### Recent Submissions

• #### Material Design and Reticular Chemistry: Unveiling New Topologies through Face Decoration of Edge Nets

(Industrial & Engineering Chemistry Research, American Chemical Society (ACS), 2022-08-12) [Article]
There is a critical need for novel and made-to-order materials capable to address current and upcoming ecological, energetic, and economical global challenges pertaining to gas storage and separation and also catalysis, sensing, pollutant remediation, and more. For those purposes, materials with novel topologies must be assessed but first imagined and assembled. In this work, we propose 13 promising topologies, unveiled thanks to a rational but yet very simple method, relying on the systematic face decoration of edge nets. Nine of these topologies are disclosed for the first time, and many more can be obtained using the same methodology. We demonstrate their relevance to reticular chemistry by proposing hypothetical structures matching some of the promising topologies, all comprising readily accessible and known building blocks.
• #### Aggregation-Induced Fluorescence Enhancement for Efficient X-ray Imaging Scintillators and High-Speed Optical Wireless Communication

(ACS Materials Letters, American Chemical Society (ACS), 2022-07-29) [Article]
Aggregation of some chromophores generates very strong fluorescence signals due to the tight molecular packing and highly restricted vibrational motions in the electronically excited states. Such an aggregation-induced emission enhancement enables great strides in biomedical imaging, security screening, sensing, and light communication applications. Here, we realized efficient utilization of a series of aggregation-induced emission luminogens (AIEgens) in X-ray imaging scintillators and optical wireless communication (OWC) technology. Ultrafast time-resolved laser spectroscopic experiments and high-level density functional theory (DFT) calculations clearly demonstrate that a significant increase in the rotational energy barrier in the aggregated state of AIEgens is observed, leading to highly restricted molecular vibrations and suppressed nonradiative processes. AIEgen-based scintillators exhibit a high X-ray imaging resolution of 16.3 lp mm–1, making them excellent candidates for X-ray radiography and security inspections. In addition, these AIEgens show a broad -3-dB modulation bandwidth of ∼110 MHz and high net data rates of ∼600 Mb/s, demonstrating their high potential for application in the field of high-speed OWC.
• #### Engineering MOF surface defects in mixed matrix membranes: An effective strategy to enhance MOF/polymer adhesion and control interfacial gas transport

(Journal of Membrane Science Letters, Elsevier BV, 2022-07-15) [Article]
MOF/polymer adhesion in Mixed Matrix Membranes (MMMs) has been mainly enhanced so far via MOF and/or polymer functionalization to strengthen the interactions between the two components. This strategy, albeit effective, is generally accompanied by a drop in the permeability and/or selectivity performance of the MMMs. In this contribution, engineering structure defects at the MOF surfaces is proposed as an effective route to create pockets that immobilize part of the polymer chain, which is of crucial importance both to avoid plasticization issues and to enhance the MOF/polymer affinity while overcoming the adhesion/performance trade-off in MMMs. This engineered interfacial interlocking structure also serves as a bridge to accelerate the gas transport from the polymeric region towards the MOF pore entrance. This concept is showcased with a model MMM made of the prototypical UiO-66 MOF and the glassy Polymer of Intrinsic Microporosity-1 (PIM-1) and tested using CO2, CH4 and, N2 as guest species. Our computational findings reveal that a defective UiO-66 MOF surface improves the MOF/PIM-1 adhesion and contributes to accelerate the interfacial gas transport of the slender molecules CO2 and N2 and in a lesser extent of the spherical molecule CH4. This translates into a selective enhancement of the CO2 transport once combined with CH4 which paves the ways toward promising perspective for pre-combustion CO2 capture.
• #### Reticular Chemistry for the Construction of Highly Porous Aluminum-Based nia-Metal–Organic Frameworks

