Real-Space Identification of Intermolecular Bonding with Atomic Force Microscopy

Imaging Hydrogen Bonds The decoration of atomic force microscope tips with terminal CO molecules has afforded much higher resolution of the bonding of adsorbed molecules. Zhang et al. (p. 611, published online 26 September) show that this method, in combination with density function theory calculations, can image and characterize hydrogen-bonding contacts formed between 8-hydroxyquinoline molecules adsorbed on the (111) surface of copper under cryogenic conditions. At room temperature, a different bonding configuration was revealed that was the result of the molecules dehydrogenating on the copper surface and coordinating with surface copper atoms. An atomic force microscope tip bearing a single carbon monoxide molecule was used to resolve hydrogen-bonding contacts between molecules. We report a real-space visualization of the formation of hydrogen bonding in 8-hydroxyquinoline (8-hq) molecular assemblies on a Cu(111) substrate, using noncontact atomic force microscopy (NC-AFM). The atomically resolved molecular structures enable a precise determination of the characteristics of hydrogen bonding networks, including the bonding sites, orientations, and lengths. The observation of bond contrast was interpreted by ab initio density functional calculations, which indicated the electron density contribution from the hybridized electronic state of the hydrogen bond. Intermolecular coordination between the dehydrogenated 8-hq and Cu adatoms was also revealed by the submolecular resolution AFM characterization. The direct identification of local bonding configurations by NC-AFM would facilitate detailed investigations of intermolecular interactions in complex molecules with multiple active sites.