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Covalent Organic Frameworks on Crystalline Surfaces

The synthesis of two-dimensional ordered structures is one major concern in materials science. Especially porous structures have gained a lot of interest due to possible applications as nanotemplates or storage materials. Molecular self-assembly is one way to create ordered structures. Due to the relatively weak intermolecular interactions bonds are reversible and therefore structures exhibit long range order. The disadvantage is the weakness of the bonds and hence the interior stability of the structure. Polymerization, i.e. the formation of covalent bonds would yield networks with desired mechanical stability. Besides, conjugated polymers might also give rise to very interesting electronic properties (semiconducting/metallic behaviour).

Picture 1: Annealing of a protopolymer leads to a polymer

Following the nature of the Ullmann dehalogenation reaction with the substrate as catalyst, the bromine atoms of the molecule 1,3,5-tris(4-bromophenyl)benzene (TBB) are replaced by metal atoms and interlink into metal-coordinated networks. Thermal  annealing is necessary to finally convert the bonds into covalent bonds. This is accompanied by a contraction of the intermolecular distance. The polymers could be prepared on Cu(111) and on Ag(110) surfaces.

Picture  2: Protopolymers before annealing

Picture 3: covalent organic frameword after annealing of the protopolymer

Further Reading:

Surface mediated synthesis of 2D covalent organic frameworks: 1,3,5-tris(4-bromophenyl)benzene on graphite(001), Cu(111), and Ag(110)

Rico Gutzler, Hermann Walch, Georg Eder, Stephan Kloft, Wolfgang M. Heckl, and Markus Lackinger, Chem. Commun., 2009, 4456-4458.

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