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.
Thermodynamic studies of actinide-containing metal−organic frameworks (An-MOFs), reported herein for the first time, are a step toward addressing challenges related to effective nuclear waste administration. In addition to An-MOF thermochemistry, enthalpies of formation were determined for the organic linkers, 2,2′-dimethylbiphenyl-4,4′-dicarboxylic acid (H 2 Me 2 BPDC) and biphenyl-4,4′-dicarboxylic acid (H 2 BPDC), which are commonly used building blocks for MOF preparation. The electronic structure of the first example of An-MOF with mixed-metal AnAn′-nodes was influenced through coordination of transition metals as shown by the density of states near the Fermi edge, changes in the Tauc plot, conductivity measurements, and theoretical calculations. The "structural memory" effect (i.e., solvent-directed crystalline−amorphous−crystalline structural dynamism) was demonstrated as a function of node coordination degree, which is the number of organic linkers per metal node. Remarkable three-month water stability was reported for Th-containing frameworks herein, and the mechanism is also considered for improvement of the behavior of a U-based framework in water. Mechanistic aspects of capping linker installation were highlighted through crystallographic characterization of the intermediate, and theoretical calculations of free energies of formation (ΔG f ) for U-and Th-MOFs with 10-and 12-coordinated secondary building units (SBUs) were performed to elucidate experimentally observed transformations during the installation processes. Overall, these results are the first thermochemical, electronic, and mechanistic insights for a relatively young class of actinide-containing frameworks.
This review applies a holistic approach for recognizing a pattern in the photophysics–structure relationship of chromophore in porous crystalline matrices.
Acquiring fundamental knowledge of properties of actinide‐based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics–electronics correlation for actinide‐containing metal‐organic frameworks (An‐MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide‐based heterometallic MOFs through integration of photochromic linkers. Optical cycling, modeling of density of states near the Fermi edge, conductivity measurements, and photoisomerization kinetics were employed to shed light on the process of tailoring optoelectronic properties of An‐MOFs. Furthermore, the first photochromic MOF‐based field‐effect transistor, in which the field‐effect response could be changed through light exposure, was constructed. As a demonstration, the change in current upon light exposure was sufficient to operate a two‐LED fail‐safe indicator circuit.
In this Perspective, we highlight how recent studies of heterometallic metal–organic frameworks (MOFs) could lead to advances to the energy landscape. The ability to merge the inherent properties of MOFs, including their modularity, porosity, versatility, high surface area, and structural tunability, with the ability to engineer metal nodes could benefit both the classical realm of MOF applications as well as the recent shift toward electronic structure studies. This Perspective is intended to provide a glimpse into the advances, challenges, and future pathways for the uses of heterometallic MOFs in sectors ranging from the oxygen evolution reaction to nuclear waste administration in order to ultimately provide valuable potential materials to the ever-expanding technological landscape.
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