Control of the Intermolecular Coupling of Dibromotetracene on Cu(110) by the Sequential Activation of CBr and CH bonds

by L. Ferrighi, I. Pìsˇ, T. H. Nguyen, M. Cattelan, S. Nappini, A. Basagni, M. Parravicini, A. Papagni, F. Sedona, E. Magnano, F. Bondino, C. Di Valentin and S. Agnoli
Chemistry: A European Journal 2015, Volume 21 (15), Pages 5826–5835                View at Publisher
DOI: 10.1002/chem.201405817

Dibromotetracene molecules are deposited on the Cu(110) surface at room temperature. The complex evolution of this system has been monitored at different temperatures (i.e., 298, 523, 673, and 723 K) by means of a variety of complementary techniques that range from STM and temperature-programmed desorption (TPD) to high-resolution X-ray spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). State-of-the-art density-functional calculations were used to determine the chemical processes that take place on the surface. After deposition at room temperature, the organic molecules are transformed into organometallic monomers through debromination and carbon-radical binding to copper adatoms. Organometallic dimers, trimers, or small oligomers, which present copper-bridged molecules, are formed by increasing the temperature. Surprisingly, further heating to 673 K causes the formation of elongated chains along the Cu(110) close-packed rows as a consequence of radical-site migration to the thermodynamically more stable molecule heads. Finally, massive dehydrogenation occurs at the highest temperature followed by ring condensation to nanographenic patches. This study is a paradigmatic example of how intermolecular coupling can be modulated by the stepwise control of a simple parameter, such as temperature, through a sequence of domino reactions.