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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.

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

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 realization of tunable and functionalized MOFs is a winning strategy for CO2 capture. Here we report on a series of robust Fe-MOFs with triangular channels constructed by rod-like fluorinated pyrazolate ligands, comprising an increasing number of fluorine atoms on the central p-phenylene core (F = 1, 2, and 4). This yielded a series of isoreticular frameworks, engineered with orientational flexibility of the fluorinated aryl rings pivoted on ethynyl groups with an sp2–sp soft rotary barrier, providing a stable axel, which supported reorientable C–F dipoles. A combined approach, including powder X-ray diffraction, multinuclear solid-state NMR (2D 1H–13C, 19F, hyperpolarized 129Xe NMR and distance measurements by paramagnetic shift), gas-adsorption and microcalorimetry, enabled the exhaustive description of the fluorinated ring arrangement and the organization of functionalized sites for accommodating CO2. In the tetrafluoro-aryl-derivative MOF, protrusion of perfluorinated rings towards the channel space plays a major role in CO2 capture. Partially fluorinated aryl rings of mono- and di-fluoro MOFs turn to retract into the channel-walls to form continuous ribbons of inter-strut supramolecular interactions, contributing to the robustness of the overall architecture. Detailed computational models obtained using GCMC and DFT of CO2 diffusion and interactions in MOFs showed how the gas molecules approach the channel walls. The highly occupied sites are aligned at the corners of the triangular channels, wherein fluorine atoms participate in host–CO2 interactions. A CO2–matrix adsorption enthalpy of 33 kJ mol−1, suitable for capture/delivery cycles, was accurately measured in situ by simultaneous acquisition of microcalorimetric and volumetric-isotherm data. Thus, the designed advantages of rotationally flexible fluorinated moieties were successfully explored.

Nudear magnetic resonance (NMR) spectroscopy is a key technique for molecular structure determination in solution. However, due to its low sensitivity, many efforts have been made to improve signal strengths and reduce the required substrate amounts. In this regard, dissolution dynamic nuclear polarization (DDNP) is a versatile approach as signal enhancements of over 10 000-fold are achievable. Samples are signal-enhanced ex situ by transferring electronic polarization from radicals to nuclear spins before dissolving and shuttling the boosted sample to an NMR spectrometer for detection. However, the applicability of DDNP suffers from one major drawback, namely, paramagnetic relaxation enhancements (PREs) that critically reduce relaxation times due to the codissolved radicals. PREs are the primary source of polarization losses canceling the signal improvements obtained by DNP. We solve this problem by using potassium nitrosodisulfonate (Fremy's salt) as polarization agent (PA), which provides high nuclear spin polarization and allows for rapid scavenging under mild reducing conditions. We demonstrate the potential of Fremy's salt, (i) showing that both H-1 and C-13 polarization of similar to 30% can be achieved and (ii) describing a hybrid sample shuttling system (HySSS) that can be used with any DDNP/NMR combination to remove the PA before NMR detection. This gadget mixes the hyperpolarized solution with a radical scavenger and injects it into an NMR tube, providing, within a few seconds, quantitatively radical-free, highly polarized solutions. The cost efficiency and broad availability of Fremy's salt might facilitate the use of DDNP in many fields of research.

A porous 3D selectively fluorinated framework (F-PAF1), robust yet flexible and with a surface area of 2050 m2 g-1, was synthesised by condensation of an ad hoc prepared fluorinated tetraphenylmethane (TPM) monomer to ensure homogenously distributed C-F dipoles in the swellable architecture. Tetradentate TPM was also the comonomer for the reaction with fluorinated difunctional monomers to obtain frameworks (FMFs) with a controlled amount of regularly spaced reorientable C-F dipoles. The isosteric heat of adsorption of CO2 was increased by 53% by even moderate C-F dipole insertion, with respect to the non-fluorinated frameworks. CO2/N2 selectivity was also increased up to a value of 50 for the difluoro-containing comonomer. Moreover, methane shows optimal interaction energies of 24 kJ mol-1.

