Search

Engineering coordinated rotational motion in porous architectures enables the fabrication of molecular machines in solids. A flexible two-fold interpenetrated pillared Metal-Organic Framework precisely organizes fast mobile elements such as bicyclopentane (BCP) (107 Hz regime at 85 K), two distinct pyridyl rotors and E-azo group involved in pedal-like motion. Reciprocal sliding of the two sub-networks, switched by chemical stimuli, modulated the sizes of the channels and finally the overall dynamical machinery. Actually, iodine-vapor adsorption drives a dramatic structural rearrangement, displacing the two distinct subnets in a concerted piston-like motion. Unconventionally, BCP mobility increases, exploring ultra-fast dynamics (107 Hz) at temperatures as low as 44 K, while the pyridyl rotors diverge into a faster and slower dynamical regime by symmetry lowering. Indeed, one pillar ring gained greater rotary freedom as carried by the azo-group in a crank-like motion. A peculiar behavior was stimulated by pressurized CO2, which regulates BCP dynamics upon incremental site occupation. The rotary dynamics is intrinsically coupled to the framework flexibility as demonstrated by complementary experimental evidence (multinuclear solid-state NMR down to very low temperatures, synchrotron radiation XRD, gas sorption) and computational modelling, which helps elucidate the highly sophisticated rotor-structure interplay.

Stimuli-responsive molecular systems support within permanently porous materials offer the opportunity to host dynamic functions in multifunctional smart materials. However, the construction of highly porous frameworks featuring external-stimuli responsiveness, for example by light excitation, is still in its infancy. Here a general strategy is presented to construct spiropyran-functionalized highly porous switchable aromatic frameworks by modular and high-precision anchoring of molecular hooks and an innovative in situ solid-state grafting approach. Three spiropyran-grafted frameworks bearing distinct functional groups exhibiting various stimuli-responsiveness are generated by two-step post-solid-state synthesis of a parent indole-based material. The quantitative transformation and preservation of high porosity are demonstrated by spectroscopic and gas adsorption techniques. For the first time, a highly efficient strategy is provided to construct multi-stimuli-responsive, yet structurally robust, spiropyran materials with high pore capacity which is proved essential for the reversible and quantitative isomerization in the bulk as demonstrated by solid-state NMR spectroscopy. The overall strategy allows to construct dynamic materials that undergoes reversible transformation of spiropyran to zwitterionic merocyanine, by chemical and physical stimulation, showing potential for pH active control, responsive gas uptake and release, contaminant removal, and water harvesting.A post-synthetic strategy for the construction of highly porous aromatic frameworks is presented. This approach enables the fabrication of a series of materials with a wide range of properties and applicability in diverse fields.image

The integration of photoswitchable elements into porous solids provides fascinating opportunities to modulate material properties. However, the fabrication strategies of these materials are dedicated only to preserving the function of the photoswitches in the solid while introducing new properties beyond those offered by the individual components remains challenging. Here, we present a three-state porous aromatic framework constructed from a bistable overcrowded alkene-based photoswitch. The framework was fabricated using a Yamamoto coupling polymerization of an engineered hexadentate monomer to yield swellable and hierarchical microporous/mesoporous architectures with densely integrated photoswitches. The interplay of hierarchical porosity, flexible backbone, and reversible photoisomerization between two isomers generates three unique and distinct porosity states that can be accessed in sequence upon application of external stimuli to induce sponge-like behavior. This material represents a major step toward light-responsive materials capable of harnessing limited molecular-scale motion and converting it into an on-demand response over hierarchical length scales toward a practical output.

Homogenous radioactive gas contamination constitutes the hardest challenge for radioprotection due to its elusive nature. Most common radioactive gas are 85Kr, 222Rn, and tritiated (3H) vapors. Each of them has different challenges, often leading to specialized single-gas detectors. The state-of-the-art detection either produces chemical-radiological waste, is hard to implement online, or requires large volume. A new paradigm is presented for radioactive gas detection that can perform online detection on any gas and fit in the hand. This study use photoluminescent metal organic frameworks (MOFs) as both porous gas sponges and scintillators. The response of several zinc based MOF is studied, using a unique radioactive gas test bench. These tests showed that MOFs are able to both concentrate and detect successfully 85Kr. The investigation is completed with calibration with different activities. The study also reports detection of 222Rn, and measurement of its half-life. Finally, the study is completed with the successful detection of tritiated dihydrogen, commonly known to be a hard radionuclide to detect due to its low energy and penetration range. This paper shows that scintillating MOFs are a powerful solid-state approach and a practical solution to the challenge of radioactive gas measurements.

The assembly by design of suitable molecular building blocks produces Metal-Organic Frameworks (MOFs) and Porous Organic Polymers (POPs) architectures endowed with high free volume and large accessible surface area. The rich and versatile chemistry of the building blocks and the strict control over framework topology and pore geometry boost the development of tailored materials for selective gas sorption and release, fabrication of molecular rotors and photonic applications.

