Switchable Ionic Transportation in the Nanochannels of the MOFs Triggered by Light and pH

The construction of a biomimetic ionic channel is of great significance for the fabrication of smart biodevices or logic circuit. Inspired by the selective permeability of the cell membrane toward bioions, a light-induced and pH-modulated artificial nanochannel is herein prepared by integrating the multistimuli-response molecule of carboxylated spiropyran (SP-COOH) into the frameworks of NU-1000 (Zr-based MOFs defined by Northwestern University). The loading density of the SP-COOH could reach as high as 7 wt % while keeping unchanged crystallinity and high porosity. Thanks to the precise matching of pore size of NU-1000 and molecular dimensions of SP-COOH, the loaded molecules could proceed free and reversible for isomerization between the hydrophilic and hydrophobic states. The ion-switchable characteristics of the channel are implemented by the amphiphilic change of the light-controlled gate molecule. Additionally, in the hydrophilic state, the channel presents reversible affinity toward cations or anions due to the reverse charge state induced by pH, thus constructing a pH-controlled subgate. Taking [Ru(NH₃)₆]³⁺ and [Fe(NH₃)]^3- as the model cation and anion, their redox peak currents occur as reversible change under different signal combinations of light and pH. Moreover, in accordance with the ionic selective permeability, several logic circuits/devices are designed to display the relationships between exogenous stimuli and ionic transportations in a computer language, prefiguring their wide application prospects in electronic devices and life sciences.