Stepwise Lateral Extension of Phenyl‐Substituted Linear Polyphenylenes

Front Cover : In article number 1900374 by Akimitsu Narita, Klaus Müllen, and co‐workers, a new synthetic approach toward lateral extension of polyphenylenes is developed. This strategy bases on a stepwise Diels‐Alder reaction between cyclopentadienone‐based building blocks, and ethynyl groups rationally appended on a starting polyphenylene. The strategy enables syntheses of a series of laterally extended polymers, which can potentially serve as precursors of graphene nanoribbons wider than 2 nm.