Photoswitchable Nanoporous Metal–Organic Framework Monolayer Film for Light-Gated Ion Nanochannel

Two-dimensional metal–organic framework (MOF) monolayer films, which can be considered as large-area, periodically ordered thin films with atom- or single-unit thickness, have attracted extensive attention due to their special properties and wide range of potential applications. However, the preparation of MOF monolayer films is still a great challenge, and the introduction of functional groups into MOF monolayer films is seldom reported. Here, we report the first centimeter-scale, photo-switchable, free-standing MOF monolayer film formed by self-assembly of poly­(methyl methacrylate-co-acrylamidoazobenzene)-coated MOF nanoparticles at the water–air interface. This self-assembled MOF monolayer film is extremely thin (∼220 or 50 nm) and has a high MOF loading (85 wt %), while exhibiting remarkable reversible photoswitching properties under alternating exposure to 365 nm UV and white light. Inspired by this, a light-gated ion nanochannel device is fabricated, which enables reversible ″OFF–ON″ changes of the ionic flux and has promising applications in the field of photoelectric conversion. This provides a modular route to design large-area, free-standing functional MOF monolayer films.