Despite use of blended cements containing significant amounts of aluminum for over 30 years, the structural nature of aluminum in the main hydration product, calcium aluminate silicate hydrate (C-A-S-H), remains elusive. Using first-principles calculations, we predict that aluminum is incorporated into the bridging sites of the linear silicate chains and that at high Ca:Si and H2O ratios, the stable coordination number of aluminum is six. Specifically, we predict that silicate-bridging [AlO2(OH)(4)](5-) complexes are favored, stabilized by hydroxyl ligands and charge balancing calcium ions in the interlayer space. This structure is then confirmed experimentally by one- and two-dimensional dynamic nuclear polarization enhanced Al-27 and Si-29 solid-state NMR experiments. We notably assign a narrow Al-27 NMR signal at 5 ppm to the silicate-bridging [AlO2(OH)(4)](5-) sites and show that this signal correlates to Si-29 NMR signals from silicates in C-A-S-H, conflicting with its conventional assignment to a "third aluminate hydrate" (T ) phase. We therefore conclude that TAH does not exist. This resolves a long-standing dilemma about the location and nature of the six-fold-coordinated aluminum observed by Al-27 NMR in C-A-S-H samples.

Using muon-spin spectroscopy, we study the exceptional dynamical properties of rotating molecular struts engineered within a Zn-based metal-organic framework at cryogenic temperatures, where the internal motions of almost any other organic substance are quenched. Muon-spin spectroscopy is particularly suited for this aim, as the experimental evidence suggests several implantation sites for the muons, among which at least one directly onto the rotating moiety. The dynamics of the molecular rotors are characterized by the exceptionally low activation energy EA ∼ 30 cal mol-1. At the same time, we evidence a highly unusual temperature dependence of the dipolar interaction of muons with nuclear magnetic moments on the rotors, suggesting a complex influence of the rotations on the muon implantation and diffusion.

Il mio lavoro di tesi si è basato sulla caratterizzazione dei materiali porosi rivolgendo particolare attenzione alla ricerca di elementi dinamici all’interno delle strutture e allo studio dei gas adsorbiti. Sono riuscito a rilevare la presenza di rotori parafenilenici ultraveloci sia in cristalli molecolari porosi che in metal-organic framework (MOF). Uno studio più approfondito ha inoltre rivelato come questi moti siano influenzati dal gas adsorbito. Nello specifico l’energia di attivazione della rotazione aumenta in funzione della quantità di gas nei pori. Per meglio capire questa interazione è però fondamentale la conoscenza del comportamento dei gas nei materiali porosi. Ho pertanto rivolto la mia attenzione allo studio del moto di xeno e CO2 in diversi materiali. L’utilizzo combinato di NMR e calcoli ab initio si è rivelato fondamentale per la comprensione di questi fenomeni ed è stato possibile rivelare particolari caratteristiche tanto dei gas quanto dei materiali stessi. La complessità della diffusione all’interno dei canali si è anche presentata in modi insoliti come il moto elicoidale dell’anidride carbonica imposto dal potenziale elettrostatico. Volendo continuare lo studio dei gas nei pori, ho caratterizzato diversi porous aromatic framework (PAF) con la tecnica dello xeno iperpolarizzato. Questo non mi ha consentito solo di misurare con accuratezza le dimensioni dei pori ma anche calcolare l’energia di interazione tra lo xeno e le pareti dei canali. Desiderando espandere le mie conoscenze sull’iperpolarizzazione come tecnica NMR, ho passato sei mesi presso il gruppo del Prof. L. Emsley a Losanna imparando la dynamic nuclear polarization (DNP) nonché la sua applicazione a diversi materiali., My thesis work was based on the characterization of porous materials, paying particular attention to the research of dynamic elements within the structures and to the study of adsorbed gases. I was able to detect the presence of ultrafast paraphenylenic rotors in both porous molecular crystals and metal-organic frameworks (MOFs). A more detailed study has also revealed how these motions are influenced by the adsorbed gas. Specifically, the activation energy of the rotation increases as a function of the quantity of gas in the pores. To better understand this interaction, the knowledge of the behavior of gases in porous materials is fundamental. I turned my attention to the study of xenon and CO2 motion in different materials. The combined use of NMR and ab initio calculations proved to be fundamental for understanding these phenomena and it was possible to reveal particular characteristics both of the gases and of the materials. The complexity of the diffusion within the channels has also been presented in unusual ways as the helicoidal motion of carbon dioxide imposed by the electrostatic potential. To continue the study of pore gases, I characterized several porous aromatic frameworks (PAFs) with the hyperpolarized xenon technique. This not only allowed me to accurately measure the pore size but also to calculate the interaction energy between the xenon and the channel walls. To expand my knowledge on hyperpolarization as an NMR technique, I spent six months at the group of Prof. L. Emsley in Lausanne learning dynamic nuclear polarization (DNP) as well as its application to different materials.

