KANAZAWA, Japan, Dec. 17, 2021 /PRNewswire/ — Researchers at Kanazawa University report in ChemComm the visualization of polymers with helical structures. By means of atomic force microscopy, they were able to elucidate the precise difference between molecules that are structurally very similar but have totally different color and luminescent properties.
Optically active molecules, also known as enantiomers, are pairs of molecules that are each other’s mirror image — like a person’s left and right hand. Often, enantiomeric molecules feature helices, with the ‘left-‘ or ‘right-handedness’ being related to how a helix coils. Visualizing the helical structures in complex organic molecules is important for understanding their chiral (‘handedness’-related) properties, and for the design of materials exploiting these. Now, Katsuhiro Maeda and colleagues from Kanazawa University have succeeded in visualizing the helical structure of an important set of polymers with chiral constituents.
The molecules investigated by Maeda and colleagues belong to the group of poly(diphenylacetylene)s (PDPAs), chemically and thermally stable polymers with excellent photoluminescent properties, making them promising functional materials. The researchers studied the helical structures in PDPAs bearing chiral amide pendants by means of high-resolution atomic-force microscopy (AFM).
AFM is a technique in which a very small tip, attached to a cantilever, is made to scan a sample’s surface. The tip’s response to height differences in the scanned surface provides structural information of the sample. For their AFM investigation of PDPAs, the research team put the molecules on a substrate known as highly oriented pyrolytic graphite (HOPG), a very pure and highly ordered form of synthetic graphite. The PDPA molecules self-assembled into a closely packed layer on the HOPG substrate, making it possible to observe not just one but a whole domain of molecules (Figure 1).
By using AFM, the researchers were able to observe structural differences between two particular PDPA diastereomers that were previously shown to have different colors …