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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.].

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.

Large Stokes shift fast emitters show a negligible reabsorption of their luminescence, a feature highly desirable for several applications such as fluorescence imaging, solar-light managing, and fabricating sensitive scintillating detectors for medical imaging and high-rate high-energy physics experiments. Here we obtain high efficiency luminescence with significant Stokes shift by exploiting fluorescent conjugated acene building blocks arranged in nanocrystals. Two ligands of equal molecular length and connectivity, yet complementary electronic properties, are co-assembled by zirconium oxy-hydroxy clusters, generating crystalline hetero-ligand metal-organic framework (MOF) nanocrystals. The diffusion of singlet excitons within the MOF and the matching of ligands absorption and emission properties enables an ultrafast activation of the low energy emission in the 100 ps time scale. The hybrid nanocrystals show a fluorescence quantum efficiency of ~60% and a Stokes shift as large as 750 meV (~6000 cm−1), which suppresses the emission reabsorption also in bulk devices. The fabricated prototypal nanocomposite fast scintillator shows benchmark performances which compete with those of some inorganic and organic commercial systems.

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 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 as supported by 2H solid-echo, 1H T1 relaxation NMR and DFT modeling. Chemical stimuli such as the use of CO2 diffused through the open pores changed dramatically the global rotation mechanism and rotor speed. Furthermore, motors were inserted into porous frameworks and metal-organic frameworks wherein two distinct linkers with complementary light absorption-emission properties were integrated into the same material. Unidirectional motion was achieved by exposure to sun-light of the solid particles, which thus behave as autonomous nanodevices.[4] The visible-light-driven rotation of an overcrowded alkene-based molecular motor strut in a dual

Owing to their modular nature, Metal-Organic frameworks (MOFs) represent a new platform for achieving and exploring structural framework that allows for control over the ligand environment. This allows for tuning of the ligand properties towards potentially desired outcomes. Traditionally when inserting molecular rotors as struts into MOFs, the gaol is to isolate them and consequently lowering their reorientation energy barriers for fast rotary dynamics. We have achieved such a system of isolated bicyclo[1.1.1]pentandioate (FTR) rotors within a MOF structure which yielded an energy barrier for rotation of a couple calories per mole. [1] The outstanding synthetic versatility of MOFs allows us to insert the FTR rotor into a pillar-and-layer Zn-MOF where the rotors can interact with their neighbours (Fig 1 and 2). Contrary to expectations, these rotors navigate the rotational potential energy landscape in such a way to produce co-rotating pairs of rotors or geared molecular rotors. These geared molecular rotors have a very low energy barriers for rotation (24 cal/mol) owing to the synchroneity of their rotation. Additionally, the collective bipy-ring rotation are in concert with the framework structural dynamics that gives rise to controllable swinging between two identical arrangements in a dynamically disordered structure. Upon cool down to 160 K the framework become more ordered thus indicating that the reorientation dynamics of the bipy pyridyl rings are being stopped. This framework gymnastics is a good example of structural dynamics controlled by rotor reorientation dynamics. [2] 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 Journal of the American Chemical Society 2021,143 (33), 13082-13090.

The design and engineering of precise molecular building blocks expand the scope of porous materials and boost the development of innovative photonic, dynamic, and adsorptive materials. Light-responsive Porous Switching Frameworks (PSFs) with BET surface area as high as 3948 m2 g-1 were generated by co-polymerization of molecular motors with rigid tetrahedral building blocks.[1] The quantitative molecular photoisomerization in the solid state promotes the modulation of gas adsorption properties, generating light-responsive materials suitable for actively switching devices. Self-standing sensitized triplet-triplet annihilation (s-TTA) upconverting nanoparticles were developed by inclusion of a porphyrin unit (sensitizer) in the cavities of Porous Emitting Frameworks (PEFs) comprising highly luminescent diphenyl anthracene (DPA) units.[2] The proximity between the guest sensitizer and DPA emitters promotes effective energy transfer and an up-conversion quantum yield as high as 0.15, a record value for solid-state materials. Porous Aromatic frameworks (PAFs) provide a stable platform with ultra-high pore volume. Highly reactive anionic species were generated on the framework or diffused in the pores to promote anchored and confined polymerization.[3] The “ship-in-a-bottle” polymerization process generates intimately interdigitated nanocomposites proved by 2D 13C solid-state NMR. Moreover, the living nature of anionic polymerization allowed the fabrication of polymer-coated nanoparticles with sequential architecture. The adsorptive properties of POPs can be tailored for selective gas adsorption: calixarene-based POPs provide great opportunity for gas storage and separation proved by high-pressure sorption, adsorption-coupled calorimetry, and breakthrough measurements under flow condition.[4] References [1] F. Castiglioni, W. Danowski, J. Perego, F. K.-C. Leung, P. Sozzani, S. Bracco, S. J. Wezenberg, A. Comotti, B. L. Feringa, Nat. Chem. 2020, 12, 595–602. [2] J. Perego

