  Triangular zigzag nanographenes, such as triangulene and its pi-extended
homologues, have received widespread attention as organic nanomagnets for
molecular spintronics, and may serve as building blocks for high-spin networks
with long-range magnetic order - of immense fundamental and technological
relevance. As a first step toward these lines, we present the on-surface
synthesis and a proof-of-principle experimental study of magnetism in
covalently bonded triangulene dimers. On-surface reactions of
rationally-designed precursor molecules on Au(111) lead to the selective
formation of triangulene dimers in which the triangulene units are either
directly connected through their minority sublattice atoms, or are separated
via a 1,4-phenylene spacer. The chemical structures of the dimers have been
characterized by bond-resolved scanning tunneling microscopy. Scanning
tunneling spectroscopy and inelastic electron tunneling spectroscopy
measurements reveal collective singlet-triplet spin excitations in the dimers,
demonstrating efficient inter-triangulene magnetic coupling.
