Toward Molecular Nanowires Self-Assembled on an Insulating Substrate: Heptahelicene-2-carboxylic acid on Calcite (1014)

Molecular self-assembly is employed for creating unidirectional molecular nanostructures on a truly insulating substrate, namely the (101̅4) cleavage plane of calcite. The molecule used is racemic heptahelicene-2-carboxylic acid, which forms structures, well-aligned along the [010] crystallographic direction and stable at room temperature. Precise control of both molecule−substrate and molecule−molecule interaction is required, leading to the formation of such wire-like structures of well-defined width and lengths exceeding 100 nm. This subtle balance is governed by the heptahelicene-2-carboxylic acid used in this study, allowing for both hydrogen bond formation as well as π−π stacking.