Crystalline nanoporous architectures offer stimulating opportunities in designing rotors and motors in the solid state and exploring sorptive properties and gas transport. Molecular rotors in the solid state have been successfully engineered in porous materials, such as Metal Organic Frameworks (MOFs), thanks to their large free volume, which allows for fast dynamics. In particular, a ultra-fast molecular rotor, whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures, has been realized.(1) The rotor based on bicyclo[1.1.1]pentane–dicarboxylate (BCP) moiety was installed in the 3D cubic structure of a highly porous Zn-MOF, thus isolating the individual rotor from each another (Fig. 1a, b). Solid state NMR relaxation measurements 1H T1 and muon-spin spectroscopy(2) 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. Furthermore, pillared-MOFs built from two distinct ultrafast and interacting molecular rotors form a multidynamical architecture wherein the rotors experience sequential motional behaviour activated at distinct temperatures. The manipulation by chemical stimuli, such as CO2, which diffused from the gas phase into the porous matrix, resulted in the selective control over rotary dynamics.(3) CO2 diffusion in a porous crystalline material, in which the channels are decorated by double helices of electrostatic charges, has been described by solid state NMR. The remarkable CO2-matrix association allowed direct observation of the gas exploring the nanochannels and the identification of the specific interaction sites by 2D 1H-13C HETCOR MAS NMR experiments (Fig. 2), providing peculiar details about the role of electrostatic interactions in gas transport phenomena. The sorption performances and the extraordinary thermal stability up to 450 °C highlighted

Nanoporous materials offer stimulating perspectives in building molecular rotors in the solid state and exploring sorptive properties and gas transport. In this field a particularly prominent application of solid state NMR is the study of dynamic processes in solids and in the gas phase. Molecular rotors in the solid state find a favourable playground in porous materials, such as MOFs, thanks to their large free volume, which allows for fast dynamics. In particular, we have realized a ultra-fast molecular rotor in the solid state, whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures.1 The rotor based on bicyclo[1.1.1]pentane–dicarboxylate moiety was installed in the 3D cubic structure of a highly porous zinc MOF, thus isolating the individual rotor from each another (Fig. 1a, b). Solid state NMR relaxation measurements 1H T1 and muon-spin spectroscopy 2 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 (Fig. 1c). Self-assembly of polyfunctional molecules containing multiple charges, namely, tetrahedral tetra-sulfonate anions (TBS) and bi-functional linear cations (DAB), 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 (Fig. 2 a-c). The ionic patterning of the channels allows the establishment of high interactions of 35 kJ mol-1, ideal for CO2 capture/release cycles.3 The remarkable CO2-matrix association allowed direct observation of the gas exploring the nanochannels by 13C CP-MAS NMR spectroscopy and the identification of the specific interaction sites by 2D 1H-13C HETCOR MAS NMR experiments (Fig. 2d). References 1. J. Perego, S. Bracco, M. Negroni, C. X. Bezuidenhout, G. Prando, P. Carretta, A. Comotti, and

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.

