Hexbyte Glen Cove
In a recent study published in Chemistry—A European Journal, a team of scientists at Tokyo Tech mixed things up by synthesizing a different type of organic molecule with a helical structure. Unlike helicenes, the basic unit of their compounds was anthracene, a linear chain of three aromatic rings. In previous works, the team had managed to synthesize HA, which stands for “helical anthracene with three anthracene units.” However, as Professor Shinji Toyota, the corresponding author of the study, explains, “HA was not long enough to reach a full turn. Therefore, it did not exhibit some of the peculiar characteristics that arise from the interactions between different ‘layers’ of the helical structure in a face-to-face fashion.”
Using a carefully planned step-by-step process, the scientists managed to synthesize HA and HA, which they proceeded to characterize through a variety of experiments backed by theoretical calculations. They verified the composition and structure of the compounds using proton nuclear magnetic resonance and X-ray analysis. These findings were confirmed through density functional theory calculations, a widely used approach used to make quantum mechanical models of electronic and nuclear structures.
Then, the researchers quantified the stability of the different helical anthracenes by using them in a virtual chemical reaction that changed them into flat molecules. Interestingly, the stability of 3[HA] was almost the same as that of HA and HA. This indicates that the destabilizing forces that naturally appear in longer molecular chains (HA and HA) actually canceled out with the new face-to-face stabilizing interactions between different helical layers. These interactions between layered anthracene moiety was visualized by Non-Covalent Interaction (NCI) analysis. The effect of these new interactions was also apparent in the photoemission properties of the longer molecules; their emission bands upon excitation were longer-lived, highlighting the fact that excited states were preserved longer.
Kei Fujise et al, Construction of Helical Structures with Multiple Fused Anthracenes: Structures and Properties of Long Expanded Helicenes, Chemistry – A European Journal (2020). DOI: 10.1002/chem.202004720
Coiling them up: Synthesizing organic molecules with a long helical structure (2021, January 29)
retrieved 1 February 2021
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