cfaed Seminar Series

The polymerization of organic monomers on solid surfaces is a promising and versatile
synthetic route for the bottom-up fabrication of 2D polymers. Various coupling reactions
are successfully employed for the on-surface synthesis of extended covalent
nanostructures that are inaccessible by other synthetic means. Yet, many important
reactions, as for instance Ullmann coupling, normally proceed irreversibly. Consequently,
the lack of error correction mechanisms during growth inevitably results in networks with
high defect densities.
In contrast, supramolecular self-assembly based on reversible intermolecular interactions
is well-known to yield networks with high structural quality. The presentation introduces
and discusses different concepts, how bond reversibility and non-covalent self-assembly
can also be utilized for the on-surface synthesis of covalent nanostructures: A more
obvious option is the use of coupling reactions that can proceed reversibly as for instance
boronic acid condensation. Yet, on the appropriate surface even a notoriously irreversible
reaction as Ullmann coupling can exhibit an organometallic intermediate featuring bond
reversibility. We will demonstrate that equilibration of these organometallic intermediates is
advantageous to improve the structural quality of covalent networks. Lastly, the most
elegant, but most specialized option is to firstly use non-covalent interactions for preassembling
an ordered structure, and to secondly induce covalent cross-linking while
maintaining this initial arrangement. A topochemical photopolymerization on a solid
surface will be discussed as an implementation of this principle.