[1][page needed] The molecules may be shifted between the states in response to environmental stimuli, such as changes in pH, light, temperature, an electric current, microenvironment, or in the presence of ions[2] and other ligands.
Robert Boyle was the first person to describe this effect, employing plant juices (in the forms of solution and impregnated paper).
[6] A widely studied class are photochromic compounds which are able to switch between electronic configurations when irradiated by light of a specific wavelength.
Although not strictly speaking switchable the compound is able to take up cations after a photochemical trigger and exposure to acetonitrile gives back the open form.
In 1980 Yamashita et al.[12] construct a crown ether already incorporating the anthracene units (an anthracenophane) and also study ion uptake vs photochemistry.
Also in 1980 Shinkai throws out the anthracene unit as photoantenna in favor of an azobenzene moiety[13] and for the first time envisions the existence of molecules with an on-off switch.
In this system NMR spectroscopy shows that in the azo trans-form the polyether ring is free to rotate around its partner ring but then when a light trigger activates the cis azo form this rotation mode is stopped Kaifer and Stoddart in 1994 modify their molecular shuttle[19] such a way that an electron-poor tetracationic cyclophane bead now has a choice between two docking stations: one biphenol and one benzidine unit.
However, on addition of trifluoroacetic acid, the benzidine nitrogen atoms are protonated and the bead is fixed permanently on the biphenol station.
[20] The device consists of 400 bottom silicon nanowire electrodes (16 nanometer (nm) wide at 33 nm intervals) crossed by another 400 titanium top-nanowires with similar dimensions sandwiching a monolayer of a bistable rotaxane depicted below: Each bit in the device consists of a silicon and a titanium crossbar with around 100 rotaxane molecules filling in the space between them at perpendicular angles.