The discovery of organic semiconductors. Its light and shadow

In this article I report why and how I became engaged in the study of organic semiconductors. My first step in the investigation of organic semiconductors was the measurement of electrical resistance of powdered carbon materials, which is a sort of solid colloid. Through the observation of electrical resistance of carbons, I accepted the property that carbon particles certainly conduct electric current. There, however, still remained a question as to how an electron could leap from one particle to another. I noticed that functional groups bound to the edges of polycyclics in graphite do not cause swelling. Then, I hit upon an idea that polycyclic aromatic compounds with molecular structures similar to fragments of graphite might be electrically conductive. So I started by measuring the electrical resistance of violanthrone, a molecule containing nine benzene rings, with laborious experiments and hence found semiconductive behaviour in organic solids (1954). In this article, I also report my encounter with charge transfer type organic semiconductors. (C) 2006 Elsevier B.V. All rights reserved.