A luminescent Zr­(IV)-based metal–organic framework (MOF), with the underlying fcu topology, encompassing a π-conjugated organic ligand with a thiadiazole functionality, exhibits an unprecedented low detection limit of 66 nM for amines in aqueous solution. Markedly, this ultralow detection is driven by hydrogen-bonding interactions between the linker and the hosted amines. This observation is supported by density functional theory (DFT) calculations, which clearly corroborate the suppression of the twisting motion of thiadiazole core in the presence of amine, reducing significantly the nonradiative recombination pathways and subsequently enhancing the emission intensity. Credibly, nicotine regarded as a harmful chemical and bearing an amine pending group is also detected with high sensitivity, positioning this MOF as a potential sensor for practical environmental applications. This finding serves also as a benchmark to understand the sensing mechanism in MOFs.

Rational design and construction of metal-organic frameworks (MOFs) with intricate structural complexity are of prime importance in reticular chemistry. We report our latest addition to the design toolbox in reticular chemistry, namely the concept of merged nets based on merging two edge-transitive nets into a minimal edge-transitive net for the rational construction of intricate mixed-linker MOFs. In essence, a valuable net for design enclosing two edges (not related by symmetry) is rationally generated by merging two edge-transitive nets, namely (3,6)-coordinated spn and 6-coordinated hxg. The resultant merged-net, a (3,6,12)-coordinated sph net with net transitivity [32] enclosing three nodes and two distinct edges, offers potential for deliberate design of intricate mixed-linker MOFs. We report implementation of the merged-net approach for the construction of isoreticular rare-earth mixed-linker MOFs, sph-MOF-1 to -4, based on the assembly of 12-c hexanuclear carboxylate-based molecular building blocks (MBBs), displaying cuboctahedral building units, 3-c tritopic ligands, and 6-c hexatopic ligands. The resultant sph-MOFs represent the first examples of MOFs where the underlying net is merged from two 3-periodic edge-transitive nets, spn and hxg. Distinctively, the sph-MOF-3 represents the first example of a mixed-linker MOF to enclose both trigonal and hexagonal linkers. The merged-nets approach allows the logical practice of isoreticular chemistry by taking into account the mathematically correlated dimensions of the two ligands to afford the deliberate construction of a mixed-linker mesoporous MOF, sph-MOF-4. The merged-net equation and two key parameters, ratio constant and MBB constant, are disclosed. A merged-net strategy for the design of mixed-linker MOFs by strictly controlling the size ratio between edges is introduced.

Supercapacitors (SCs) are important energy storage devices that are increasingly playing an important role in various applications. [1-6] Though SCs can offer high power density, they have lower energy density in comparison to batteries. [1] The high power density makes them suitable for applications such as uninterruptible power supply (UPS), portable tools, rubber-tired gantry crane, and emergency doors on airplanes. [1,2] However, in order to deploy SCs in automotive and grid storage applications, their energy density needs to be significantly uplifted. [7,8] To enhance the energy density of SCs, which is calculated using this equation (E = 0.5 C V 2), either the specific capacitance (C) or cell voltage (V) needs to be improved. [2,9] The C values of the SC device can be improved by tuning the intrinsic properties of the electrode material. [10] For example, employing pseudocapacitive electrode materials is an effective strategy to enhance the specific capacitance (C) of the SC. [8] Pseudocapacitive materials, in general, show high capacitance values in comparison to electrical double layer capacitor (EDLC) based materials due to their fast reversible electron transfer redox reactions. [8] On the other hand, the cell voltage (V), the second major factor which influences the energy density, is greatly controlled by device engineering. [8,11] Organic electrolyte based SC devices usually offer a higher voltage window in comparison to aqueous devices. [8,11] However, the former suffers from some disadvantages such as low ionic mobility, high cost, toxicity, and not being environmentally benign. [12] On the other hand, aqueous electrolyte based SCs go without the aforementioned disadvantages, but the conventional symmetric SCs with aqueous electrolyte are hampered by low voltage windows. [12] In case of aqueous electrolyte SCs, the voltage window can be significantly improved by constructing asymmetric supercapacitors (ASCs). [12,13] In ASCs, two different electrode materials are used separately for the negative and positive electrodes. [12,13] The complementary potential windows of the individual electrodes enable the ASC device to cross the thermodynamic break New covalent organic frameworks (COFs), encompassing redox-functionalized moieties and an aza-fused π-conjugated system, are designed, synthesized, and deployed as negative electrodes in asymmetric supercapacitors (ASC), for the first time. The Hex-Aza-COFs are synthesized based on the solvothermal condensation reaction of cyclohexanehexone and redox-functionalized aromatic tetramines with benzoquinone (Hex-Aza-COF-2) or phenazine (Hex-Aza-COF-3). The redox-functionalized Hex-Aza-COFs show a specific capacitance of 585 F g −1 for Hex-Aza-COF-2 and 663 F g −1 for Hex-Aza-COF-3 in a three-electrode configuration. These values are the highest among reported COF materials and are comparable with state-of-the-art pseudocapacitive electrodes. The Hex-Aza-COFs exhibit a wide voltage window (0 to −1.0 V), which allow the construction of a two-electrode ASC device b...

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