Heptagonal Molecular Tiling via Self-Assembly of Heptagonal Phenylene-Ethynylene Macrocycle at the Liquid-Solid Interface.

The molecular-level scrutinization of on-surface tiling garners considerable interest among scientists. Herein, we demonstrate molecular-level heptagonal tiling using the self-assembly of a heptagonal meta-phenylene-ethynylene macrocycle featuring 14 long alkoxy substituents at the liquid-graphite interface using scanning tunneling microscopy. This heptagonal macrocycle produces an antiparallel pattern at the 1-phenyloctane-graphite interface through van der Waals interactions between the alkoxy chains. This pattern resembles the densely packed pattern of heptagonal tiles, albeit with variations in the orientations and spacing of heptagonal cores owing to intermolecular interactions between the alkoxy chains. Conversely, at the 1,2,4-trichlorobenzene-graphite interface, the heptagonal molecule forms an oblique pattern composed of four independent molecular orientations. This phenomenon arises from core distortion induced by the coadsorption of the solvent molecules within the intrinsic macrocyclic pores. This study elucidates the design strategy - specifically, the choice of heptagonal molecular building block - for heptagonal tiling and fills a crucial gap in the field of two-dimensional crystal engineering.