Functional Guest in Metal‐Organic Frameworks^†

Comprehensive Summary Metal‐organic frameworks (MOFs) contain ordered metal nodes, organic linkers, and guest species, which generally determine their properties respectively and/or synergistically. Guest species play a crucial role in maintaining charge balance and structural stability of MOFs. In addition to metal nodes and organic linkers, the type and distribution of guests can significantly influence the properties of MOFs, such as optics, magnetism, chirality, and catalysis. Understanding the role of guests to the properties of MOFs remains great challenge due to the complex chemical and electronic structures of MOFs. Recently, progresses on guest‐dependent properties of MOFs have been reported, which not only advanced our knowledge of host‐guest interactions and energy transfer mechanisms but also led to intriguing applications such as luminescent sensors, tunable magnetic materials, enantioselective materials, and catalysts. Crucially, the interactions between the host and guest can be finely tuned by altering the type and amount of guests without changing the core framework, allowing for precise regulation of targeted properties. In this review, we will explore how guest‐induced variations impact the optic, magnetic, chiral, and catalytic properties of MOFs, followed by an examination of the synergistic effects between hosts and guests, which is highly important for the development of advanced functional materials. Key Scientists Plenty of outstanding scientists have reported a great number of MOFs with their interesting properties. Diverse regulation and modification strategies have been developed towards the metal centers, the organic linkers, and the functional guests according to the binding modes and host‐guest interactions, to bring or enhance certain properties of MOFs. Guests in the pores of MOFs are crucial part for their properties based on the guest‐induced properties or the synergistic effects between the hosts and guests, which has been greatly developed by their continuous industrious works. Stories to be Continued …