(Inorganic Chemistry, American Chemical Society (ACS), 2022-06-30) [Article]
Edge-transitive nets are regarded as appropriate blueprints for the practice of reticular chemistry, and in particular, for the rational design and synthesis of functional metal–organic frameworks (MOFs). Among edge-transitive nets, type I edge-transitive nets have unique coordination figures, offering only one edge-transitive target for their associated expressed net-cBUs. Here, we report the reticulation of the binodal edge-transitive (6, 6)-c nia net in MOF chemistry, namely, the deliberate assembly of trinuclear aluminum clusters and 6-connected hexacarboxylate ligands into highly porous nia-MOFs. Further studies reveal that Al-nia-MOF-1 shows promising attributes as a storage media for oxygen (O2) at high-pressure adsorption studies.
• #### Asymmetric pore windows in MOF membranes for natural gas valorization

(Nature, Springer Science and Business Media LLC, 2022-06-22) [Article]
To use natural gas as a feedstock alternative to coal and oil, its main constituent, methane, needs to be isolated with high purity1. In particular, nitrogen dilutes the heating value of natural gas and is, therefore, of prime importance for removal2. However, the inertness of nitrogen and its similarities to methane in terms of kinetic size, polarizability and boiling point pose particular challenges for the development of energy-efficient nitrogen-removing processes3. Here we report a mixed-linker metal–organic framework (MOF) membrane based on fumarate (fum) and mesaconate (mes) linkers, Zr-fum67-mes33-fcu-MOF, with a pore aperture shape specific for effective nitrogen removal from natural gas. The deliberate introduction of asymmetry in the parent trefoil-shaped pore aperture induces a shape irregularity, blocking the transport of tetrahedral methane while allowing linear nitrogen to permeate. Zr-fum67-mes33-fcu-MOF membranes exhibit record-high nitrogen/methane selectivity and nitrogen permeance under practical pressures up to 50 bar, removing both carbon dioxide and nitrogen from natural gas. Techno-economic analysis shows that our membranes offer the potential to reduce methane purification costs by about 66% for nitrogen rejection and about 73% for simultaneous removal of carbon dioxide and nitrogen, relative to cryogenic distillation and amine-based carbon dioxide capture.
• #### Separating molecules by their shapes can purify natural gas

(NATURE, Springer Science and Business Media LLC, 2022-06-22) [Article]
Membranes made from metal–organic frameworks contain modular pores that can separate mixtures of gas. By changing the shape of these pores to improve molecular separation, we produced a membrane that could remove nitrogen and carbon dioxide from natural gas in an energy-efficient and cost-effective way.
• #### Rational design of mixed-matrix metal-organic framework membranes for molecular separations

(Science, American Association for the Advancement of Science (AAAS), 2022-06-02) [Article]
Conventional separation technologies to separate valuable commodities are energy intensive, consuming 15% of the worldwide energy. Mixed-matrix membranes, combining processable polymers and selective adsorbents, offer the potential to deploy adsorbent distinct separation properties into processable matrix. We report the rational design and construction of a highly efficient, mixed-matrix metal-organic framework membrane based on three interlocked criteria: (i) a fluorinated metal-organic framework, AlFFIVE-1-Ni, as a molecular sieve adsorbent that selectively enhances hydrogen sulfide and carbon dioxide diffusion while excluding methane; (ii) tailoring crystal morphology into nanosheets with maximally exposed (001) facets; and (iii) in-plane alignment of (001) nanosheets in polymer matrix and attainment of [001]-oriented membrane. The membrane demonstrated exceptionally high hydrogen sulfide and carbon dioxide separation from natural gas under practical working conditions. This approach offers great potential to translate other key adsorbents into processable matrix.
• #### Evaluating the High-Pressure Volumetric CH4, H2, and CO2 Storage Properties of Denser-Version Isostructural soc-Metal–Organic Frameworks

