Efficient Gating of Ion Transport in Three-Dimensional Metal-Organic Framework Sub-Nanochannels with Confined Light-Responsive Azobenzene Molecules.

One-dimensional (1D) nanochannels modified with responsive molecules have been fabricated to replicate gating functionalities of biological ion channels. But gating effects of the small-molecular-modified nanochannels are usually weak mainly because small molecular gates could not efficiently block the large channels at the close states. Herein we report three-dimensional (3D) metal-organic-framework (MOF) sub-nanochannels (SNCs) confined with azobenzene (AZO) molecules to achieve efficient light-gating functionalities. The 3D MOFSNCs consisting of ~9-12-A-sized cavities connected by ~6-A-sized triangular windows work as angstrom-scale ion channels, while confined AZO within the MOF cavities function as light-driven molecular gates to efficiently regulate the ion flux. The AZO-MOFSNCs show a good cyclic gating performance and high on-off ratios up to ~17.8, which is one order of magnitude higher than ratios of ~1.3-1.5 observed in conventional 1D AZO-modified nanochannels. This work provides a new and feasible strategy to develop highly-efficient switchable ion channels based on 3D porous MOFs and small responsive molecules.