Stable hydrocarbon radicals are able to withstand ambient
conditions.
Their combination with a supporting surface is a promising route toward
novel functionalities or carbon-based magnetic systems. This will
remain elusive until the interplay of radical–radical interactions
and interface effects is fundamentally explored. We employ the tip
of a low-temperature scanning tunneling microscope as a local probe
in combination with density functional theory calculations to investigate
with atomic precision the electronic and geometric effects of a weakly
interacting metal support on an archetypal hydrocarbon radical model
system, i.e., the exceptionally stable spin-1/2 radical α,γ-bisdiphenylene-β-phenylallyl
(BDPA). Our study demonstrates the self-assembly of stable and regular
one- and two-dimensional radical clusters on the Au(111) surface.
Different types of geometric configurations are found to result from
the interplay between the highly anisotropic radical–radical
interactions and interface effects. We investigate the interaction
mechanisms underlying the self-assembly processes and utilize the
different configurations as a geometric design parameter to demonstrate
energy shifts of up to 0.6 eV of the radicals’ frontier molecular
orbitals responsible for their electronic, magnetic, and chemical
properties.