A crystalline hydrogen-bonded framework with permanent porosity, built by rod-like struts and engineered to bear ultra-fast molecular rotors between two triple bonds, offers the possibility of controlling the rotational rates upon CO2 adsorption. CO2 enters the pores from the gas phase and reduces the rotational rates from the extremely fast regime of 107 Hz at 216 K to 105 Hz. The CO2-rotor interaction was evident from the 2H NMR response to the dynamics of the rotors in contact with CO2 in the crystal structure.

Porous molecular materials represent a new front in the endeavor to achieve high-performance sorptive properties and gas transport. Self-assembly of polyfunctional molecules containing multiple charges, namely, tetrahedral tetra-sulfonate anions and bifunctional linear cations, resulted in a permanently porous crystalline material exhibiting tailored sub-nanometer channels with double helices of electrostatic charges that governed the association and transport of CO2 molecules. The charged channels were consolidated by robust hydrogen bonds. Guest recognition by electrostatic interactions remind us of the role played by the dipolar helical channels in regulatory biological membranes. The systematic electrostatic sites provided the perfectly fitting loci of complementary charges in the channels that proved to be extremely selective with respect to N2 (S = 690), a benchmark in the field of porous molecular materials. The unique screwing dynamics of CO2 travelling along the ultramicropores with a step-wise reorientation mechanism was driven by specific host-guest interactions encountered along the helical track. The unusual dynamics with a single-file transport rate of more than 106 steps per second and an energy barrier for the jump to the next site as low as 2.9 kcal mol-1 was revealed unconventionally by complementing in situ13C NMR anisotropic line-shape analysis with DFT modelling of CO2 diffusing in the crystal channels. The peculiar sorption performances and the extraordinary thermal stability up to 450 °C, combined with the ease of preparation and regeneration, highlight the perspective of applying these materials for selective removal of CO2 from other gases.

Porous metal–organic frameworks (MOFs) and porous coordination polymers (PCPs) are ideal substrates for gas storage and separation. In particular, the complexation of transition metals with pyrazole-based ligands boosts both thermal and chemical stability of the resulting MOFs, making these materials superior candidates for practical and industrial applications. The introduction of fluorinated groups in MOFs can result in more hydrophobic structures with improved performances under humid conditions in real-life applications such as CO2 capture from flue gas. We synthesized three 1,4-bis(1H-pyrazol-4-ylethynyl)benzene (H2BPEB) derivatives, bearing one, two (in adjacent positions) and four fluorine atoms on the central aromatic core. These struts were exploited to build Zn(II), Ni(II) and Fe(III) architectures. Gas absorption and separation abilities of such resulting structures were extensively investigated towards N2, CO2 and CH4.

