The design and synthesis of crystalline porous materials is a frontier research area, especially in photo(electro)catalysis, due to their fascinating semiconducting properties. In recent years, ...crystalline metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) have received much research attention in heterogeneous catalysis, ranging from chemical conversion to solar energy production. In addition, COFs with well-ordered framework structures have been extensively studied in the field of heterogeneous photocatalysis for water splitting to produce hydrogen (H2) and oxygen (O2). Due to the synergistic effect of crystallinity, porosity, and conjugation in their frameworks, COFs have been widely explored. In this Review, we aim to discuss the effect of crystallinity of COFs on hydrogen generation via photocatalytic water splitting. We then briefly summarize the basic mechanisms of photocatalytic hydrogen generation, the advantages of crystalline semiconductors over amorphous materials, and the strategic designs of crystalline COFs. In addition, the state-of-the-art developments of crystalline COFs as organic semiconductors for photocatalytic hydrogen evolution have been systematically reviewed. We believe that understanding the structure–property relationship and photocatalytic performance for hydrogen evolution with respect to the long-range structural order of COFs is essential for the further development of innovative crystalline COF-based semiconductors in real-time hydrogen generation applications.
Significant conductance enhancement can be achieved by topology modification of n-type semiconducting naphthalenediimide (NDI) as a molecular circuit. Hydrazine not only reduces electron-deficient ...NDI to NDI•–radical anions but also modifies the topology by selectively replacing the amino acid methyl esters from NDI 1 and forms a cyclic NDI nanorim. On treatment with hydrazine, the NDI 1 emission band at 525 nm gradually disappears, and a new band appears at 607 nm, presumably due to NDI oligomer formation. Eventually, a shiny black, almost insoluble precipitate of the NDI nanorim appeared. The cyclic NDI nanorim was characterized by powder X-ray diffraction, high-resolution mass spectrometry, Fourier transform infrared, and 13C CP-MAS NMR spectroscopy. Cyclic voltammetry (CV) of NDI 1 possesses two sequential one-electron cathodic waves at −0.4661 and −0.9456 V versus Ag/Ag+ due to NDI•– and NDI2– formation. However, CV of the NDI nanorim reveals four distinct reversible one-electron waves due to electronic communication between the four NDI redox centers within the nanorim. The I–V measurements show sevenfold conductance enhancements by topology modification from linear NDI to a nanorim.
Covalent organic frameworks (COFs) are an emerging class of crystalline materials that are attracting increasing attention due to their high porosity, crystallinity, and tunable properties. ...Consequently, the strategic design of COF-based photocatalysts for various applications, including energy and environmental remediation, has attracted considerable interest. In particular, the sustainable production of clean fuel - hydrogen (H
2
) - by water splitting is a promising means to meet the global energy demand and to address the atmospheric CO
2
concentration caused by the excessive use of fossil fuels. In this regard, COFs offer potential advantages due to their modular nature, which facilitates their rational design from suitable organic building blocks to achieve optimal properties of visible light harvesting properties and easy charge transport. As a result, extensive research has been devoted to the design of photoresponsive COFs for efficient water splitting to generate hydrogen. Here, we provide a comprehensive review of recent developments in the strategic design of COF-based photocatalysts for solar fuel production
via
water splitting. The various organic linkers used in the construction of photocatalytic COFs and their structure-property correlations are discussed in detail. The role of bandgap engineering in tuning the hydrogen evolution efficiency of COFs is also discussed. Furthermore, the current challenges and future perspectives of COF-based solid catalysts for green and sustainable clean fuel production are presented. Indeed, this review demonstrates the importance of COF-based photocatalysts for the visible-light-driven hydrogen evolution reaction (HER) and can be beneficial for the future design of photocatalytic systems.
Covalent organic frameworks provide a platform for the integration of functional organic linkers into ordered yet tunable two-dimensional frameworks to yield π-π stacked conjugated materials for photocatalytic water splitting for hydrogen generation.
Twist and release: The metal–organic polyhedron 1 synthesized from 5‐(prop‐2‐ynyloxy)isophthalic acid and Cu(NO3)2⋅ 3 H2O has a hydrophobic outer surface and a hydrophilic inner core. In an aqueous ...medium, the resulting polarity gradient led to the transformation of 1 into the 2D metal–organic framework 2. This unique phenomenon enabled the gradual release of entrapped drug molecules.