The supramolecular capacity of calixarenes towards guests is largely consolidated; in contrast, the synthesis of porous calixarene-based frameworks by covalent bond formation is still a challenge. Our target was to yield 3D polymers and copolymers based on calixarenes for selective gas-capture, endowed with easy pore accessibility and specific sites, and builtviaa straightforward synthetic route. The covalent calixarene frameworks (CXFs) were prepared by the Yamamoto coupling reaction starting from tetrabromo calixarene propoxy- and methoxy-monomers of three stable calixarene (partial cone, effective cone, and 1,3-alternate) conformers and complete post-synthetic deprotection to achieve polar phenolic calixarene derivatives. Moreover, the copolymer of calixarene-based monomers with tetrabromo-tetraphenylmethane exhibited remarkable surface area up to about 3000 m2g−1. Smart architectures endowed with hierarchical porosity from micro- to meso-porosity showed notable sponge-like swellability by CO2, which was captured effectively at room temperature, even in competition with N2, yielding CO2removal in column breakthrough experiments. Indeed, CXFs displayed excellent CO2and CH4energy binding of 35 and 24 kJ mol−1, respectively. Ultramicropore sites were highlighted by Xe capture andin situdetection after a xenon diffusion time of a few milliseconds, by laser-assisted hyperpolarized129Xe NMR, revealing the accessibility of calixarene capsules and the available space. This synthetic route demonstrated the possibility to modulate at will the pore capacity and selectivity, displaying porous frameworks with two distinct pore families, wherein calixarene moieties play the role of small and selective sites. A contractile behavior of the frameworks was observed upon deprotection which produced more polar sites, due to the formation of hydrogen bond networks.

Rotors, motors and switches in the solid state find a favorable playground in porous materials, such as Metal Organic Frameworks (MOFs) and Porous Aromatic Frameworks (PAFs), thanks to their large free volume, which allows for fast 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). Continuos, unidirectional hyperfast rotation with an energy barrier of 6.2 cal/mol and a high frequency persistent for several turns are achieved (10 GHz below 2 K).[1] Responsive porous switchable framework materials endowed with light-responsive overcrowded olefins, took advantage of both the quantitative photoisomerization in the solid state and the porosity of the framework to reversibly modulate the gas adsorption in response to light. [2] Motors were inserted into metal-organic frameworks wherein two linkers with complementary absorption-emission properties were integrated into the same materials. Unidirectional motion was achieved by simple exposure to sun-light of the solid particles, which thus behave as autonomous nanodevices.[3] MOF nanocrystals comprising high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from diphenylanthracene ligand emitters showed ultrafast sensitization of the ligand fluorescence, thus supporting the development of new engineered scintillators.[4,5] References 1. A. Comotti, P. Sozzani et al Nature Chem. 2020, 12, 845. 2. A. Comotti, B. L. Feringa et al Nature Chem. 2020, 12, 595. 3. A. Comotti, B. L. Feringa et al J. Am. Chem. Soc. 2020, 142, 9048. 4.P. E. Sozzani, A. Comotti, A. Monguzzi et al Adv. Mater. 2019, 31, 1903309. 5. A. Comotti, A. Monguzzi et al Nature Photonics 2021, doi 10.1038/s41566-021-00769-z.

The search for new sophisticated functions integrated in porous solids prompted us to engineer switches and motors in metal-organic and covalent architectures for the construction of working nanodevices. 3D Porous Aromatic Frameworks were built with photo-active monomer units, and could be switched on command between two permanent states, entailing structure breathing and gas sorption switching. A fast molecular rotor in the solid state whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures (10 GHz below 2 K) was realized generating continuous, unidirectional hyperfast rotation with an energy barrier of 6.2 cal/mol. The energy transfer effect with radiation up-grading was also realized in Porous Emitting Frameworks (PEFs): porphyrin (red absorber) and diphenyl-antracene (blue emitter) were integrated in a 3D network showing very effective convertion of low energy light into photons of higher energy. With a similar concept, motors were inserted into metal-organic frameworks (MOFS), wherein two linkers with complementary absorption-emission properties were integrated in the same materials. The linkers were put in action by the visible light up-grading to UV-radiation, for fuelling the motors. MOF nanocrystals comprising high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from ligand emitters showed ultrafast sensitization of the ligand fluorescence, thus supporting the development of new engineered scintillators. A. Comotti, B. L. Feringa et al Nature Chem. 2020, 12, 595; A. Comotti, P. Sozzani et al Nature Chem. 2020, 12, 845; P. Sozzani, A. Comotti, A. Monguzzi et al Adv. Mater. 2019, 31, 1903309; A. Comotti, B. L. Feringa et al J. Am. Chem. Soc. 2020, 142, 9048; A. Comotti, A. Monguzzi et al Nature Photonics 2021, doi 10.1038/s41566-021-00769-z.

