The progress of electrochromic materials based on metal–organic frameworks

Electrochromic (EC) materials can reversibly transform their optical properties, including the transmittance, reflectance, absorptance, and color, under an external voltage bias, showing lot of potential for applications in smart devices. Metal-organic frameworks (MOFs) are organic–inorganic hybrid porous materials composed of metal centers and organic linkers through coordination bonds. Considering the unlimited possibility of inorganic and organic components, large specific surface area, unique permanent porosity, facile structural and surface properties, MOFs have the characteristics of organic–inorganic hybridization and rich nanoporous structure, which inherently meets the requirements for improving the performance of EC materials, and is expected to become a new generation of excellent EC materials. In this review, the electrical conductivity of MOFs and ion diffusion in MOFs are briefly introduced. The latest advances in MOFs-based EC materials are then systematically summarized, including four types: MOFs with redox active linkers, MOFs with redox active metal centers, MOFs with entrapped redox active guest molecules in their pores or channels, and MOF derivatives. The MOF-based multifunctional EC devices are also briefly reviewed. This review could encourage more researchers to enrich the MOF-based EC materials to fully release the application potential of MOFs as EC materials, and provide assistance for the future smart devices.