(Journal of Chemical & Engineering Data, American Chemical Society (ACS), 2022-04-25) [Article]
The MOF platform based on soc topology showed recent developments for gas storage applications. soc-MOFs with very open structures, such as Al-soc-MOF-1, exhibited promising gravimetric storage performance but with compromised volumetric capacities. However, the volumetric capacity is a critical parameter to consider for vehicles such as trucks. The practical constraints under such circumstances are mainly linked to the tank volume required to accommodate adsorbents. In this work, the gas storage performances of dense soc-MOFs assembled from different metal precursors and 3,3′,5,5′-azobenzene tetracarboxylic acid, denoted as In-soc-MOF-1a, In-soc-MOF-1b, In-soc-MOF-1c, Ga-soc-MOF-1a, Fe-soc-MOF-1a, Fe-soc-MOF-1b, and Al-soc-MOF-1d, with 1a, 1b, 1c, and 1d representing NO3–, Cl–, Br–, and HO– counterions, respectively, were evaluated. Using the crystallographic densities of each MOF, volumetric uptakes were calculated from gravimetric values. The volumetric CH4, H2, and CO2 uptakes of the soc-MOFs showed a gain in storage capacity upon using denser versions, with a higher CH4 uptake of Fe-soc-MOF-1b (128 g L–1 at 50 bar) than the extended analogs (∼120 g L–1 for Fe-PBPTA-soc-MOF). The counteranions were also observed to have an impact on the volumetric capacities, with In-soc-MOF-1c > In-soc-MOF-1b > In-soc-MOF-1a for CH4 and the reverse order for H2 capacities. The performances are also comparable to those of most of the previously reported benchmark MOFs.
• #### Metal–Organic Frameworks in Mixed-Matrix Membranes for High-Speed Visible-Light Communication

(Journal of the American Chemical Society, American Chemical Society (ACS), 2022-04-12) [Article]
Mixed-matrix membranes (MMMs) based on luminescent metal-organic frameworks (MOFs) and emissive polymers with the combination of their unique advantages have great potential in separation science, sensing, and light-harvesting applications. Here, we demonstrate MMMs for the field of high-speed visible-light communication (VLC) using a very efficient energy transfer strategy at the interface between a MOF and an emissive polymer. Our steady-state and ultrafast time-resolved experiments, supported by high-level density functional theory calculations, revealed that efficient and ultrafast energy transfer from the luminescent MOF to the luminescent polymer can be achieved. The resultant MMMs exhibited an excellent modulation bandwidth of around 80 MHz, which is higher than those of most well-established color-converting phosphors commonly used for optical wireless communication. Interestingly, we found that the efficient energy transfer further improved the light communication data rate from 132 Mb/s of the pure polymer to 215 Mb/s of MMMs. This finding not only showcases the promise of the MMMs for high-speed VLC but also highlights the importance of an efficient and ultrafast energy transfer strategy for the advancement of data rates of optical wireless communication.
• #### Energy Transfer in Metal–Organic Frameworks for Fluorescence Sensing

(ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2022-02-17) [Article]
The development of materials with outstanding performance for sensitive and selective detection of multiple analytes is essential for the development of human health and society. Luminescent metal-organic frameworks (LMOFs) have controllable surface and pore sizes and excellent optical properties. Therefore, a variety of LMOF-based sensors with diverse detection functions can be easily designed and applied. Furthermore, the introduction of energy transfer (ET) into LMOFs (ET-LMOFs) could provide a richer design concept and a much more sensitive and accurate sensing performance. In this review, we focus on the recent five years of advances in ET-LMOF-based sensing materials, with an emphasis on photochemical and photophysical mechanisms. We discuss in detail possible energy transfer processes within a MOF structure or between MOFs and guest materials. Finally, the possible sensing applications of the ET-LMOF-based sensors are highlighted.
• #### Optimizing Host–Guest Selectivity for Ethylbenzene Capture Toward Superior Styrene Purification

(Chemistry of Materials, American Chemical Society (ACS), 2021-12-08) [Article]
The separation of ethylbenzene (EB) and styrene (ST) mixtures to obtain pure ST has been an enduring challenge for the petrochemical industry. So far, adsorptive separation using porous materials has mainly focused on capturing ST rather than EB, where high temperatures are needed to reactivate the sieving materials and collect the product. Here, we tuned the host–guest interactions in thienothiophene-based trianglimine (ThT-TI) macrocycles to selectively adsorb the unreacted EB over ST, after a dehydrogenation reaction, to readily provide pure ST without the need for further thermal treatments. This is the first report on the selective adsorptive separation of EB over ST using macrocycles as molecular hosts. Both crystalline and amorphous ThT-TI can be used to separate EB with 96% uptake capacity. Single-crystal and powder X-ray diffraction patterns suggest that this selective adsorption arises from a guest-induced structural reordering and involvement of the sulfur atoms in host/guest C–H···π interactions. We believe that this work paves the way for a new generation of molecular sieves that are designed to afford high-purity products by in situ capturing of the unreacted starting materials.
• #### Efficient Splitting of Trans-/Cis-Olefins Using an Anion-Pillared Ultramicroporous Metal–Organic Framework with Guest-Adaptive Pore Channels

