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Abstract:
One of the fundamental goals in Chemistry is to understand why certain molecules exhibit specific properties and functions. Central to this problem is the need to elucidate how molecules move and interact. Here, I probe these dynamics at the single molecule level by imaging individual molecules on surface using Scanning Tunnelling Microscopy (STM) corroborated by ab initio calculations.
For simple molecules, a difluorocarbene (CF2) radical was aimed at co-adsorbed species to enable for the first time the study of bimolecular reactions as a function of an important but elusive quantity, the impact parameter, b (the distance by which a ‘projectile’ misses the ‘target’ molecule). The CF2 projectile, generated by dissociating its parent CF3 molecule on surface, was collided at a CF2 target and a vinyl target to reveal in each cases the reactive and non-reactive scattering channels. This approach enables a molecular projectile to be aimed with selected impact parameter in scattering experiments to any target species at a surface.
For complex molecules, glycans (a.k.a oligosaccharides or carbohydrates) were imaged to reveal the glycan structure, whose elucidation by ensemble-averaged technique is very challenging due to the high flexibility of glycans. Imaging glycans reveal their degree of branching, their diverse conformation states, and their flexibility at single linkage level. Examining the flexibility of cellohexaose and its chemically substituted analogues reveals how glycan flexibility is tuned by its primary structure (i.e. sequence) and secondary structure (i.e. conformation). The approach here enables structure-property relationship to be established at atomic level for any molecules that can be deposited onto surface.