The enormous interest manifested in recent years for porous materials has generated efficient systems for adsorbing gases of great interest for energy and the environment, such as CO2, CH4 and H2. Our project is based on the design of porosity in combination with switchable dynamics and flexibility for gaining control over gas capture and selectivity. This approach is made possible by fabricating tetrahedral building blocks and rotor-on-axel molecular struts. The interaction of tetrahedral-shaped polyanions with linear difunctional organic cations (CPOS-5) produced tailored sub-nanometer channels with double helices of electrostatic charges governed the association and transport of CO2 molecules.1 The unique screwing dynamics of CO2 travelling along the ultramicropores with a single-file 106 step/s transport rate was revealed by in-situ 13C-NMR combined with CO2 DFT modelling. Highly symmetrical tetrahedral elements were designed to construct swellable porous adamantoid frameworks through co-operation of hydrogen bonds mounted on conformationally flexible groups.2 The flexibility of the porous crystals manifests itself in response to stimuli of selected gases: the contact with CO2, Xe and hexane triggers the enlargement of channel cross-section and capacity. The accomodation of CO2 and Xe in the channel chambers was revealed by synchrotron-light XRD, combined with Molecular Dynamics and DFT calculations. 129Xe NMR highlights gas dynamics while receiving the encoding of the shape and orientation of each visited cage. Ultra-fast molecular rotors were realized in porous crystals by engineering crystalline frameworks containing rod-like linkers as amphidynamic elements.3 The porous frameworks promise access to the control of rotary motion by chemical and physical stimuli. Rotor dynamics as fast as 1011 Hz (in the regime of conventional liquids) in properly designed porous crystals was hampered by a gas or vapor diffused to the cavities, such as CO2, iodine and hydrocarb

In recent years the interest manifested for porous materials has generated efficient systems for adsorbing gases of great interest for energy and the environment, such as CO2, CH4 and H2. Our project is based on the design of porosity in combination with switchable dynamics and flexibility for gaining control over gas capture and selectivity. This approach is made possible by fabricating tetrahedral building blocks and rotoron- axel molecular struts. The interaction of tetrahedral-shaped polyanions with linear difunctional organic cations (CPOS-5) produced tailored sub-nanometer channels with double helices of electrostatic charges governed the association and transport of CO2 molecules.1 The unique screwing dynamics of CO2 travelling along the ultramicropores with a single-file 106 step/s transport rate was revealed by in-situ 13C-NMR combined with CO2 DFT modelling (Figure 1). Highly symmetrical tetrahedral elements were designed to construct swellable porous adamantoid frameworks through co-operation of hydrogen bonds mounted on conformationally flexible groups.2 The flexibility of the porous crystals manifests itself in response to stimuli of selected gases: the contact with CO2, Xe and hexane triggers the enlargement of channel cross-section and capacity. The accomodation of CO2 and Xe in the channel chambers was revealed by synchrotron-light XRD, combined with Molecular Dynamics and DFT calculations. 129Xe NMR highlights gas dynamics while receiving the encoding of the shape and orientation of each visited cage. Ultra-fast molecular rotors were realized in porous crystals by engineering crystalline frameworks containing rod-like linkers as amphidynamic elements.3 The porous frameworks promise access to the control of rotary motion by chemical and physical stimuli. Rotor dynamics as fast as 1011 Hz (in the regime of conventional liquids) in properly designed porous crystals was hampered by a gas or vapor diffused to the cavities, such as CO2, iodine and hydroca

In the search for flexible molecular crystals endowed with porosity, we achieved the fabrication of expandable crystalline prototypal structures, which allow the absorption of gases, without modifying the crystal architecture. The design brings together highly symmetrical tetrahedral elements to construct swellable porous adamantoid frameworks through co-operation of eight surrounding hydrogen bonds mounted on conformationally flexible groups. The flexibility of the porous crystals manifests itself in response to stimuli of selected gases, which promote reversible conformational changes, inducing breathing in the molecular structure. The backbone of the reticular construction is based on the formation of the carboxylic dimers, which project outwards from the tetrahedral molecular core to consolidate the 3D framework. Contact with proper gases such as CO2, Xe and hexane triggers a 56-70% enlargement of the channel cross-section. The accommodation of CO2 and Xe in the channel chambers was revealed by synchrotron-light X-ray diffraction, combined with molecular dynamics and density functional theory (DFT) theoretical calculations. Rare experimental observations of xenon dynamics, in which Xe diffuses along the channels and experiences different chamber orientations in the crystal, were gathered by analysing 129Xe NMR chemical shift anisotropy profiles, which encode the shape and orientation of each visited cavity along the channel. The jump rate and activation energy experienced was uniquely established by exploring Xe atoms in their diffusional path. Nitrogen showed a low affinity to the matrix and was unable to enlarge the pores, thus it was excluded from the restrictive pores of the empty crystal. Given the properties of molecular crystals, it is possible to outline some advantageous aspects, such as simple design, easy self-assembly, solubility, reversible gas uptake and absence of metal ions, and they can thus be considered for eco-friendly gas capture and separat

