Thermally activated transformation of the adsorption configurations of a complex molecule on a Cu(111) surface

Temperature-dependent transformations of the adsorption configuration of a molecule containing 2,2′:6′,2″-terpyridine (terpy) end-groups on a flat Cu(1 1 1) surface are studied by a combination of scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. Several quite different adsorption configurations are detected for the terpy end-group, including flat physisorption, distorted chemisorption through N–Cu bonds, and H-dissociative chemisorption through N–Cu and C–Cu bonds. These illustrate and explore various bonding modes of molecules at surfaces, which also imply a greater richness of reaction pathways, both of which are of central importance in a wide variety of heterogeneous catalytic processes on metal catalysts. As deposited on the cold substrate (near 77 K), the molecules are preferably chemisorbed on the surface through N–Cu bonds. With increasing annealing temperature, the molecules are converted to a physisorption configuration at and above 300 K, and above 370 K a small fraction of molecules undergoes dehydrogenation and chemisorb on the surface through N–Cu and C–Cu bonds. The present study demonstrates that the combination of STM measurements and DFT calculations is very effective for probing the atomic details of molecular adsorption configurations on surfaces.