Subtle Fluorination of Conjugated Molecules Enables Stable Nanoscale Assemblies on Metal Surfaces

In
molecular self-assembly on surfaces, the structure is governed by
the intricate balance of attractive and repulsive forces between molecules
as well as between molecules and the substrate. Frequently, repulsive
interactions between molecules adsorbed on a metal surface dominate
in the low-coverage regime, and dense self-assembled structures can
only be observed close to full monolayer coverage. Here, we demonstrate
that fluorination at selected positions of conjugated molecules provides
for sufficiently strong, yet nonrigid, H···F bonding
capability that (i) enables the formation of stable nanoscale molecular
assemblies on a metal surface and (ii) steers the assemblies’
structure. This approach should be generally applicable and will facilitate
the construction and study of individual nanoscale molecular assemblies
with structures that are not attainable in the high-coverage regime.