Two-dimensional assemblies of saccharide-derived molecules on highly oriented pyrolytic graphite revealed by scanning tunneling microscopy

Saccharides play important roles as structural components of plants and for molecular recognition in living organisms, and they are increasingly being used as environmentally-friendly bio-based materials. In this study, two-dimensional (2D) assemblies of 1,5-anhydro-D-glucitol (AG) derivatives were examined by scanning tunneling microscopy at the highly oriented pyrolytic graphite (HOPG)/solvent interface. The effects of the solvent, alkyl chain linkage, and alkyl chain length on the 2D structures were investigated. Grid-like and columnar structures were periodically formed depending on the odd-even nature of the carbon atoms in the alkyl chain unit, highlighting the importance of in-plane intermolecular interactions between adsorbed molecules in determining the 2D molecular arrangement. The calculated adsorption energies for the alkyl chain and pyranose ring units with the graphene model indicated that the former was significantly greater than the latter. Despite the strong interactions between adsorbates and substrate, relatively weak in-plane interactions between adsorbates result in the 2D molecular arrangements of the AG derivatives.