An Overview of Organic Charge-Transfer Solids: Insulators, Metals, and the Neutral-Ionic Transition

This presents a simple framework for studying the basic properties of the broad class of organic charge-transfer solids. It is shown that many of the differences in behavior of these materials can be described and understood in terms of a single, physical variable: δEREDOX, the difference between the electrochemical oxidation potential of the donor and the reduction potential of the acceptor. Differences in this parameter are shown to be largely responsible for the difference between organic metals and insulators. δEREDOX also determines whether the solids are neutral or ionic and has led to the discovery of a neutral-ionic transition between these two types of ground states.