(Engineering, Elsevier BV, 2021-12-08) [Article]
Trans-/cis-olefin isomers play a vital role in the petrochemical industry. The paucity of energy-efficient technologies for their splitting is mainly due to the similarities of their physicochemical properties. Herein, two new tailor-made anion-pillared ultramicroporous metal–organic frameworks (MOFs), ZU-36-Ni and ZU-36-Fe (GeFSIX-3-Ni and GeFSIX-3-Fe) are reported for the first time for the efficient trans-/cis-2-butene (trans-/cis-C4H8) mixture splitting by enhanced molecular exclusion. Notably, ZU-36-Ni unexpectedly exhibited smart guest-adaptive pore channels for trapping trans-C4H8 with a remarkable adsorption capacity (2.45 mmol∙g−1) while effectively rejecting cis-C4H8 with a high purity of 99.99%. The dispersion-corrected density functional theory (DFT-D) calculation suggested that the guest-adaptive behavior of ZU-36-Ni in response to trans-C4H8 is derived from the organic linker rotation and the optimal pore dimensions, which not only improve the favorable adsorption/diffusion of trans-C4H8 with optimal host–guest interactions, but also enhance the size-exclusion of cis-C4H8. This work opens a new avenue for pore engineering in advanced smart or adaptive porous materials for specific applications involving guest molecular recognition.
• #### Molecular engineering of intrinsically microporous polybenzimidazole for energy-efficient gas separation

(Applied Materials Today, Elsevier BV, 2021-12-04) [Article]
Polybenzimidazole (PBI) is a high-performance polymer that exhibits high thermal and chemical stability. However, it suffers from low porosity and low fractional free volume, which hinder its application as separation material. Herein, we demonstrate the molecular engineering of gas separation materials by manipulating a PBI backbone possessing kinked moieties. PBI was selected as it contains NH groups which increase the affinity towards CO$_2$, increase sorption capacity, and favors CO$_2$ over other gasses. We have designed and synthesized an intrinsically microporous polybenzimidazole (iPBI) featuring a spirobisindane structure. Introducing a kinked moiety in conjunction with crosslinking enhanced the polymer properties, markedly increasing the gas separation performance. In particular, the BET surface area of PBI increased 30-fold by replacing a flat benzene ring with a kinked structure. iPBI displayed a good CO$_2$ uptake of 1.4 mmol g$^{−1}$ at 1 bar and 3.6 mmol g$^{−1}$ at 10 bar. Gas sorption uptake and breakthrough experiments were conducted using mixtures of CO$_2$/CH$_4$ (50%/50%) and CO$_2$/N$_2$ (50%/50%), which revealed the high selectivity of CO$_2$ over both CH$_4$ and N$_2$. The obtained CO$_2$/N$_2$ selectivity is attractive for power plant flue gas application requiring CO$_2$ capturing materials. Energy and process simulations of biogas CO$_2$ removal demonstrated that up to 70% of the capture energy could be saved when iPBI was used rather than the current amine technology (methyl diethanolamine [MDEA]). Similarly, the combination of iPBI and MDEA in a hybrid system exhibited the highest CO$_2$ capture yield (99%), resulting in nearly 50% energy saving. The concept of enhancing the porosity of PBI using kinked moieties provides new scope for designing highly porous polybenzimidazoles for various separation processes.
• #### Nearly 100% energy transfer at the interface of metal-organic frameworks for X-ray imaging scintillators

