In this review, we highlight how recent advances achieved in the fields of photochemistry and photophysics of metal-organic frameworks (MOFs) could be applied towards the engineering of next generation MOF-based sensing devices. In addition to high surface area and structural tunability, which are crucial for efficient sensor development, progress in the field of MOF-based sensors could rely on the combination of MOF light-harvesting ability, understanding energy transfer processes within a framework, and application of MOF-based photocatalysis towards sensing enhancement. All photophysical concepts could be integrated within one material to improve efficiency and selectivity of sensing devices. Thus, the focus of this review is shifted towards a "beyond the pores" approach, which could foreshadow new guidelines for sensor engineering.

In this Review, we showcase the upsurge in the development and fundamental photophysical studies of more than 100 metal−organic frameworks (MOFs) as versatile stimuli-responsive platforms. The goal is to provide a comprehensive analysis of the field of photoresponsive MOFs while delving into the underlying photophysical properties of various classes of photochromic molecules including diarylethene, azobenzene, and spiropyran as well as naphthalenediimide and viologen derivatives integrated inside a MOF matrix as part of a framework backbone, as a ligand side group, or as a guest. In particular, the geometrical constraints, photoisomerization rates, and electronic structures of photochromic molecules integrated inside a rigid MOF scaffold are discussed. Thus, this Review reflects on the challenges and opportunities of using photoswitchable MOFs in next-generation multifunctional stimuli-responsive materials while highlighting their use in optoelectronics, erasable inks, or as the next generation of sensing devices. CONTENTS1. Introduction 8790 2. Photoresponsive Moieties as a Framework Backbone 8791 2.1. Diarylethene Derivatives as a Framework Backbone 8797 2.2. Viologen Derivatives as a Framework Backbone 8799 2.3. Naphthalenediimide Derivatives as a Framework Backbone 8801 3. Photoresponsive Moiety as a Ligand Side Group 8801 3.1. Azobenzene Moiety as a Linker Side Group 8801 3.2. Diarylethene Moiety as a Linker Side Group 8803 3.3. Spiropyran Moiety as a Linker Side Group 8803 3.4. Viologen Moiety as a Linker Side Group 8804 4. Photochromic Compound as a Guest 8804 4.1. Azobenzene as a Guest 8804 4.2. Diarylethene as a Guest 8805 4.3. Spiropyran as a Guest 8805 4.4. Viologen as a Guest 8805 4.5.

Stimuli-responsive materials are vital for addressing emerging demands in the advanced technology sector as well as current industrial challenges. Here, we report for the first time that coordinative integration of photoresponsive building blocks possessing photochromic spiropyran and diarylethene moieties within a rigid scaffold of metal-organic frameworks (MOFs) could control photophysics, in particular, cycloreversion kinetics, with a level of control that is not accessible in the solid state or solution. On the series of photoactive materials, we demonstrated for the first time that photoisomerization rates of photochromic compounds could be tuned within almost 2 orders of magnitude. Moreover, cycloreversion rates of photoresponsive derivatives could be modulated as a function of the framework structure. Furthermore, through MOF engineering we were able to achieve complete isomerization for coordinatively immobilized spiropyran derivatives, typically exhibiting limited photoswitching behavior in the solid state. For instance, spectroscopic analysis revealed that the novel monosubstituted spiropyran derivative grafted to the backbone of the MOF pillar exhibits a remarkable photoisomerization rate of 0.16 s, typical for cycloreversion in solution. We also applied the acquired fundamental principles toward mapping of changes in material properties, which could provide a pathway for monitoring material aging or structural deterioration.

Electronic structure modulation of metal–organic frameworks (MOFs) through the connection of linker “wires” as a function of an external stimulus is reported for the first time. The established correlation between MOF electronic properties and photoisomerization kinetics as well as changes in an absorption profile is unprecedented for extended well-defined structures containing coordinatively integrated photoresponsive linkers. The presented studies were carried out on both single crystal and bulk powder with preservation of framework integrity. An LED-containing electric circuit, in which the switching behavior was driven by the changes in MOF electronic profile, was built for visualization of experimental findings. The demonstrated concept could be used as a blueprint for development of stimuli-responsive materials with dynamically controlled electronic behavior.

Growing necessity for efficient nuclear waste management is a driving force for development of alternative architectures toward fundamental understanding of mechanisms involved in actinide (An) integration inside extended structures. In this manuscript, metal-organic frameworks (MOFs) were investigated as a model system for engineering radionuclide containing materials through utilization of unprecedented MOF modularity, which cannot be replicated in any other type of materials. Through the implementation of recent synthetic advances in the MOF field, hierarchical complexity of An-materials was built stepwise, which was only feasible due to preparation of the first examples of actinide-based frameworks with "unsaturated" metal nodes. The first successful attempts of solid-state metathesis and metal node extension in An-MOFs are reported, and the results of the former approach revealed drastic differences in chemical behavior of extended structures versus molecular species. Successful utilization of MOF modularity also allowed us to structurally characterize the first example of bimetallic An-An nodes. To the best of our knowledge, through combination of solid-state metathesis, guest incorporation, and capping linker installation, we were able to achieve the highest Th wt % in mono- and biactinide frameworks with minimal structural density. Overall, the combination of a multistep synthetic approach with homogeneous actinide distribution and moderate solvothermal conditions could make MOFs an exceptionally powerful tool to address fundamental questions responsible for chemical behavior of An-based extended structures and, therefore, shed light on possible optimization of nuclear waste administration.