Suitably functionalized porous matrices represent versatile platforms to support well-dispersed catalytic centers. In the present study, porous organic polymers (POPs) containing phosphine oxide groups were fabricated to bind transition metals and to be investigated for potential electrocatalytic applications. Cross-linking of mono- and di-phosphine monomers with multiple phenyl substituents was subject to the Friedel-Crafts (F-C) reaction and the oxidation process, which generated phosphine oxide porous polymers with pore capacity up to 0.92 cm3/g and a surface area of about 990 m2/g. The formation of the R3P·BH3 borohydride adduct during synthesis allows to extend the library of phosphine-based monomeric entities when using FeCl3. The porous polymers were loaded with 0.8-4.2 w/w % of cobalt(II) and behaved as hydrogen evolution reaction (HER) catalysts with a Faradaic efficiency of up to 95% (5.81 × 10-5 mol H2 per 11.76 C) and a stable current density during repeated controlled potential experiments (CPE), even though with high overpotentials (0.53-0.68 V to reach a current density of 1 mA·cm-2). These studies open the way to the effectiveness of tailored phosphine oxide POPs produced through an inexpensive and ecofriendly iron-based catalyst and for the insertion of transition metals in a porous architecture, enabling electrochemically driven activation of small molecules.

Molecular rotors offer a platform to realize controlled dynamics and modulate the functions of solids. The motional mechanisms in arrays of rotors have not been explored in depth. Crystal-like porous organosilicas, comprising p-phenylene rotators pivoted onto a siloxane scaffold, were modelled using molecular dynamics (MD) simulations. Long simulations, on a microsecond scale, allowed to follow the reorientation statistics of rotor collections and single out group configurations and frequency distributions as a function of temperature. The motions observed in the MD simulations support a multiple-site model for rotor reorientations. Computed motional frequencies revealed a complex rotatory phenomenon combining an ultra-fast libration motion (oscillation up to 30°) with a slow and fast 180° flip reorientation. Adopting a multiple-site model provides a more accurate simulation of the 2H-NMR spectra and a rationalization of their temperature dependence. In particular, rotators endowed with distinct rates could be explained by the presence of slower rings locked in a T-shaped conformation.

The design of solid materials comprising rotors that can convert external stimuli into actions is growing exponentially. [1] In particular, the incorporation of fast-reorientating dipoles onto molecular rotors is very attractive for the fabrication of materials responsive to oscillating or static electric fields. In this work, we successfully synthetized two new isostructural aluminum-based metal-organic frameworks (MOFs), endowing bicyclopentanedicarboxylate molecular rotors as linkers, denominated frustrated trigonal rotors (FTR), in the hydrogenated and partly fluorinated derivatives (FTR-F2). [2] Multi-nuclear high-resolution ssNMR techniques were used to characterize the new crystal structures, demonstrating the purity and symmetry of the materials. The empty space that surrounds the rotors allowing them to move freely was directly probed with continuous-flow hyperpolarized (HP) 129Xe NMR. The observed chemical shift anisotropy (see Fig. 1 Left) indicates that the xenon is exploring an ellipsoidal cross-section, as observed in the rhombohedral structure of the framework. 1H T1 relaxation times were collected down to 2 K (see Fig.1, Right) in order to understand the motional behavior of the molecular rotors having CF2 groups mounted, which were proved hyper-mobile even at such low temperatures with extremely low activation energies for dipole reorientation. In particular, the T1 revealed multiple relaxation phenomena due to correlated dipole-rotor configurations. The discovery paved the way for the realization of dipolar rotors unaffected by thermal noise to be used in molecular machines with low energy dissipation and controllable dynamics.

Detecting radioactive gases is becoming essential in modern society to monitor nuclear activity and reduce the exposure risk to those gases being potentially harmful to persons and the environment. Liquid scintillators, i.e., materials that produce light pulses upon interaction with ionizing radiation, are currently used as radiation detectors despite the low sensitivity, complex sampling and preparation procedure. A potential breakthrough solution to overcome these problems is using solid porous scintillators that concentrate the gas and increase the detection sensitivity. Metal-organic frameworks (MOFs) stand out as materials of choice for this application being highly porous and having rigid and directional connectivity that allows the inclusion of highly luminescent conjugated chromophores. The excellent scintillating properties of MOFs have already been demonstrated by previous works, where the fluorescent MOFs were embedded in a polymer generating a composite material.[1,2] Here we demonstrate the capability of a novel porous hafnium-based MOF exploiting dicarboxy-9,10-diphenylanthracene (DPA) as a scintillating conjugated ligand to detect gaseous radionuclides.[3] The nanocrystals (Fig. 1A) show fast scintillation properties in the nanosecond time range and a fluorescent quantum yield of about 40%. The presence of a heavy element such as hafnium (Hf) also enables a good light intensity output under ionizing radiation. The MOF’s highly accessible porosity allows it to host noble gas atoms (Fig. 1B) that can diffuse inside the cavities, as proved by argon (Ar) and krypton (Kr) adsorption isotherms at 77 K (Fig. 1C). Direct detection of noble gas diffusion into the pores have been observed by hyperpolarized (HP) 129Xe NMR experiments (Fig. 1D), demonstrating the highly selective uptake of Xe in extremely diluted conditions (2% Xe in N2 and He gas mixture) under flow conditions. Finally, adsorption and detection of radionuclides have been explored using a newly d