(Matter, Elsevier BV, 2021-12) [Article]
In this work, we describe a highly efficient and reabsorption-free X-ray-harvesting system using luminescent metal-organic framework (MOF)-fluorescence chromophore composite films. The ultrafast time-resolved experiments and density functional theory calculations demonstrate that a nearly 100% energy transfer from a luminescent MOF with a high atomic number to an organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Such an unprecedented efficiency of interfacial energy transfer and the direct harnessing of singlet and triplet excitons of the TADF chromophore led to remarkable enhancement of radioluminescence upon X-ray radiation. A low detection limit of 256 nGy/s of the fabricated X-ray imaging scintillator was achieved, about 60 times lower than the MOF and 7 times lower than the organic chromophore counterparts. More importantly, this detection limit is about 22 times lower than the standard dosage for a medical examination, making it an excellent candidate for X-ray radiography.
• #### Ultrafast Aggregation-Induced Tunable Emission Enhancement in a Benzothiadiazole-Based Fluorescent Metal–Organic Framework Linker

(The Journal of Physical Chemistry B, American Chemical Society (ACS), 2021-11-30) [Article]
Aggregation-induced emission enhancement (AIEE) is a process recently exploited in solid-state materials and organic luminophores, and it is explained by tight-molecular packaging. However, solution-phase AIEE and its formation mechanism have not been widely explored. This work investigated AIEE phenomena in two donor–acceptor–donor-type benzodiazole-based molecules (the organic building block in metal–organic frameworks) with an acetylene and phenyl π-conjugated backbone tapered with a carboxylic acid group at either end. This was done using time-resolved electronic and vibrational spectroscopy in conjunction with time-dependent density functional theory (TD-DFT) calculations. Fluorescence up-conversion spectroscopy and time-correlated single-photon counting conclusively showed an intramolecular charge transfer-driven aggregate emission enhancement. This is shown by a red spectral shift of the emission spectra as well as an increase in the fluorescence lifetime from 746 ps at 1.0 × 10–11 to 2.48 ns at 2.0 × 10–3 M. The TD-DFT calculations showed that a restricted intramolecular rotation mechanism is responsible for the enhanced emission. The femtosecond infrared (IR) transient absorption results directly revealed the structural dynamics of aggregate formation, as evident from the evolution of the C≡C vibrational marker mode of the acetylene unit upon photoexcitation. Moreover, the IR data clearly indicated that the aggregation process occurred over a time scale of 10 ps, which is consistent with the fluorescence up-conversion results. Interestingly, time-resolved results and DFT calculations clearly demonstrated that both acetylene bonds and the sulfur atom are the key requirements to achieve such a controllable aggregation-induced fluorescence enhancement. The finding of the work not only shows how slight changes in the chemical structure of fluorescent chromophores could make a tremendous change in their optical behavior but also prompts a surge of research into a profound understanding of the mechanistic origins of this phenomenon. This may lead to the discovery of new chemical strategies that aim to synthesize novel chromophores with excellent optical properties for light-harvesting applications.
• #### Perovskite-Nanosheet Sensitizer for Highly Efficient Organic X-ray Imaging Scintillator

(ACS Energy Letters, American Chemical Society (ACS), 2021-11-27) [Article]
The weak X-ray capture capability of organic scintillators always leads to poor imaging resolution and detection sensitivity. Here, we realize an efficient and reabsorption-free organic scintillator at the interface of perovskite nanosheets using a very efficient energy transfer strategy. Our steady-state and ultrafast time-resolved experiments supported by density functional theory calculations demonstrate that an efficient interfacial energy transfer from the perovskite nanosheet to the organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Interestingly, we found that the direct harnessing of both singlet and triplet excitons of the TADF chromophores also contributed greatly to its remarkably enhanced radioluminescence intensity and X-ray sensitivity. A high X-ray imaging resolution of 135 μm and a low detection limit of 38.7 nGy/s were achieved in the fabricated X-ray imaging scintillator.
• #### Toward Liquid Phase Processable Metal Organic Frameworks: Dream or Reality?

(Accounts of Materials Research, American Chemical Society (ACS), 2021-11-11) [Article]