Surface-assisted
Dehydrogenative Homocoupling of Porphine
Molecules
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Abstract
The templated synthesis of porphyrin
dimers, oligomers, and tapes
has recently attracted considerable interest. Here, we introduce a
clean, temperature-induced covalent dehydrogenative coupling mechanism
between unsubstituted free-base porphine units yielding dimers, trimers,
and larger oligomers directly on a Ag(111) support under ultrahigh-vacuum
conditions. Our multitechnique approach, including scanning tunneling
microscopy, near-edge X-ray absorption fine structure and photoelectron
spectroscopy complemented by theoretical modeling, allows a comprehensive
characterization of the resulting nanostructures and sheds light on
the coupling mechanism. We identify distinct coupling motifs and report
a decrease of the electronic gap and a modification of the frontier
orbitals directly associated with the formation of triply fused dimeric
species. This new on-surface homocoupling protocol yields covalent
porphyrin nanostructures addressable with submolecular resolution
and provides prospective model systems towards the exploration of
extended oligomers with tailored chemical and physical properties