Development and Application of Polycyclic Conjugated Systems Bearing a Pentalene Skeleton

Recently, polycyclic conjugated systems bearing carbocyclic five-membered rings have attracted much attention because of their utility in organic electronic devices. Despite possessing a 4nπ electron periphery, dibenzopentalenes are fairly stable compounds with a planar structure. Thus, appropriate modification would provide them with desirable electronic properties. Recently we found novel reactions yielding dibenzopentalene derivatives from readily available o-bromoethynylbenzenes using commercially available nickel complexes, and from 2-bromotolans via a novel amino migration reaction. These methods are accessible to π-extended pentalene derivatives bearing various functional groups and aromatic ring systems. Among them, a dinaphthylpentalene derivative showed very high hole mobility (1.8×10−3 cm2V−1s−1) as amorphous materials. Furthermore, it was employed as a p-type material for organic heterojunction photovoltaic cells (PCE=0.94%, Voc=0.96 V). It is the first pentalene derivative for organic thin-film semiconductors.