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 bi-functional 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 (Fig. 1). These channels electrostatically compliment the CO2 molecules and forms strong interactions of 35 kJ mol−1, ideal for CO2 capture/release cycles.[1] The CO2 adsorption properties were modulated for an isoreticular series of Fe-MOFs by varying the decoration of fluorine atoms within their channel (Fig. 2). 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 of 33 kJ mol−1 was accurately measured in-situ by simultaneous acquisition of micro-calorimetric and volumetric-isotherm data. Direct measurements of adsorption heats are not common and such data helps to validate mathematical models and protocols for sorption-derived adsorption enthalpies. [2]

Rotors, motors and switches in the solid state find a favorable playground in porous materials, such as Metal Organic Frameworks (MOFs) and Porous Aromatic Frameworks (PAFs), thanks to their large free volume, which allows for fast dynamics. We fabricated MOFs and PAFs with reorientable linkers and benchmark mobility also at very low temperature, to reduce the energy demand for motion-activation and light stimulus-response.[1] A fast molecular rotor in a Zn-MOF endowed with continuous, unidirectional hyperfast rotation with energy barrier of 6.2 cal/mol and high frequency persistent for several turns is achieved (Figure 1). Ligh responsive porous switchable frameworks took advantage of quantitative photoisomerization in the solid state and porosity of the framework to modulate the gas adsorption in response to light.[2] MOF nanocrystals comprising high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from ligand emitters showed ultrafast sensitization of the ligand fluorescence, thus supporting the development of new engineered scintillators.[3] References [1] A. Comotti, P. Sozzani et al. Nat. Chem. 12 (2020) 845; [2] A. Comotti, B. Feringa, et al. Nature Chem. 12 (2020) 595; [3] A. Comotti, A. Vedda, A. Monguzzi, et al. Nature Photonics (2021), https://doi.org/10.1038/s41566-021-00769-z. Financial support from the Italian Ministry of University and Research (MIUR) through the grant ‘Dipartimenti di Eccellenza-2017 Materials For Energy’ is acknowledged. This research was funded by the PRIN-2015CTEBBA-003.

Porous organic frameworks (PAFs) and Metal-organic frameworks (MOFs) were extensively studied in the past 20 years, widening the landscape of microporous materials. Responsive porous frameworks can be manipulated by means of external stimuli such as applied electric field or light irradiation, thus controlling their textural properties at will. Molecular photoswitches were co-polymerized with tetraphenylmethane generating 3D PAFs with high surface area (up to 4800 m2/g) and photo-responsive properties that quantitatively switch between stable and metastable state under U.V. light irradiation[1]. The localized and reversible photoisomerization reaction modified the bulk adsorptive properties of the porous materials with a 20% modulation of the adsorption capacity. These materials can be engineered to provide “on demand” adsorption properties for gas separation and gas storage/release. Scintillating materials are widely employed in high-energy particles detection and medical imaging. Innovative composite scintillators with high light yield and fast response time were developed embedding luminescent MOFs in a polymer matrix[2]. Highly emissive MOFs nanocrystals (ZrDPA) were synthetized by the assembly of 9,10-bis(4-carboxyphenyl)anthracene (DPA) and zirconium oxo-hydroxy cluster and dispersed in polymer matrixes to obtain self-standing monoliths. The MOF/polymer composites showed outstanding radioluminescence and scintillating properties with high light yields and scintillation rise time of ~ 50 ps, making them suitable for application in detectors for time-of-flight positron emission tomography (TOF-PET). [1] F. Castiglioni, W. Danowski, J. Perego, F. K.-C. Leung, P. Sozzani, S. Bracco, S. J. Wezenberg, A. Comotti, B. L. Feringa, Nature Chemistry. 2020, 12, 595. [2] J. Perego, I. Villa, A. Pedrini, E. C. Padovani, R. Crapanzano, A. Vedda, C. Dujardin, C. X. Bezuidenhout, S. Bracco, P. E. Sozzani, A. Comotti, L. Gironi, M. Beretta, M. Salomoni, N. Kratochwil, S. Gundac

