Photoresponsive Ionic Liquids with an Azobenzene Moiety

We examined photoresponsive ionic liquids containing an azobenzene moiety. Ionic liquids with a p,p′-azobenzene or o,p′-tetrafluoroazobenzene moiety exhibit a reversible solid-to-liquid phase transition induced by photo- and thermal-stimulation. o,p′-Azobenzene, which exists as an ionic liquid with a bent structure, is in a liquid state even as a trans-isomer. Such photoresponsive ionic liquids may be useful as novel functional materials, such as in optical sensors.