Resolving Solution-Synthesized Graphyne-Graphdiyne Macromolecules at the Angstrom Level

Syntheses of low-dimensional macromolecules with increasing size and complexity in solution pose substantial challenges in terms of their precise structural characterization. Electrospray ionization coupled with scanning tunneling microscopy (ESI-STM) has emerged as a promising tool for the characterization of these nonsublimable macromolecules in real space. However, the weak ionization of such macromolecules and the three-dimensional configuration of the attached solubilizing groups severely impede high-resolution STM imaging. In this work, we synthesized a series of graphyne-graphdiyne concentric macrocycles with triphenylamine groups to enhance the ionization efficiency, which in turn ensures the sample cleanliness for STM characterization. To tackle imaging interference from solubilizing groups, single-molecule tip manipulation and large-scale bromine-assisted thermal treatment were developed for alkoxy and/or alkyl chain removal, enabling the acquisition of unprecedented bond-resolving structural images and angstrom-resolution frontier molecular orbital maps. Our methods resolve the long-standing dilemma between the solubility requirements of solution synthesis and the molecular planarization demands of high-resolution STM characterization, pushing the resolution limit of macromolecules to the angstrom level.