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.

The development of porous well-defined hybrid materials (e.g., metal-organic frameworks or MOFs) will add a new dimension to a wide number of applications ranging from supercapacitors and electrodes to "smart" membranes and thermoelectrics. From this perspective, the understanding and tailoring of the electronic properties of MOFs are key fundamental challenges that could unlock the full potential of these materials. In this work, we focused on the fundamental insights responsible for the electronic properties of three distinct classes of bimetallic systems, MM'-MOFs, MM'-MOFs, and M(ligand-M')-MOFs, in which the second metal (M') incorporation occurs through (i) metal (M) replacement in the framework nodes (type I), (ii) metal node extension (type II), and (iii) metal coordination to the organic ligand (type III), respectively. We employed microwave conductivity, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, pressed-pellet conductivity, and theoretical modeling to shed light on the key factors responsible for the tunability of MOF electronic structures. Experimental prescreening of MOFs was performed based on changes in the density of electronic states near the Fermi edge, which was used as a starting point for further selection of suitable MOFs. As a result, we demonstrated that the tailoring of MOF electronic properties could be performed as a function of metal node engineering, framework topology, and/or the presence of unsaturated metal sites while preserving framework porosity and structural integrity. These studies unveil the possible pathways for transforming the electronic properties of MOFs from insulating to semiconducting, as well as provide a blueprint for the development of hybrid porous materials with desirable electronic structures.

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.

This perspective focuses on the synthesis, characterization, and modeling of three classes of hierarchical materials with potential for sequestering radionuclides: nanoparticles, porous frameworks, and crystalline salt inclusion phases. The scientific impact of hierarchical structures and the development of the underlying crystal chemistry is discussed as laying the groundwork for the design, local structure control, and synthesis of new forms of matter with tailored properties. This requires development of the necessary scientific understanding of such complex structures through integrated synthesis, characterization, and modeling studies that can allow their purposeful creation and properties. The ultimate practical aim is to provide the means to create novel structure types that can simultaneously sequester multiple radionuclides. The result will lead to the creation of safe and efficient, long lasting waste forms for fission products and transuranic elements that are the products of nuclear materials processing waste streams. The generation of the scientific basis for working toward that goal is presented.

In this review, we highlight how recent advances in the field of actinide structural chemistry of metal-organic frameworks (MOFs) could be utilized towards investigations relative to efficient nuclear waste administration, driven by the interest towards development of novel actinide-containing architectures as well as concerns regarding environmental pollution and nuclear waste storage. We attempt to perform a comprehensive analysis of more than 100 crystal structures of the existing An (U,Th)-based MOFs to establish a correlation between structural density and wt% of actinide and bridge structural motifs common for natural minerals with ones typically observed in the solution chemistry of actinides. In addition to structural considerations, we showcase the benefits of MOF modularity and porosity towards the stepwise building of hierarchical material complexity and the capture of nuclear fission products, such as technetium and iodine. We expect that these facets not only contribute to the fundamental science of actinide chemistry, but also could foreshadow pathways for more efficient nuclear waste management.

Herein, we report the first example of ac rystalline metal-donor-fullerene framework, in which control of the donor-fullerene mutual orientation was achieved through chemical bond formation, in particular,bymetal coordination. The 13 Cc ross-polarization magic-angle spinning NMR spectroscopy, X-rayd iffraction, and time-resolved fluorescence spectroscopyw ere performed for comprehensive structural analysis and energy-transfer (ET) studies of the fulleretic donor-acceptor scaffold. Furthermore,i nc ombination with photoluminescence measurements,t he theoretical calculations of the spectral overlap function, Fçrster radius,e xcitation energies,a nd band structure were employed to elucidate the photophysical and ET processes in the prepared fulleretic material. We envision that the well-defined fulleretic donoracceptor materials could contribute not only to the basic science of fullerene chemistry but would also be used towards effective development of organic photovoltaics and molecular electronics.The success of fullerenes and their derivatives in engineering organic photovoltaics and molecular electronics is mainly owed to their electron-accepting properties and ultrafast electron/energy transfer. [1,2] As previously demonstrated, fullerene(acceptor)-donor alignment could significantly affect excitonic device performance.F or instance,t he arrangement of the donor fullerene is crucial for efficient energy/charge transfer, because of possible effects on the distance of exciton diffusion, p-p stacking, or Fçrster radius (resonance energy transfer). As ar esult, formation of fullerene stacks led to an enhancement of solar cell efficiency,in contrast to non-stacking fullerene derivatives. [3] There are few known reports of spatial organization of graphitic crystalline materials through the covalent linkage of fullerene derivatives. [4][5][6][7][8] Moreover,the known approaches for fulleretic material organization are mainly based on immobilization of the fullerenes inside porous matrices possessing alarge aperture. [9][10][11] There are very few reports of crystalline fullerene-metal-coordinated extended structures. [12][13][14][15] Furthermore,n one of these studies explore the concept demonstrated herein, which tackles the development of an ovel crystalline metal-donor-acceptor framework, in which control of the mutual orientation of the donor and fullerenebased acceptor was achieved through chemical bond formation, that is,m etal coordination. Despite the tremendous interest in self-assemblies (in particular,c oordination polymers such as covalent or metal-organic frameworks;COFs or MOFs) [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and fullerene chemistry,t ot he best of our knowledge the prepared metal-organic fullerene-containing framework is the first example of ac rystalline hybridextended structure,inw hich control over mutual orientation of both donor and fullerene-based acceptor is achieved through metal coordination (Scheme 1). Scheme 1. As chematic representation of organizatio...