Rotors, motors and switches in the solid state find a favorable playground in Metal Organic Frameworks (MOFs), thanks to their large free volume, which allows for fast dynamics. We have realized a fast molecular rotor in a Zn-MOF whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures (2 K) [1,2]. Geared molecular rotors with negligible energy-requirements in pillared MOFs enabled fast yet controllable and correlated rotary motion [3], showing an unprecedented cascade mechanism. Chemical stimuli such as the use of CO2 diffused through the open pores changed dramatically the global rotation mechanism and rotor speed. Attractive functional properties, such as dielectric, optical and ferroelectric switchable properties, can be activated by incorporating fast-reorientable dipoles onto molecular rotors to produce materials responsive to static or oscillating electric fields. In fluorinated MOFs comprising a wheel-shaped ligand with geminal rotating fluorine atoms, we tailored benchmark dipole rotational dynamics in the presence of a concerted dance of dipoles with practically null activation energy of 17 cal mol-1[4]. Furthermore, motors were inserted into MOFs wherein two distinct linkers with complementary light absorption-emission properties were integrated into the same material. Unidirectional motion was achieved by exposure to sunlight of the solid material, which thus behaves as an autonomous nanodevice [5]. We demonstrated that fluorescent metal–organic framework (MOF) nanocrystals can work as fast scintillators [6]. The MOF comprised high-Z linking nodes that interact with the ionizing radiation and are arranged in an orderly fashion at a nanometric distance from ligand emitters. Their incorporation in the framework enabled fast sensitization of the ligand fluorescence, showing an ultrafast scintillation rise time of ~50 ps. Additionally, two ligands of equal molecular length and connectivity, yet complement

Molecular rotors, motors and photo-switches in the solid state find a favourable playground in nanoporous materials, such as MOFs and POPs, thanks to their large free volume. In this field a particularly prominent application of solid state NMR is the study of dynamic processes in solids and in the gas phase. We have realized a ultra-fast molecular rotor based on bicyclo[1.1.1]pentane–dicarboxylate moiety, assembled in a cubic Zn-MOF structure. The rotors experience fast molecular reorientation even at temperature below 2 K, with a negligible activation barrier as low as 6 cal mol-1, resulting from the symmetry mismatch between the tri-fold geometry of the rotor and the four-fold symmetry imposed by the frameworks [1]. Two distinct ultrafast and interacting molecular rotors can be arranged in pillar-and-layer 3D arrays MOF, wherein the rotors undergo sequential motional behaviour activated at distinct temperatures, as supported by 2H solid-echo, T1(1H) relaxation NMR and DFT modelling [2]. Attractive functional properties, such as dielectric switchable property, can be activated by incorporating fast-reorientable dipoles onto molecular rotors. Fluorinated Al-MOFs, comprising a wheel-shaped ligand with geminal rotating fluorine atoms, produced a benchmark dynamics of correlated dipolar rotors. Gas accessibility, shown by hyperpolarized 129Xe NMR, allowed for chemical stimuli intervention: CO2 triggered dipole reorientation, reducing their collective dynamics and stimulating a dipole configuration change in the crystal [3]. CO2 diffusion in a porous crystalline material, in which the channels are decorated by double helices of electrostatic charges, has been described by 2D 1H-13C HETCOR MAS NMR experiments and by anisotropic line-shape analysis of 13C, providing peculiar details about the role of electrostatic interactions in gas transport phenomena [4]. Moreover, the insertion of photo-responsive molecular motors with active dynamical behavior allowed the generation

Solid-state NMR (ssNMR) is a unique tool for characterising Metal-Organic Frameworks (MOFs), a new and emerging class of porous hybrid crystalline materials. While the crystal structures are usually determined by diffraction techniques, ssNMR can give a comprehensive insight into the dynamic of the molecular moieties comprising the material and the gases diffusing inside the pores. Multi-nuclear and multi-dimensional high- resolution ssNMR techniques are used to demonstrate structural purity, activation completeness and structural changes in the material. 1H and 13C T1 spin-lattice relaxation times collected at variable temperatures provide information regarding the motional behaviour of the molecular moieties, elucidating the presence of molecular rotors and their related activation energies. It is also possible to study the interaction between the framework and adsorbed guests by sealing the NMR rotors under the desired conditions, for example, in the presence of vapours or under gas pressure, and monitor the consequent variation in the mobility of the molecular rotors. This is of particular interest for studying flexible crystalline materials that undergo structural changes depending on the adsorbed guest. Finally, the permanent porosity of the MOFs can be studied by hyperpolarised (HP) 129Xenon NMR. This laser-assisted technique exploits 129Xe nuclei as a probe to explore the shape and size of the cavities in the porous materials. Due to the high sensitivity of the HP 129Xe nuclei, it is possible to work in extremely diluted conditions (2% Xe in He/N2 gas mixture) to prevent room temperature Xe-Xe interactions and under flow conditions, thus proving direct accessibility of the pores and preferential sites of the framework. [1] Perego et al. Angew. Chem. Int. Ed. 2023, 62, e202215893 [2] Orfano et al. Nature Photonics 2023, DOI: 10.1038/s41566-023-01211-2 [2] Sozzani et al. Hyperpolarised Xenon-129 Magnetic Resonance: Concepts, Production, Techniques and Applicat

Fluorinated Metal-Organic Frameworks (MOFs), comprising a wheel-shaped ligand with geminal rotating fluorine atoms, produced benchmark mobility of correlated dipolar rotors at 2 K, with practically null activation energy (Ea=17 cal mol−1). 1H T1 NMR revealed multiple relaxation phenomena due to the exchange among correlated dipole-rotor configurations. Synchrotron radiation X-ray diffraction at 4 K, Density Functional Theory, Molecular Dynamics and phonon calculations showed the fluid landscape and pointed out a cascade mechanism converting dipole configurations into each other. Gas accessibility, shown by hyperpolarized-Xe NMR, allowed for chemical stimuli intervention: CO2 triggered dipole reorientation, reducing their collective dynamics and stimulating a dipole configuration change in the crystal. Dynamic materials under limited thermal noise and high responsiveness enable the fabrication of molecular machines with low energy dissipation and controllable dynamics.