BACKGROUND: This multicenter, prospective study evaluated the determinants of zero-fluoroscopy (ZFL) ablation of supraventricular tachycardias.METHODS AND RESULTS: Four hundred thirty patients (215 male, 55.4 +/- 22.1 years) with indication to electrophysiological study or ablation of supraventricular tachycardias were enrolled. All participating physicians agreed to follow the as low as reasonably achievable policy. A procedure was defined as ZFL when no fluoroscopy was used. The total fluoroscopy time inversely correlated to the number of procedures previously performed by each operator since study start (r=-0.112; P=0.02). Two hundred eighty-nine procedures (67.2%) were ZFL; multivariable analysis identified as predictors of ZFL: procedure after the 30th for each operator, compared with procedures up to the ninth (P=0.011; hazard ratio, 3.49; 95% confidence interval [ CI], 1.79-6.80); the type of arrhythmia (P=0.031; electrophysiological study and atrioventricular nodal reentry tachycardia ablation having the highest probability of ZFL; hazard ratio, 6.87; 95% CI, 2.08-22.7 and hazard ratio, 2.02; 95% CI, 1.04-3.91, respectively); the operator's (P=0.002) and patient's age (P=0.009). Among operators, achievement of ZFL varied from 0% to 100%; 8 (22.8%) operators achieved ZFL in <25% of their procedures; 17 (48.6%) operators achieved ZFL in >75% of their procedures. The probability of ZFL increased by 2.8% (hazard ratio, 0.98; 95% CI, 0.97-0.99) as patient's age decreased by 1 year. Acute procedural success was obtained in all cases.CONCLUSIONS: The use of 3-dimensional mapping system completely avoided the use of fluoroscopy in most cases, with very low fluoroscopy time in the remaining and high safety and effectiveness profiles. Achievement of ZFL was predicted by the type of arrhythmia, operator's experience, and patient's age

A challenging issue is the dynamics of nanoporous solids after the insertion of molecular rotors in their building blocks and promises access to the control of rotary motion by chemical and physical stimuli.[1] The combination of porosity with ultra-fast rotor dynamics was discovered in molecular crystals, covalent organic frameworks and MOFs by 2H spin-echo NMR spectroscopy and T1 relaxation times.[2-5] The rotors, as fast as 1011 Hz at 150 K, are exposed to the crystalline channels, which absorb CO2 and I2 from the gas phase, even at low pressures. Interestingly, the rotor dynamics can be switched on and off by vapor absorption/desorption, showing a remarkable change of material dynamics, which, in turn, produces a modulated physical response. Novel mesoporous organosiloxane frameworks allowed us to realize periodic architectures of fast molecular rotors on which C-F dipoles are mounted.[6] These dipolar rotors showed not only rapid dynamics (109 Hz at 325 K) in solid-state NMR experiments, but also a dielectric response typical of a fast dipole reorientation. Moreover, crystals with permanent porosity were exploited in an unusual way to decorate crystal surfaces with regular arrays of dipolar rotors. The inserted molecules carry alkyl chains which are included as guests into the channel-ends.[7] The rotors stay at the surface due to a bulky molecular stopper which prevents the rotors from entering the channels. The host-guest relationships were established by 2D solid-state NMR and GIAO HF ab initio calculations. In a final example, flexible molecular crystals were fabricated by a series of shape-persistent azobenzene tetramers that form porous molecular crystals in their trans configuration. The efficient trans→cis photoisomerization of the azobenzene units converts the crystals into a non-porous phase but crystallinity and porosity are restored upon Z→E isomerization promoted by visible light irradiation or heating. We demonstrated that the photoisomerization e

