Threading-gated photochromism in [2]pseudorotaxanes.

Rigid, Y-shaped imidazole compounds containing the bis(thienyl)ethene moiety were designed and synthesized. The 4,5-bis(benzothienyl)-2-phenylimidazolium cations were then used as axles for [2]pseudorotaxane formation with 24-membered crown ether wheels. It was demonstrated using 1H NMR spectroscopy, UV-Vis absorption and emission spectroscopies that this host-guest interaction results in significant changes in the photochromic properties of the imidazolium axles. This is a rare example of gated photochromism, which exploits the recognition event of an interpenetrated molecular system to tune the photochromic properties in one of the components.