Dynamic helical poly[4]helicene nanoribbon.

The precise synthesis of helical graphene nanoribbons (GNRs) with a controlled handedness represents a significant advance toward chiral carbon materials. We now report the synthesis of a dynamic helical poly[4]helicene nanoribbon, a 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, leading to correlated helicity inversion dynamics along the highly constrained ladder framework and thereby 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.