On-surface synthesis has revolutionized the construction of functional nanostructures. Thus far, however, the concept of polymer tacticity has remained unexplored in this context. Tacticity impacts polymer properties, which in turn governs polymer applications. An all-syn arrangement of substituents in isotactic polymers, for instance, may lead to highly crystalline, high-strength materials. Thus, specialized methods have been developed involving chiral catalysts or ligands to control polymer tacticity. In this work, we demonstrate that two-dimensional surface confinement of on-surface polymerization can be combined with preorganization of monomers to synthesize isotactic polymer chains in the absence of a chiral auxiliary. To establish the concept, we synthesized a corannulene-substituted terphenylene monomer capable of C-H···π bonding, aromatic stacking, and van der Waals interactions. The weak intermolecular interactions steer the monomer into organized double strands, with the corannulene substituents oriented only on one side of the strand on Ag(111). A subsequent Ullmann polymerization of the self-assembled monomers leads to the formation of double-stranded isotactic polyphenylenes. The stereoregularity further allows the duplex to arrange into higher-order crystalline domains. Finally, the synthetic polymer duplex can be mechanically unzipped into individual isotactic polymer chains through scanning tunneling microscopy tip manipulation.
Dong et al. (Mon,) studied this question.