Natural and anthropogenic gas radionuclides such as radon, xenon, hydrogen and krypton isotopes must be monitored to be managed as pathogenic agents, radioactive diagnostic agents or nuclear activity indicators. State-of-the-art detectors based on liquid scintillators suffer from laborious preparation and limited solubility for gases, which affect the accuracy of the measurements. The actual challenge is to find solid scintillating materials simultaneously capable of concentrating radioactive gases and efficiently producing visible light revealed with high sensitivity. The high porosity, combined with the use of scintillating building blocks in metal–organic frameworks (MOFs), offers the possibility to satisfy these requisites. We demonstrate the capability of a hafnium-based MOF incorporating dicarboxy-9,10-diphenylanthracene as a scintillating conjugated ligand to detect gas radionuclides. Metal–organic frameworks show fast scintillation, a fluorescence yield of ∼40%, and accessible porosity suitable for hosting noble gas atoms and ions. Adsorption and detection of 85Kr, 222Rn and 3H radionuclides are explored through a newly developed device that is based on a time coincidence technique. Metal–organic framework crystalline powder demonstrated an improved sensitivity, showing a linear response down to a radioactivity value below 1 kBq m−3 for 85Kr, which outperforms commercial devices. These results support the possible use of scintillating porous MOFs to fabricate sensitive detectors of natural and anthropogenic radionuclides.

The precise spatial assembly of chromophores inside MOF allows for the rational fabrication of photonic materials with unique photophysical properties. We propose an innovative radioactive gas detector based on highly porous luminescent MOFs.[1] Hf-based MOFs containing diphenyl anthracene (DPA) moieties display high porosity (SBET = 2550 m2 g-1), fast and reversible adsorption of noble gases (proven by combined experimental adsorption and simulation methods) and high photoluminescence and scintillating properties. After exposure to radioactive gases, Hf-DPA displays fast and bright scintillation sensitized by the decay of the radioactive nuclei that allows for their effective detection at ultra-low concentrations. Indeed, 85Kr isotope was detected even at activity as low as 0.3 kBq⋅m3, below the minimum value declared for commercial devices, strongly supporting the development of MOFbased scintillators for radioactive gas detection. Fast composite scintillators were engineered by embedding nanocrystalline Zr-MOFs containing highly luminescent DPA moieties in a continuous polymer matrix.[2] The hybrid bulk scintillators display good light yield, fast time response and an ultrafast scintillation rise time of ~ 50 ps, making them promising materials for time resolved applications. Moreover, nanocrystalline hetero-ligand Zr-based MOFs with high luminescent quantum yield and large Stokes shift emission were engineered by coassembly donor and acceptor chromophores, diphenyl anthracene (DPA) and diphenyl tetracene (DPT) moieties, respectively, to generate reabsorption-free emitters with potential applications in bioimaging, solar luminescent concentrators and bulk scintillators.[3] The two luminescent ligands, with similar molecular length and topology, were homogeneously inserted inside the MOF nanocrystals as proven by 129Xe hyperpolarized NMR experiments. The overlap between the emission frequency of DPA molecule and the absorption spectrum of DPT, and the precise spat

The modular and isoreticular nature of metal-organic frameworks (MOFs) permits the exploration of structural frameworks that allow for control over the ligand environment. This allows for tuning the ligand’s interactions with neighbouring moieties within the MOF. Conventionally molecular rotors used as struts in MOFs are isolated to reduce or eliminate interactions with their environment towards achieving fast rotary dynamics. Inserting bicyclo[1.1.1]pentandioate (FTR) rotors into a cubic framework yielded isolated rotors with an energy barrier for rotation of a couple of calories per mole (Fig 1 A).[1] The outstanding synthetic versatility of MOFs allows us to insert the FTR rotors into a pillar-and-layer Zn-MOF and a geminal fluorinated FTR rotor into an Al-MOF where the rotors can interact with their neighbours. Contrary to expectations, these rotors navigate the rotational potential energy landscape in such a way as to produce co-rotating pairs of rotors or geared molecular rotors. These geared molecular rotors have very low energy barriers for rotation (24 cal/mol) owing to the synchroneity of their rotation.[2] Additionally, the dipolar FTR-F2 rotor in the Al-MOF forms layers of interacting rotors oriented in different configurations. Interconversion between the different rotor configurations is achieved by the highly dynamic cooperative reorientation cascade of the dipolar rotors with a very low barrier for reorientation of ca. 17 cal/mol (Fig 1 B). [3] References [1] J. Perego, S. Bracco, M. Negroni, C. X. Bezuidenhout, G. Prando, P. Carretta, A. Comotti, P. Sozzani Nature Chem. 2020, 12, 845. [2] J.Perego, C. X. Bezuidenhout, S. Bracco, G. Prando, L. Marchiò, M. Negroni, P. Carretta, P. Sozzani, and A. Comotti JACS 2021 143 (33), 13082-13090. [3] Perego, J.; Bezuidenhout, C. X.; Bracco, S.; Piva, S.; Prando, G.; Aloisi, C.; Carretta, P.; Kaleta, J.; Le, T. P.; Sozzani, P.; Daolio, A.; Comotti, A., Angew. Chem. Int. Ed 2023, 62, e202215893.

