Standing up versus looping over: controlling the geometry of self-assembled monolayers of α,ω-diynes on gold.

It is shown that self-assembled monolayers (SAMs) composed of α,ω-diynes on gold have different structures depending on the concentration of molecules used to make the SAM. Evidence for both hairpinned and standing-up molecules is provided. This behavior is in contrast to SAMs of α,ω-dithiols on gold, which generally form SAMs with only the straight conformation. The looped SAMs composed of α,ω-diynes offer a less densely packed and thus somewhat accessible surface that may be useful when the underlying surface is used as an electrode. Furthermore, biasing the structure of the molecules in the SAM between looped and standing-up may be useful in the design of dynamic surfaces.