Fusion of three benzene rings in a triangular fashion
gives rise
to the smallest open-shell graphene fragment, the phenalenyl radical,
whose π-extension leads to an entire family of non-Kekulé
triangular nanographenes with high-spin ground states. Here, we report
the first synthesis of unsubstituted phenalenyl on a Au(111) surface,
which is achieved by combining in-solution synthesis of the hydro-precursor
and on-surface activation by atomic manipulation, using the tip of
a scanning tunneling microscope. Single-molecule structural and electronic
characterizations confirm its open-shellS= 1/2
ground state that gives rise to Kondo screening on the Au(111) surface.
In addition, we compare the phenalenyl’s electronic properties
with those of triangulene, the second homologue in the series, whoseS= 1 ground state induces an underscreened Kondo effect.
Our results set a new lower size limit in the on-surface synthesis
of magnetic nanographenes that can serve as building blocks for the
realization of new exotic quantum phases of matter.