Rotors, motors and switches in the solid state find a favorable playground in in Metal Organic Frameworks (MOFs), thanks to their large free volume, which allows for fast dynamics. We have realized a fast molecular rotor in a Zn-MOF whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures (2 K) [1,2]. Geared molecular rotors with negligible energy-requirements in pillared MOFs enabled fast yet controllable and correlated rotary motion[3], showing an unprecedented cascade mechanism. Chemical stimuli such as the use of CO2 diffused through the open pores changed dramatically the global rotation mechanism and rotor speed. Attractive functional properties, such as dielectric, optical and ferroelectric switchable properties, can be activated by incorporating fast-reorientable dipoles onto molecular rotors to produce materials responsive to static or oscillating electric fields. In fluorinated MOFs comprising a wheel-shaped ligand with geminal rotating fluorine atoms, we tailored benchmark dipole rotational dynamics even in the presence of cooperative motion with practically null activation energy of 17 cal mol-1. The mobility in the fluorinated MOF, especially in the 2–10 K temperature range, is due to the presence of a concerted dance of dipoles triggered by the interactions among nearest-neighbour rotors[4]. Furthermore, motors were inserted into MOFs wherein two distinct linkers with complementary light absorption-emission properties were integrated into the same material. Unidirectional motion was achieved by exposure to sunlight of the solid material, which thus behaves as an autonomous nanodevice.[5] Responsive porous switchable framework materials based on a molecular switch incorporated in the backbone responds to a light stimulus. The efficient and quantitative bulk photoisomerization of the incorporated molecular switch takes advantage of the porosity of the framework and the consequent gas adsorption capaci

Dynamic building blocks such as molecular switches and motors engineered in permanently porous solids provide fascinating opportunities to modulate properties with external stimuli and achieve complex behaviors beyond those exhibited by the individual components. Highly porous, yet stable architectures, denominated porous switchable frameworks (PSFs), were engineered to sustain the effective isomerization of molecular switches in the solid state. We fabricate Porous Aromatic Frameworks (PAFs) with bistable molecular switches based on overcrowded alkene incorporated in the backbone of the materials. Dibrominated molecular photoswitches were copolymerized with porogenic building blocks, thus generating highly porous 3D frameworks which display BET surface areas as high as 3950 m2 g-1 and provide large free volumes that enable the conformational changes associated with the photoisomerization process.1 Indeed, upon U.V. light irradiation, solid-state 13C NMR spectroscopy demonstrates the quantitative isomerization of the light-responsive switches. Moreover, the local isomerization induced by light irradiation affects the overall porosity of the framework and modulates the bulk gas sorption properties. We extend our strategy engineering a hexadentate monomer containing an overcrowded alkene photoswitching core.2 Yamamoto homocoupling reaction yields swellable and hierarchical micro- and mesoporous architectures with densely integrated photoswitches, that can switch between stable and metastable state upon selective light irradiation. Upon light and chemical stimuli, the flexible framework endowed with hierarchical porosity can explore three unique and distinct porosity states that can be accessed in sequence. In-situ construction of spiropyran moieties with tailored functionality and precise responsivity produces highly porous dynamic materials which undergo reversible transformation of spiropyran to zwitterionic merocyanine by chemical and physical stimulation.3 These m

The study of motion in solids is a timely topic. The fabrication of materials such as Metal-Organic Frameworks (MOFs) provide a robust, yet often flexible, scaffold with excess free volume where embedded molecular switches, motors and rotors are free to move.[1] In turn, functional properties can be then imposed or modulated by controlling the rotation of said moieties inside the framework.[2] Namely, MOFs embedded with dipolar molecular rotors are emerging as an interesting class of compounds for their ability to respond to static or oscillating electric fields. In this work, we selected a bicyclopentanedicarboxylate-based (FTR) aluminum MOF (Al-FTR) and its dipolar, fluorinated analogue (Al-FTR-F2) to study the motion of these ligands at very low temperatures.[3] Computationally-informed structural analysis (PXRD, synchrotron-source) of the two MOFs reveals unusual, extensive dynamics down to temperatures as low as 2 K, reminiscent of liquid state mobility. Notably, the mobility in Al-FTR-F2, especially at extremely low temperatures, is due to a concerted dance of dipoles triggered by the interactions among nearest-neighbor rotors, which interconvert into each other thanks to a cascade mechanism. 1H T1 spin lattice relaxation times reveal a flat energy landscape with energy barriers as low as 17 cal/mol at 4 K. The subsequent study of the CO2-filled Al-FTR-F2 is then carried out in order to induce a coherence switch of the dipolar rotors, drastically impacting the overall configurational landscape. Similar compounds endowed with such controllable motional phenomena may find application in sensing or switching, the translation of light irradiation into movement and the control of solid-state dynamics with electrical fields minimizing energy dissipation. References [1] J. Perego, S. Bracco, C. X. Bezuidenhout, G. Prando, P. Carretta, A. Comotti, P. Sozzani. Nature Chem. (2020), 12, 845. [2] J. Perego, C. X. Bezuidenhout, S. Bracco, G. Prando, L. Marchiò, M. Negroni