Rotors, motors and switches in the solid state find a favorable playground in porous materials, such as Metal Organic Frameworks (MOFs), thanks to their large free volume, which allows for fast dynamics. We fabricated MOFs with reorientable linkers and benchmark mobility also at very low temperature, to reduce the energy demand for motion-activation and light stimulus-response. In particular, 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). The rotors were hosted within the struts of a low-density porous crystalline MOF and energetically decoupled from their surroundings. A key point was the unusual crossed conformation adopted by the carboxylates around the pivotal bond on the rotor axle, generating geometrical frustration and very shallow wells along the circular trajectory. Continuos, unidirectional hyperfast rotation with an energy barrier of 6.2 cal/mol and a high frequency persistent for several turns is achieved (10 GHz below 2 K).[1] Responsive porous switchable framework materials endowed with light-responsive overcrowded olefins, took advantage of both the quantitative photoisomerization in the solid state and the porosity of the framework to reversibly modulate the gas adsorption in response to light. [2] Motors were inserted into metal-organic frameworks wherein two linkers with complementary absorption-emission properties were integrated into the same materials. Therefore, unidirectional motion was achieved by simple exposure to sun-light of the solid particles, which thus behave as autonomous nanodevices.[3] MOF nanocrystals comprising high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from diphenylanthracene ligand emitters showed ultrafast sensitization of the ligand fluorescence, thus supporting the development of new engineered scintillators.[4] References

Microporous materials offer synthetic versatility allowing the generation of advanced materials with unique photonic and scintillating properties. Highly luminescent diphenylanthracene (DPA) moieties can be framed into Porous Aromatic Frameworks (PAFs) generating porous nanoparticles with high quantum yield in the solid state[1]. After the diffusion and tethering of sensitizer molecules in the accessible voids inside the materials, each nanoparticle operated as self-standing solid state upconverting materials with potential applications in bio-imaging and photovoltaics. Scintillating materials emit light under excitation with ionizing radiations. They are fundamental for particle physics detectors and for medical imaging. State of the art technologies based on inorganic or polymeric materials produce high light yields or fast time responses, but neither of these standard approaches provide both properties within the same material. An innovative approach based on Metal-Organic Frameworks nanocrystals embedded in polymer matrixes successfully produced composite scintillators with promising light yield and fast rise and scintillation times[2]. High-Z MOFs were generated by coordination of Zirconium-based oxo-hydroxy clusters and highly emissive DPA ligands allowing for the efficient sensitization of the ligand fluorescence. Modulated synthesis produced nanocrystalline MOFs with controlled particle sizes and shapes that can be easily embedded in a continuous polymer matrix to generate self-standing monoliths. The scintillating properties of these composites were characterized showing high light yields and scintillation rise time of ~ 50 ps. These outstanding properties provides fast detection of high-energy radiations and made them suitable for application in detectors for time-of-flight positron emission tomography (TOF-PET). [1] Perego, J.; Pedrini, J.; Bezuidenhout, C. X.; Sozzani, P. E.; Meinardi, F.; Bracco, S.; Comotti, A. and Monguzzi, A. Advanced Materials, 2019

