2H-TPP on Ag: carbon de-hydrogenation
Formation of a monolayer of 2H-tetraphenylporphyrins (2H-TPP) on Ag(111), either by sublimation of a multilayer in the range 525–600 K or by annealing (at the same temperature) a monolayer deposited at room temperature, induces a chemical modification of the molecules. We observe a selective carbon de-hydrogenation with the formation of new aryl-aryl bonds between phenyl groups as well as their rotation in a flat conformation. G. Di Santo et al., Chem. - A Europ J. 17(51), 14354-9 (2011)|
In our recent investigations we have demonstrated that one monolayer of 2H-TPP, prepared by thermal desorption of the corresponding multilayer at 550 K on Ag(111), adsorbs with the macrocycle and the phenyl flat. This information has been directly addressed by means of X-ray absorption and photoemission experiments.
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Theoretical calculations suggest a possible molecular reaction and modification of porphyrins, in order to explain this adsorption conformation: the de-hydrogenation of eight carbon atoms in the remaining monolayer after the multilayer desorption, with the formation of four new aryl-aryl carbon bonds. While the reaction takes place also in the deposited monolayer annealed at 550 K, the initial presence of the multilayer favors a decrease of the aryl-aryl coupling barrier and the selection of a spiral conformation in the de-hydrogenated molecule. The chemical reaction produces a stable molecule that forms a patterned square lattice on Ag(111) and that can be further modified by the introduction of central metal atoms.
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 Retrieve article Supramolecular Engineering through Temperature-Induced Chemical Modification of 2H-Tetraphenylporphyrin on Ag(111): Flat Phenyl Conformation and Possible Dehydrogenation Reactions
Chemistry - A European Journal vol 17, Issue 51, pages 14354–14359, December 16, 2011 |