The potentials of nanoporous materials for gas capture, separation and catalysis is emerging as an important research area for energy and environment issues. Our contribution was directed to the design and synthesis of customized materials for selective CO2 sequestration. MOFs and nanoporous polymers endowed with dynamic and responsive to chemical and photo-irradiation stimuli were prepared. In particular, a novel MOF family built by bipyridine-based pillars and layers of cycloaliphatic ligands were organized in stable interpenetrated architectures. Thy showed accessible galleries for favourable CO2 diffusion with well-defined pressure gates, useful for most effective deliverable-gas cycles. The steric and electronic properties of the pores was drove a virtually total selectivity towards nitrogen, as shown by competitive breakthrough runs under typical industrial fume release gas-mixture composition (15/85 N2/CO2). In turn, gas sorption influences the dynamic properties of the framework. The intriguing dynamic modulation was addressed by gas anisotropy and relaxation-time solid-state NMR measurements. Moreover, the integration of photo-active moieties in the very frame of polymeric porous frameworks (POPs or POPs) allowed for the construction of covalent contractile mano-sponges. The photo-switch as a monomeric unit exhibited a 100% conversion in the solid state, unlike photo-switch in solution. Structure expansion-contraction cycles corresponded to CO2 adsorption-desorption phenomenon.

Metal-organic frameworks (MOFs) present a platform that allows the insertion of ligands in a wide range of structural and chemical environments, thus tuning the ligand’s interactions with neighbouring moieties within the MOF. Conventionally, fast rotary dynamics is achieved by isolating molecular rotors, used as struts in MOFs, from their neighbours to reduce intermolecular interactions. Inserting bicyclo[1.1.1]pentandioate (FTR) rotors into a cubic framework yielded isolated rotors with a rotational energy barrier of only 6 cal/mol (Fig 1 A).1 The outstanding synthetic versatility of MOFs allows us to explore more dens arrangements of rotors to study the effect of cooperativity between the rotors. The FTR rotors were inserted into a pillar-and-layer Zn-MOF, and a geminal fluorinated FTR rotor into an Al-MOF. For the Zn-MOF, these rotors are still dynamic at very low temperatures through co-rotating pairs of rotors in a geared-like fashion. These geared molecular rotors have extremely low energy barriers for rotation (24 cal/mol) owing to the synchroneity of their rotation.2 Furthermore, the dipolar FTR-F2 rotor in the Al-MOF forms layers of interacting rotors oriented in different configurations. Contrary to expectation, these rotors are extremely dynamic down to 4K through a cooperative reorientation cascade of the dipolar rotors with a barrier for reorientation of ca. 17 cal/mol (Fig 1 B).3 REFERENCES 1. Perego, J.; Bracco, S.; Negroni, M.; Bezuidenhout, C. X.; Prando, G.; Carretta, P.; Comotti, A.; Sozzani, P., Nature Chem. 2020, 12, 845. 2. Perego, J.; Bezuidenhout, C. X.; Bracco, S.; G. Prando; L. Marchiò; M. Negroni; P. Carretta; P. Sozzani; and A. Comotti, JACS 2021, 143 (33), 13082-13090. 3. Perego, J.; Bezuidenhout, C. X.; Bracco, S.; Piva, S.; Prando, G.; Aloisi, C.; Carretta, P.; Kaleta, J.; Le, T. P.; Sozzani, P.; Daolio, A.; Comotti, A., Angew. Chem. Int. Ed 2023, 62, e202215893.

Within the ever-expanding field of porous materials, Metal-Organic Frameworks (MOFs) are well-known for their synthetic versatility and ability to capture greenhouse gases such as CO2. MOFs have also been shown to be able to support extensive dynamics without disrupting their primary architecture. Lately, MOFs were successfully employed to insert bicyclopentane-based rotors in the frameworks as ligands bridging the metal ions or cluster nodes, demonstrating extremely fast dynamics down to 2 K. [1]. The next step of the study would be to impose or modulate the properties of the material by controlling the rotation of said ligands inside the framework. [2] MOFs containing dipolar molecular rotors as linkers are emerging as an attractive class of compounds for their ability to interact with static or oscillating electric fields. Therefore, we built a bicyclopentane dicarboxylate-based (FTR) aluminum MOF (Al-FTR) and its dipolar, fluorinated analogue (Al-FTR-F2) (Figure 1, A), explored the rotor dynamics and CO2 capture ability. [3] To solve the crystal structures, we considered the arrangements of the CF2 dipoles as determined by the combination of molecular mechanics and PW-DFT in tandem with Rietveld refinement. Computationally-informed structural analysis of the two MOFs reveals very fast dynamics down to temperatures as low as 4 K, reminiscent of liquid state mobility, with strong agreements between 1H T1 spin-lattice NMR relaxation times and computational analysis. Notably, the mobility in Al-FTR-F2, especially at those extreme temperatures, is due to a concerted rotation of dipoles prompted by the interactions among nearest-neighbor rotors, interconverting into each other thanks to a cascade mechanism (Figure 1, B). The subsequent analysis of the CO2-filled Al-FTR-F2 reveals that gas filling can induce a coherence switch of the dipolar rotors, drastically impacting the overall configurational landscape (Figure 1, C). Similar compounds endowed with such controllab