Metal organic frameworks provide a versatile platform that can generate intriguing behaviours and innovative properties. Specifically, this contribution highlights our recent results related to the installation of highly dynamic molecular rotors in MOFs[1] and the development of fast scintillating MOFs and MOF/polymer composites for fast detection of high-energy radiations[2]. MOFs provide precise spatial disposition of organic struts and enough free volume to preserve the dynamic properties of molecular motors and rotors even in condensed matter. Molecular rotor bicyclo[1.1.1]pentane–dicarboxylate was installed in the 3D cubic structure of a highly porous zinc MOF[1] (figure A,B,C,D). Its dynamic behaviour was investigated with solid state NMR relaxation and muon-spin spectroscopy performed at temperatures as low as 2 K and molecular dynamic simulations, providing clear evidence of very fast molecular reorientation in the GHz regime even at the lowest temperatures, consistent with a low activation energy for rotational motion of 6.2 cal mol-1. High-Z MOFs were generated by coordination of zirconium-based clusters and highly emissive 9,10-bis(4-carboxyphenyl)anthracene (DPA) ligands allowing for the efficient sensitization of the linker fluorescence under high-energy radiation excitation (figure E,F). MOF nanocrystals were embedded in a continuous polymer matrix producing ultra-fast scintillators with rise time of ~ 50 ps and high light yields suitable for application as detectors for time-of-flight positron emission tomography (TOF-PET). [1] J. Perego, S. Bracco, M. Negroni, C. X. Bezuidenhout, G. Prando, P. Carretta, A. Comotti, and P. Sozzani, Nat. Chem. (2020), 12, 845. [2] J. Perego, I. Villa, A. Pedrini, E. C. Padovani, R. Crapanzano, A. Vedda, C. Dujardin, C. X. Bezuidenhout, S. Bracco, P. E. Sozzani, A. Comotti, L. Gironi, M. Beretta, M. Salomoni, N. Kratochwil, S. Gundacker, E. Auffray, F. Meinardi, A. Monguzzi, Nat. Photonics (2021) https://doi.org/10.1038

The synthesis of porous organic 3D frameworks, wherein amine, hydroxyl and Li-alkoxide functions were built directly on the monomer-unit carbon core, realizes improved interactions with target gases. CO2 was retained by the amine group with a remarkable energy of 54 kJ mol-1, while 2D MAS NMR provided rare evidence of amine-to-gas short-distance interactions. Frameworks containing hydroxyl and Li-alkoxide functions show optimal interaction energies with CH4 of up to 25 kJ mol-1. The light network of 3-branch building units ensures the expandability of the nano-sponges.

Porous aromatic frameworks (PAFs) were engineered to generate solid-state upconverting materials that emit higher energy photons under a suitable light stimulus [1]. Fluorescent PAFs were generated by the inclusion of diphenylanthracene moieties in a low-density 3D porous frameworks that maintained the optical properties of the emitting chromophores in the solid-state. Upon inclusion of a suitable sensitizer (a metallo-porphyrin) inside the nanometer-sized pores, the copolymer displayed sensitized photon upconversion with a quantum yield as high as 15%, a record value for solid-state materials. Moreover, it was possible to tether the sensitizer to the porous matrix through a stable covalent bond, generating self-standing upconverting nanoparticles that can be possibly applied in photovoltaics and bio-imaging. PAFs can also be engineered as light-responsive materials. The co-polymerization of a photoswitch with tetraphenylmethane generated porous networks that provided the free volume for the photoisomerization of the overcrowded alkene [2]. Under UV light irradiation, the quantitative photoisomerization led to structural changes and modulated the CO2 adsorptive properties of the material. The process is reversible by irradiation or heating leading to a cyclable material.

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.

