Binary Conformational Switches in a Porphyrin Chain: Tautomerization and Stereoisomerization

In the last decade, hydrogen (H-)tautomerization, that is, a reaction that involves simple intramolecular proton transfer, has been studied in single phthalocyanine, porphyrin, and porphycene derivatives as a prototypical single molecular conductance switch. Here, by means of low-temperature scanning tunneling microscopy and density functional theory calculations, we report a binary H-tautomerism and stereoisomeric conformational switch in (amino-functionalized) porphyrins assembled in molecular chains on a gold surface. We show that the formation of the chain is crucial for the binary tautomeric switch mechanism as the single molecule switches differently. Our findings suggest that the (amino-)functionalization of molecules can be exploited not only to drive the formation of molecular self-assemblies but also to steer their switching properties.