, and molecular-scale hybrids between metallic nanoparticles and complex molecules, supported by new theoretical frames. We overview here selected areas of molecular scale electrochemistry. After a theoretical minimum, we address complex molecules in electron transfer, enzyme catalysis, and nanoparticle catalysis. Our focus is on issues not so much previously highlighted, such as competition between superexchange and sequential conduction, and resonance features in the transition between the two limits. Another aspect is coherent multi-electron transfer for large bias voltages often needed to drive enough current through solute molecular junctions. We note finally some single-molecule perspectives relating to DNA-based molecules and to spin transitions via chiral molecules.