L'attività di ricerca si è occupata della progettazione, sintesi e caratterizzazione di materiali porosi. Diverse linee di ricerca sono state perseguite. Materiali porosi per l'assorbimento selettivo e lo stoccaggio di gas. Le proprietà di una serie di polimeri porosi organici sono state studiate attraverso misure di assorbimento di gas e misure di risonanza magnetica nucleare dello stato solido in presenza di una fase gassosa per comprendere la natura delle interazioni tra le molecole ospiti e le pareti dei canali. In particolare, si è verificata l'elevata energia di interazione tra le molecole di anidride carbonica e gruppi amminici alifatici che genera un'efficiente trasferimento di magnetizzazione tra gli idrogeni del gruppo amminico e il carbonio dell'anidride carbonica. Polimeri iper-reticolati porosi e polimeri organici porosi sono stati studiati mediante assorbimento di metano ad alta pressione (fino a 180 bar) per possibili applicazioni per lo stoccaggio di gas naturale in presenza di reticoli porosi (ANG). Durante il periodo all'estero presso il Bernal Institute sotto la supervisione del Prof. M.J. Zaworotko mi sono occupato dello sviluppo di una serie di framework metallo-organici che presentano flessibilità strutturale. In presenza di un opportuno gas o vapore i reticoli sintetizzati danno luogo a una transizione di fase tra una fase compatta e una fase porosa in maniera repentina. Questo meccanismo è attualmente molto studiato per le possibili applicazioni nell'ambito dello stoccaggio e separazione dei gas. Reticoli metallo-organici contenenti rotori molecolari. Due nuovi reticoli porosi metallo-organici sono stati sviluppati e le loro proprietà di assorbimento e termiche sono state caratterizzate. Inoltre, i due sistemi contengono un rotore molecolare molto mobile anche alle basse temperature come dimostrato da esperimenti di risonanza magnetica nucleare dello stato solido. Materiali porosi per applicazioni nella fotonica. Sono stati sintetizzat, The research activity focused on the design, synthesis and characterization of porous organic and hybrid materials. Porous materials for selective gas adsorption and storage. Tailored porous organic frameworks bearing different functional groups have been investigated via gas adsorption analyses and in situ spectroscopic techniques to understand the interaction between the guest phase and the primary adsorption sites installed on pore walls. Specifically, aliphatic amines interact strongly with carbon dioxide molecules resulting in an isosteric heat of adsorption as high as 54 kJ/mol at low loading and this close-contact interaction has been characterized with 2D heterocorrelated NMR sppectroscopy. Hyper.crosslinked polymers and porous organic frameworks have been synthetized and their performance towards high pressure (up to 180 bar) methane adsorption have been evaluated to assess their potential applications in adsorbed natural gas technology (ANG). During a period at Bernal institute (Limerick, Ireland) under the supervision of Prof. M. J. Zaworotko, I developed novel switching metal-organic frameworks that display guest-induced phase transitions between close phases and a porous open phase. During the close to open phase transitions the coordination sphere of the zinc cations inside the structures changes from a square pyramidal to a tetrahedral geometry. Moreover, the threshold pressure for gas adsorption can be manipulated through a mixed-linker approach. These materials are currently investigated for applications in gas storage and separation. Metal-organic frameworks with intrinsic dynamics. Metal organic frameworks built up with rigid aliphatic linkers have been developed and their adsorptive and thermal properties fully characterized. These materials display ultra-fast rotational dynamic even at very low temperature. An in-depth solid state NMR study has been conducted to understand the fast rotation of the organic strut and the influence of guest species

The conversion of low-energy light into photons of higher energy based on sensitized triplet–triplet annihilation (sTTA) upconversion is emerging as the most promising wavelength-shifting methodology because it operates efficiently at excitation powers as low as the solar irradiance. However, the production of solid-state upconverters suited for direct integration in devices is still an ongoing challenge owing to the difficulties concerning the organization of two complementary moieties, the triplet sensitizer, and the annihilator, which must interact efficiently. This problem is solved by fabricating porous fluorescent nanoparticles wherein the emitters are integrated into robust covalent architectures. These emitting porous aromatic framework (ePAF) nanoparticles allow intimate interaction with the included metallo-porphyrin as triplet sensitizers. Remarkably, the high concentration of framed chromophores ensures hopping-mediated triplet diffusion required for TTA, yet the low density of the framework promotes their high optical features without quenching effects, typical of the solid state. A green-to-blue photon upconversion yield as high as 15% is achieved: a record performance among annihilators in a condensed phase. Furthermore, the engineered ePAF architecture containing covalently linked sensitizers produces full-fledge solid-state bicomponent particles that behave as autonomous nanodevices.