Rotors, motors and switches in the solid state find a favorable playground in porous materials, especially in Metal Organic Frameworks (MOFs), thanks to their large free volume, which allows for fast dynamics. We focused on dynamic materials endowed with high responsiveness and under limited thermal noise conditions which enable the fabrication of molecular machines with low energy dissipation and controllable dynamics. We have realized a fast molecular rotor in the solid state whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures (2 K) [1,2]. The three-fold bipyramidal symmetry of the rotator conflicts with the four-fold symmetry of the struts within the cubic crystal cell of the zinc metal–organic framework, frustrating the formation of stable conformations. This allows for the hyperfast rotation of the bicyclic units persistent for several continuous turns, with an energy barrier of 6.2 cal mol−1 and a high frequency even at very low temperatures (1010 Hz below 2 K). Geared molecular rotors with negligible energy-requirements in MOFs enabled fast yet controllable and correlated rotary motion[3]. A MOF architecture was capable of supporting fast motional regimes (107 Hz), even at extremely cold temperatures, of two distinct and hypermobile rotors arranged in pillar-and-layer 3D arrays. The rotors explored multiple configurations of conrotary and disrotary relationships, switched on and off by thermal energy, an unprecedented cascade mechanism modulated by distinct energy barriers. Notably, fluorinated Metal-Organic Frameworks (MOFs), comprising a wheel-shaped ligand with geminal rotating fluorine atoms, produced a benchmark mobility of correlated dipolar rotors at 2 K, with practically null activation energy (Ea = 17 cal/mol), as supported by 1H T1 relaxation NMR, synchrotron radiation X-ray diffraction at 4 K and DFT modeling (Angew. Chem. Int. Ed. 2023 in press). Gas accessibility, shown by hyperpolarized

Achieving sophisticated juxtaposition of geared molecular rotors with negligible energy-requirements in solids enables fast yet controllable and correlated rotary motion to construct switches and motors. Our endeavor was to realize multiple rotors operating in a MOF architecture capable of supporting fast motional regimes, even at extremely cold temperatures. Two distinct ligands, 4,4′-bipyridine (bipy) and bicyclo[1.1.1]pentanedicarboxylate (BCP), coordinated to Zn clusters fabricated a pillar-and-layer 3D array of orthogonal rotors. Variable temperature XRD, 2H solid-echo, and 1H T1 relaxation NMR, collected down to a temperature of 2 K revealed the hyperfast mobility of BCP and an unprecedented cascade mechanism modulated by distinct energy barriers starting from values as low as 100 J mol-1 (24 cal mol-1), a real benchmark for complex arrays of rotors. These rotors explored multiple configurations of conrotary and disrotary relationships, switched on and off by thermal energy, a scenario supported by DFT modeling. Furthermore, the collective bipy-ring rotation was concerted with the framework, which underwent controllable swinging between two arrangements in a dynamical structure. A second way to manipulate rotors by external stimuli was the use of CO2, which diffused through the open pores, dramatically changing the global rotation mechanism. Collectively, the intriguing gymnastics of multiple rotors, devised cooperatively and integrated into the same framework, gave the opportunity to engineer hypermobile rotors (107 Hz at 4 K) in machine-like double ligand MOF crystals.

An anionic mechanism is used to create polymers and copolymers as confined to, or anchored to, high-surface-area porous nanoparticles. Linear polymers with soft and glassy chains, such as polyisoprene and polymethylmethacrylate, were produced by confined anionic polymerization in 3D networks of porous aromatic frameworks. Alternatively, multiple anions were generated on the designed frameworks which bear removal protons at selected positions, and initiate chain propagation, resulting in chains covalently connected to the 3D network. Such growth can continue outside the pores to produce polymer-matrix nanoparticles coated with anchored chains. Sequential reactions were promoted by the living character of this anionic propagation, yielding nanoparticles that were covered by a second polymer anchored by anionic block copolymerization. The intimacy of the matrix and the grown-in polymers was demonstrated by magnetization transfer across the interfaces in 2D 1H-13C-HETCOR NMR spectra.

Scintillators, materials that produce light pulses upon interaction with ionizing radiation, are widely employed in radiation detectors. In advanced medical-imaging technologies, fast scintillators enabling a time resolution of tens of picoseconds are required to achieve high-resolution imaging at the millimetre length scale. Here we demonstrate that composite materials based on fluorescent metal–organic framework (MOF) nanocrystals can work as fast scintillators. We present a prototype scintillator fabricated by embedding MOF nanocrystals in a polymer. The MOF comprises zirconium oxo-hydroxy clusters, high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from 9,10-diphenylanthracene ligand emitters. Their incorporation in the framework enables fast sensitization of the ligand fluorescence, thus avoiding issues typically arising from the intimate mixing of complementary elements. This proof-of-concept prototype device shows an ultrafast scintillation rise time of ~50 ps, thus supporting the development of new scintillators based on engineered fluorescent MOF nanocrystals.

