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Chiral switching by spontaneous conformational change in adsorbed organic molecules

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Abstract

Self-assembly1,2 of adsorbed organic molecules is a promising route towards functional surface nano-architectures, and our understanding of associated dynamic processes has been significantly advanced by several scanning tunnelling microscopy (STM) investigations3,4,5,6,7. Intramolecular degrees of freedom are widely accepted to influence ordering of complex adsorbates, but although molecular conformation has been identified8 and even manipulated9,10,11 by STM, the detailed dynamics of spontaneous conformational change in adsorbed molecules has hitherto not been addressed. Molecular surface structures often show important stereochemical effects as, aside from truly chiral molecules12,13,14,15, a large class of so-called prochiral molecules16,17,18,19 become chiral once confined on a surface with an associated loss of symmetry. Here, we investigate a model system in which adsorbed molecules surprisingly16 switch between enantiomeric forms as they undergo thermally induced conformational changes. The associated kinetic parameters are quantified from time-resolved STM data whereas mechanistic insight is obtained from theoretical modelling. The chiral switching is demonstrated to enable an efficient channel towards formation of extended homochiral surface domains. Our results imply that appropriate prochiral molecules may be induced (for example, by seeding) to assume only one enantiomeric form in surface assemblies, which is of relevance for chiral amplification and asymmetric heterogenous catalysis.

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Acknowledgements

We acknowledge the financial support from the EU programs FUN-SMART and AMMIST, as well as from the Carlsberg Foundation, the Danish Technical Research Council and from the Danish Natural Science Research Council through funding for the iNANO centre. We thank A. H. Thomsen and M. Nielsen for synthesizing the molecules.

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Competing interests

The authors declare no competing financial interests.

Correspondence to Trolle R. Linderoth.

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  1. Supplementary Information

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Further reading

Figure 1: Brick-wall adsorption structure.
Figure 2: Conformational changes for molecules in the brick-wall structure.
Figure 3: Structures from theoretical modelling.
Figure 4: Network adsorption structure and chiral accommodation.