Boosting Ion Conductivities: Light-Modulated Azobenzene-Based Ionic Liquids in Vertical Nanochannels

Exploring stimuli-responsive ion-conductive materials is a challenging task, but it has gained increasing attention because of their enormous potential applications in actuators, sensors, and smart electronics. Here, we demonstrate a distinctive photoresponsive ion-conductive device that utilizes azobenzene-based ionic liquids ([AzoC n MIM][Br], where n = 2, 6, and 10), confined in nanochannels of anodic aluminum oxide (AAO) templates for photoisomerization. The structure of [AzoC n MIM][Br] comprises photoresponsive and hydrophobic azobenzene moieties, hydrophilic imidazolium cations, and negatively charged bromide ions. Therefore, [AzoC n MIM][Br] can form micelles and exhibit photoresponsive ion conductivities. The nanochannels of AAO templates exhibit a confinement effect on the formation of azobenzene-based ionic liquid micelles due to the pore size, thereby preventing the formation of larger micelles that could lead to a decrease in conductivity. Consequently, the ion conductivities of the azobenzene-based ionic liquids are higher in the nanochannels of the AAO templates. The effects of the length of carbon chains on the azobezene-based ionic liquids and the pore size of the AAO templates have also been investigated. Additionally, through irradiation with UV/vis light, [AzoC n MIM][Br] can undergo reversible isomerization, thereby reversibly changing the sizes of the micelles and subsequently altering the ion conductivities.