Metal-Organic frameworks (MOFs) and porous molecular materials represent a new platform for achieving and exploring high-performance sorptive properties and gas transport. The key lies in the modular nature of these materials, which allows for tuning and functionalization towards improved gas capture. Self-assembly of polyfunctional molecules containing multiple charges, namely, tetrahedral tetra-sulfonate anions and bifunctional linear cations, resulted in a permanently porous crystalline material in which the channels are decorated by double helices of electrostatic charges that governed the association and transport of CO2 molecules.[1] An isoreticular series of Fe-MOFs with varying decoration of fluorine atoms within their channel walls as a method for modulating the CO2 adsorption properties.[2] In these systems we studied the guest recognition within the porous materials in relation to the structural moieties and modulation. A host of complementary experimental and computational techniques gives a holistic view of the host-CO2 properties towards the potential selective removal of CO2 from other gases. GCMC and DFT were employed for a detailed description of the CO2 diffusion and interactions in the porous materials. CO2–matrix adsorption enthalpies was accurately measured in-situ by simultaneous acquisition of microcalorimetric and volumetric-isotherm data. Accurate adsorption heats are very importation for sorption-based applications and devices, thus highlighting the importance of direct measurement of the adsorption heat. This also serves a way to benchmark the mathematical models and protocols for adsorption heats derived from sorption isotherms. References 1. Xing, G.; Bassanetti, I.; Bracco, S.; Negroni, M.; Bezuidenhout, C.; Ben, T.; Sozzani, P.; Comotti, A., Chemical Science 2019, 10 (3), 730-736. 2. Perego, J.; Bezuidenhout, C. X.; Pedrini, A.; Bracco, S.; Negroni, M.; Comotti, A.; Sozzani, P., Journal of Materials Chemistry A 2020, 8 (22), 11406-1141

Extensive development in microporous materials led to interesting physical properties and promising applications. Their structure enclose high free volume that enables fast dynamics even in condensed matter and allows the effective inclusion of molecular switches and machines with full retention of their molecular dynamical behavior in the solid state. Metal organic frameworks (MOFs) are characterized by a versatile chemistry and crystalline structures. A fast-rotating molecular rotor based on bicyclo[1.1.1]pentane–dicarboxylate moiety was installed in the 3D cubic structure of a highly porous zinc MOF1, thus isolating the individual rotor from each another. Moreover, the mismatch between the symmetry of the rotor and the symmetry of the carboxylate imposed by the cubic crystal structure generated a very shallow 12 fold potential well for rotational motion. Solid state NMR relaxation measurements and muon-spin spectroscopy performed at temperatures as low as 2 K allowed the determination of an activation energy as low as 6.2 cal mol-1, consistent with fast molecular reorientation in the GHz regime even at the lowest temperatures. Molecular dynamics simulations provides an understanding of the rotational motion at the nanoscale level consisting of continuous rotations above very shallow energy minima. This exciting results paved the way for the generation of materials endowed with fast dynamical properties even at very low temperatures. Installation of molecular machines in the solid state can upgrade stimuli-controlled nanometric changes into useful material properties due to the cooperative response of collection of molecular motors. A bistable overcrowded alkene was introduced in the main framework architecture of porous aromatic frameworks through the co-polymerization reaction of a photoswitch moiety and tetraphenylmethane molecule3. The frameworks displayed high porosity with surface areas as high as 4800 m2/g and provided enough free volume for the photoisomer

The solid state is typically not well suited to sustaining fast molecular motion, but in recent years a variety of molecular machines, switches and rotors have been successfully engineered within porous crystals and on surfaces. Here we show a fast-rotating molecular rotor within the bicyclopentane–dicarboxylate struts of a zinc-based metal–organic framework—the carboxylate groups anchored to the metal clusters act as an axle while the bicyclic unit is free to rotate. The three-fold bipyramidal symmetry of the rotator conflicts with the four-fold symmetry of the struts within the cubic crystal cell of the zinc metal–organic framework. This frustrates the formation of stable conformations, allowing for the continuous, unidirectional, hyperfast rotation of the bicyclic units with an energy barrier of 6.2 cal mol−1 and a high frequency persistent for several turns even at very low temperatures (1010 Hz below 2 K). Using zirconium instead of zinc led to a different metal cluster–carboxylate coordination arrangement in the resulting metal–organic framework, and much slower rotation of the bicyclic units. [Figure not available: see fulltext.].

The incorporation of photoswitchable molecules into solid-state materials holds promise for the fabrication of responsive materials, the properties of which can be controlled on-demand. However, the possible applications of these materials are limited due to the restrictions imposed by the solid-state environment on the incorporated photoswitches, which render the photoisomerization inefficient. Here we present responsive porous switchable framework materials based on a bistable chiroptical overcrowded alkene incorporated in the backbone of a rigid aromatic framework. As a consequence of the high intrinsic porosity, the resulting framework readily responds to a light stimulus, as demonstrated by solid-state Raman and reflectance spectroscopies. Solid-state 13C NMR spectroscopy highlights an efficient and quantitative bulk photoisomerization of the incorporated light-responsive overcrowded olefins in the solid material. Taking advantage of the quantitative photoisomerization, the porosity of the framework and the consequent gas adsorption can be reversibly modulated in response to light and heat. [Figure not available: see fulltext.].