Paper SS2-MoA1
Self-assembled Chains of 4,4’-azopyridine on Cu(100) Stabilized by Metal-Organic Coordination Interactions

Monday, October 31, 2011, 2:00 pm, Room 110

Understanding self-assembled molecular architectures at surfaces is essential to control and tune low-dimensional nanometer-scale organic structures. 4,4’-azopyridine (APY) has been vapor deposited on the clean Cu(100) surface in ultra-high vacuum and investigated using scanning tunneling microscopy and X-ray photoelectron spectroscopy. APY is chosen as a model building block for metal-organic frameworks, and for its conformational switching by the photoactive azo bridge. At low coverage, APY self-assembles into highly-ordered one-dimensional chains oriented along the low symmetry directions of the surface, many of which grow from the Cu step edges and some of which form tee junctions with other chains. Careful analysis of high resolution STM images points to pyridyl-Cu interactions being responsible for the high chain stability at room temperature. The related molecule, azobenzene, forms 1D chains on Au(111), but these grow side-to-side by hydrogen bonding at the azo bridge nitrogens and are only observed at cryogenic temperatures [1]. At higher coverages, APY chains align in a parallel fashion to form 2D islands, which increase in size with annealing.

[1] A. Kirakosian, M. J. Comstock, J. Cho, M. F. Crommie, Phys. Rev. B 71, 113409 (2005).