Iterative Synthesis of Pyrene-Coronene Molecular Graphene Nanoribbons

The synthesis of molecular, or monodisperse, graphene nanoribbons with full atomic precision is essential for establishing fundamental structure-property relationships, validating theoretical predictions, and meeting the property requirements for the diverse potential applications of graphene nanoribbons. The synthesis of undoped molecular graphene nanoribbons remains challenging, as many edge topologies have yet to be realized and the reported structures still exhibit limited lengths. This is mostly because iterative synthetic methods for undoped molecular GNRs remain practically undeveloped, with current approaches relying predominantly on noniterative strategies. The iterative synthesis of a new family of undoped molecular GNRs, featuring both a novel edge topology and an unprecedented length, is reported. These nanoribbons are accessed through a borylation/Suzuki/cyclodehydrogenation reaction sequence, in which the Suzuki and cyclodehydrogenation are merged into one transformation, giving rise to an effective two-step iteration sequence. The resulting pyrene-coronene graphene nanoribbons exhibit strong absorption and high fluorescence efficiency, with molar absorptivity and fluorescence brightness values on the order of 10⁵ M^-1 cm^-1, and an intrinsic charger carrier mobility of 475 ± 32 cm² V^-1 s^-1.