Dynamic helical poly[4]helicene nanoribbon

The precise synthesis of helical graphene nanoribbons (GNRs) with a controlled handedness has a transformative potential as the promising chiral carbon materials. We now report the first synthesis of a dynamic helical poly[4]helicene nanoribbon, a novel class of helical GNRs, entirely composed of configurationally labile [4]helicene subunits, which has been achieved through the quantitative intramolecular multifold cyclization of the nonhelical precursor polymer. The [4]helicene repeating units of the poly[4]helicene nanoribbon are mechanically coupled to each other, providing an equal mixture of an interconvertible long sequence of right (P)- and left (M)-handed helical [4]helicene subunits. Therefore, in an optically-active solvent, a fully (P)- or (M)-helical poly[4]helicene nanoribbon consisting of homochiral (P)- or (M)-[4]helicene subunits can be induced in a highly-cooperative manner, showing a right- or left-handed circularly polarized luminescence, respectively, which can be switched.