Nanoporous materials are excellent candidates for the fabrication of molecular rotors in the solid state and promise access to the control of rotary motion by chemical and physical stimuli.[1] The combination of remarkable porosity with fast rotor dynamics was discovered in molecular crystals, covalent organic frameworks and metal-organic frameworks (MOFs) by 2H spin-echo NMR spectroscopy and spin lattice T1 relaxation times.[2-4] A microporous MOF engineered to contain in its scaffold rod-like ligands [1,4-bis(1H-pyrazol-4-ylethynyl)benzene] (BPEB) showed extremely rapid 180° flip reorientation of the central p-phenylene unit with rotational rates of 1011 Hz at 150 K. Molecular rotors are exposed to the crystalline channels, which absorb CO2 and I2 even at low pressure. Interestingly, dynamics could be tuned by gas absorption/desorption, showing a remarkable change of material dynamics, which, in turn, produces a modulated NMR response. Crystal-pore accessibility of the MOF allowed the CO2 molecules to enter the cavities and control the molecular rotor spinning speed down to 105 Hz at 150 K (Figure). This strategy enabled the regulation of rotary motion by gas diffusion in the channels and the determination of the energetics of rotary dynamics in the presence of CO2, enlarging perspectives in the field of sensors and gas detection. Moreover, the insertion of dipoles onto molecular rotors in mesoporous organosilica architectures permits to obtain fast molecular rotors containing dynamic C-F dipoles. The dipolar rotors show not only rapid dynamics of the aromatic rings (109 Hz at 325 K) in the solid state NMR experiments, but also dielectric response typical of a fast dipole-reorientation under the stimuli of an applied electric field.[5] Regular arrays of dipolar molecular rotors can be also mounted on crystal surfaces in an unusual way, exploiting the formation of surface inclusion compounds. Guest molecule is comprised of a rotator, a stopper and a shaft: 2D 1H-13

A metal organic framework (MOF) engineered to contain in its scaffold rod-like struts featuring ultrafast molecular rotors showed extremely rapid 180 ° flip reorientation with rotational rates of 1011 Hz at 150 K. Crystal-pore accessibility of the MOF allowed the CO2 molecules to enter the cavities and control the rotor spinning speed down to 105 Hz at 150 K. Rotor dynamics, as modulated by CO2 loading/unloading in the porous crystals, was described by proton T1 and 2H NMR spectroscopy. This strategy enabled the regulation of rotary motion by the diffusion of the gas within the channels and the determination of the energetics of rotary dynamics in the presence of CO2

Porous crystalline dipeptides absorb, reversibly from the gas phase, a series of volatile fluorinated ethers in use as anesthetics. Their vapor pressure was considerably reduced, with favorable guest capture and release. Variable channel sizes were customized for selective sorption and pressure thresholds were observed in the narrowest pores. 1H, 13C and 19F MAS NMR coupled with ab initio conformational analysis and grand canonical Monte Carlo simulations highlight the guest loading and arrangement adopted in the congruent nanochannels, suggesting how the anesthetics can accommodate in biochemical receptors.

A challenging issue is the dynamics of porous solids and the insertion of molecular rotors in their building blocks, promising access to the control of rotary motion by chemical stimuli. The combination of porosity with ultra-fast rotor dynamics was discovered in molecular crystals and covalent frameworks, by 2H spin-echo NMR spectroscopy and T1 relaxation times.[1-3] The rotors, as fast as 107 Hz at 200 K, are exposed to the crystalline channels, which absorb CO2 and I2 vapors even at low pressure. Interestingly, the rotor dynamics can be switched on and off by vapor absorption/desorption, showing a remarkable change of material dynamics. Novel mesoporous organosiloxane frameworks allowed to realize periodic architectures of fast molecular rotors containing dynamic C-F dipoles in their structure.[4] The dipolar rotors showed not only the rapid dynamics of the aromatic rings (ca. 5108 Hz at 325 K), as detected by solid-state NMR spectroscopy, but also a dielectric response typical of a fast dipole reorientation under the stimuli of an applied electric field. Crystals with permanent porosity were exploited in an unusual way to decorate crystal surfaces with regular arrays of dipolar rotors. The inserted molecules carry alkyl chains which are included as guests into the channel-ends.[5] The rotors stay at the surface due to a bulky molecular stopper which prevents the rotors from entering the channels. The host-guest relationships were established by 2D solid-state NMR and GIAO HF ab initio calculations. Flexible molecular crystals were fabricated by a series of shape-persistent azobenzene tetramers that form porous molecular crystals in their trans configuration. The efficient trans→cis photoisomerization of the azobenzene units converts the crystals into a non-porous phase but crystallinity and porosity are restored upon Z→E isomerization promoted by visible light irradiation or heating. We demonstrated that the photoisomerization enables reversible on/off switchin