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

Our scientific activity is focused on polymerizations in porous materials and the control of solid state reactions as well as on the formation in situ of new complex architectures with polymers. The project exploits both the unprecedented potentials of porous materials presently in use and the properties induced to the polymers e.g. stereochemistry, chain alignment and morphology control: the matrices range from fully-organic covalent frameworks and metal-organic frameworks to porous molecular crystals of biological origin. The extraordinary surface areas (BET> 5000 m2/g) and pore capacity exhibited by porous aromatic frameworks (PAFs), which are themselves polymeric architectures[1] interconnected by covalent bonds, allow sorption of a large amount of monomers to form high-molecular-mass polymers tightly interwoven with the porous matrix [2]. Polyacrylonitrile (PAN) polymerized by this methodology could undergo in-situ thermal transformation to semi-conductive or conductive polymers and carbon nano-fibers. PAN was also synthesized in the form of isotactic polymer within the nanochannels of dipeptide porous crystals which were used as sacrificial polymerization vessels [3]. The crystalline matrix sublimed away at 250 °C after the polymer intramolecular reaction to yield a rigid 'ladder polymer', which retained the morphology of the crystal scaffold. Morphological control has also been obtained starting from mesoporous silica to fabricate polymeric micro-objects [4]. In the case of metal-organic host framework the innovative idea was to make the host participating in the polymerization with two reactive vinyl pendant groups, that resulted in a cross-linked network [5]. The crystal scaffold of the host was removed except where it participates in the cross-linking reaction and acts as clipping point for the aligned polymer chains. Although the polymer chains grow in the atactic configuration, they exhibit periodic order since are kept in register by the molecular clips

High surface area 3D polymers represent one of the most promising classes of porous materials because of their high gas uptake and stability to thermal and chemical degradation. A series of porous organic polymers with aromatic building units have been synthesized and compared to explore their high-pressure performance as adsorbents of gases of relevant importance for energy and the environment. Particular attention was paid to methane storage up to pressures as high as 180 bar at ambient temperature. Porous polymers were prepared starting from a wide choice of spatially expanded aromatic monomers: a systematic change in the number of rings, variable size and shape was taken under consideration. The high number of rings (up to 6), which act as multiple reactive sites and form a number of connections between the multi-dentate nodes, result in an extensive cross-linked framework. Condensation was obtained by two alternative synthetic routes, viz., Yamamoto cross-coupling and Friedel-Crafts alkylation reactions. The structural characteristics and high stability of the porous polymers, even to mechanical compression, were carefully determined by several methods, including 1D and 2D solid state NMR, FT IR and thermal analyses. The CH4 uptake in the porous polymers allowed an understanding of the incremental response to pressure, up to extremely high values, and the exploitation of the extensive pressure range to customize the gas adsorption/desorption cycles for storage and transportation. Owing to the notable presence of large mesopores and network flexibility, combined with high surface area, a remarkable gain at high pressure was achieved, ensuring a highly competitive uptake/delivery efficiency. At 180 bar, adsorption values up to 445 cm3 STP g-1 were measured for porous organic polymers such as carbazolyl- and triptycene-based materials. The benchmark of these materials PAF1 reaches the value of 916 cm3 STP g-1 of adsorbed CH4, exceeding the performance of most of t

The fabrication of porous architectures for the confinement of gases and polymer chains to pores is a challenging research area. The matrices range from fully-organic and metal-organic frameworks to porous molecular crystals of synthetic and biological origin, such as dipeptides.[1] We were mostly intrigued in comparing the matrices depending on the nature of the interactions, pore shape, surface area and pore capacity. Like gases, flexible polymer chains can diffuse inside the galleries undergoing severe steric requirements which tune their conformations, dynamics and properties. Fast-1H, 19F and 2D hetero-correlated MAS NMR spectroscopies played a key role in determining the host-guest interactions at the interfaces and the relationships between the components. A few case studies will be highlighted. A peculiar kind of porous crystalline solid derives from the use of hard and soft interactions in a hierarchical construction. Primary supramolecular toroidal structures are formed by robust metal-organic bonds: they can self-assemble four-by-four into the shape of Platonic solids, held together by van der Waals and coulombic interactions.[2] Anions play a major role in modulating the architectures. The 3D crystalline structures are permanently porous and able to entrap reversibly vapors and gases. In a further example, 1,3-butadiene vapors could be separated from other C4 hydrocarbon by a MOF matrix [3], which provides structural flexibility and unique guest-responsive accommodation. Regarding the relevant issue of manipulating and transforming polymer chains in a confined environment, we varied the conducting properties of polyacrylonitrile chains by thermal transformation into graphitized nanofibers.[4] Moreover, isolation of single polysilane chains increased the rate of carrier mobility in comparison with that in the bulk state due to the elimination of the slow interchain hole-hopping.[5] The main chain conformation of polysilane could be controlled by changing