Variations in Complementary Hydrogen Bonds Direct Assembly Patterns of Isosteric Polyheteroaromatics at Surfaces

Intermolecular interactions guide self-assembly on the surface. Precise control over these interactions by rational design of the molecule should allow fine control over the self-assembly patterns. Functional groups installed for electronic modulation often induce significant changes in the molecular dimensions, thereby disrupting the original assembly pattern. To overcome this challenge, we have employed a family of isosteric phenazine derivatives, DHP, DAP, and DBQD, to investigate the impacts of hydrogen bonding on two-dimensional molecular self-assembly. While these molecules are similar in size and chemical composition, the strength and directionality of hydrogen bonding differ significantly depending on the chemical structure of donor-acceptor pairs and prototropic tautomerization from positional isomerism. Scanning tunneling microscopy (STM) characterization of the assembled structures on Ag(111), Au(111), and Cu(100) surfaces revealed that minimal changes in molecular structure have a profound impact on the self-assembly patterns. While DHP exhibits highly ordered and robust assemblies, DAP and DBQD show either spatially confined or ill-defined assemblies. In conjunction with hydrogen bonding, prototropic tautomerism is a potent strategy to modulate molecular 2D lattices on surfaces.