Molecular rotors, especially when bearing dipoles, are a challenging research field entailing a number of useful phenomena, such as switchable ferroelectricity, and the fabrication of dynamic elements of molecular motors in solids. The combination of remarkable porosity with ultra-fast rotor dynamics was discovered by our group in molecular crystals and covalent frameworks, by 2H spin-echo NMR spectroscopy and T1 relaxation times [1-3]. Molecular rotors, as fast as 107 Hz at 200 K, are exposed to the crystalline channels, which absorb CO2 and I2 vapors even at low pressure. Interestingly, the rotor dynamics could be controlled by I2 absorption/desorption, showing a remarkable change of material dynamics and suggesting the use of porous crystals in sensing and pollutant management. Novel mesoporous organosiloxane frameworks, obtained by a self-assembly process, allowed to realize periodic architectures of fast molecular rotors containing dynamic C-F dipoles in their structure (Fig. 1a) [4]. The dipolar rotors showed not only the rapid dynamics of the aromatic rings (ca. 5x108 Hz at 325 K) (Fig. 1b), but also a dielectric response typical of a fast dipole reorientation under the stimuli of an applied electric field. Molecular rotors were mounted on crystal surfaces exploiting the formation of surface inclusion compounds. Guest molecules engineered as three segments comprising a shaft, a stopper, and a rotator can interact with a porous crystal and insert the shaft into the bulk crystal, while the rotator lies on the surface[5]. The host-guest relationships were established by 2D solid state NMR and low rotational barriers were found by dielectric spectroscopy.

Porous architectures, thanks to their functional properties, offer great opportunities in several applicative fields. Our scientific activity is devoted to the fabrication of porous materials and spectroscopic observation of gases diffused into the channels as well as of polymers obtained in situ inside the cavities. The matrices range from fully-organic covalent frameworks and metal-organic frameworks to porous molecular crystals of both synthetic and biological origin.[1-6] The diffusion and localization of the gas molecules within the cavities were investigated by 2D 1H-13C PMLG HETCOR solid state NMR on samples loaded with naturally abundant and enriched 13CO2, showing the accessibility of cavities to guest molecules from the gas phase. In the case of confined polymerization stereochemistry, chain alignment and morphology of the final products were addressed. 2D 1H-13C and fast-1H MAS NMR spectroscopy played a key role in determining the host-guest interactions at the interfaces and the intimacy between the two components, providing extremely valuable information ever detected by other techniques.Another challenging issue is the dynamics of porous solids and the insertion of molecular rotors in their very building blocks, thus promising access to switchable organic dielectrics. The combination of porosity with ultra-fast rotor dynamics was discovered in molecular crystals and covalent frameworks, by 2H spin-echo NMR spectroscopy. [7,8] The rotors, as fast as 108 Hz at 240 K, are exposed to the crystalline channels, which absorb CO2 and I2 vapors even at low pressure. Interestingly, the rotor dynamics can be switched on and off by vapor absorption/desorption, showing a remarkable change of material dynamics. Novel mesoporous organosilica frameworks allowed to realize periodic architectures of fast molecular rotors containing dynamic C-F dipoles in their structure.[9] The mobile elements showed not only the rapid dynamics of the aromatic rings (ca. 108 Hz at 325 K