The experimental rate law for the Cu(I)-catalyzed azide−alkyne cycloaddition (CuAAC) reaction was found to vary in complex ways with concentration, the presence of chloride ion, and the presence of ...accelerating ligands. Several examples of discontinuous (“threshold behavior”) kinetics were observed, along with a decidedly nonlinear correlation of electronic substituent parameter with the rate of CuAAC reaction with p-substituted arylazides. The previously observed tendency of the CuAAC reaction to provide ditriazoles from a conformationally constrained 1,3-diazide was found to be affected by a class of polybenzimidazole ligands introduced in the accompanying article. Various lines of evidence suggest that the standard tris(triazolylmethyl)amine ligand binds less strongly to Cu(I) than its benzimidazole analogues. On the basis of these observations, it is proposed that (a) a central nitrogen donor provides electron density at Cu(I) that assists the cycloaddition reaction, (b) the three-armed motif bearing relatively weakly coordinating heterocyclic ligands serves to bind the metal with sufficient strength while providing access to necessary coordination site(s), (c) at least two active catalysts or mechanisms are operative under the conditions studied, and (d) pendant acid or ester arms in the proper position can assist the reaction by speeding the protiolysis step that cleaves the Cu−C bond of a Cu·triazolyl intermediate.
Covalent organic nanosheets (CONs) have emerged as a new class of functional two-dimensional (2D) porous organic polymeric materials with a high accessible surface, diverse functionality, and ...chemical stability. They could become versatile candidates for targeted drug delivery. Despite their many advantages, there are limitations to their use for target specific drug delivery. We anticipated that these drawbacks could be overturned by judicious postsynthetic modification steps to use CONs for targeted drug delivery. The postsynthetic modification would not only produce the desired functionality, it would also help to exfoliate to CONs as well. In order to meet this requirement, we have developed a facile, salt-mediated synthesis of covalent organic frameworks (COFs) in the presence of p-toluenesulfonic acid (PTSA). The COFs were subjected to sequential postsynthetic modifications to yield functionalized targeted CONs for targeted delivery of 5-fluorouracil to breast cancer cells. This postsynthetic modification resulted in simultaneous chemical delamination and functionalization to targeted CONs. Targeted CONs showed sustained release of the drug to the cancer cells through receptor-mediated endocytosis, which led to cancer cell death via apoptosis. Considering the easy and facile COF synthesis, functionality based postsynthetic modifications, and chemical delamination to CONs for potential advantageous targeted drug delivery, this process can have a significant impact in biomedical applications.
A GdIII‐based porous metal–organic framework (MOF), Gd‐pDBI, has been synthesized using fluorescent linker pDBI (pDBI=(1,4‐bis(5‐carboxy‐1H‐benzimidazole‐2‐yl)benzene)), resulting in a ...three‐dimensional interpenetrated structure with a one‐dimensional open channel (1.9×1.2 nm) filled with hydrogen‐bonded water assemblies. Gd‐pDBI exhibits high thermal stability, porosity, excellent water stability, along with organic‐solvent and mild acid and base stability with retention of crystallinity. Gd‐pDBI was transformed to the nanoscale regime (ca. 140 nm) by mechanical grinding to yield MG‐Gd‐pDBI with excellent water dispersibility (>90 min), maintaining its porosity and crystallinity. In vitro and in vivo studies on MG‐Gd‐pDBI revealed its low blood toxicity and highest drug loading (12 wt %) of anticancer drug doxorubicin in MOFs reported to date with pH‐responsive cancer‐cell‐specific drug release.
MOF nanocarrier: A new GdIII‐based porous metal–organic framework, Gd‐pDBI, with an elongated rotatable linker (DBI=(1,4‐bis(5‐carboxy‐1H‐benzimidazole‐2‐yl)benzene) was synthesized. Gd‐pDBI is biocompatible, water‐stable, and acid/base‐tolerant. Mechanical grinding yielded nanocrystals with excellent water dispersibility, and they feature the highest loading of the anticancer drug doxorubicin (DOX) and cancer‐cell‐specific drug release.
Molecular defects critically impact the properties of materials. Here we introduce a paradigm called “isotopic labeling disassembly spectrometry” (ILDaS) that facilitates unprecedented precise ...experimental correlations between elastically inactive network defects (dangling chains and primary loops) and network formation kinetics and precursor structure. ILDaS is inspired by classical crossover experiments, which are often used to interrogate whether a reaction mechanism proceeds via an inter- or intramolecular pathway. We show that if networks are designed from labeled bifunctional monomers that transfer their labels to multifunctional junctions upon network formation, then the extent of junction labeling correlates directly with the number of dangling chains and cyclic imperfections within the network. We demonstrate two complementary ILDaS approaches that enable defect measurements with short analysis times, low cost, and synthetic versatility applicable to a broad range of network materials including polydisperse polymer precursors. The results will spur new experimental and theoretical investigations into the interplay between polymer network structure and properties.
Peripheral nerve injury (PNI) is a serious clinical health problem caused by the damage of peripheral nerves which results in neurological deficits and permanent disability. There are several factors ...that may cause PNI such as localized damage (car accident, trauma, electrical injury) and outbreak of the systemic diseases (autoimmune or diabetes). While various diagnostic procedures including X-ray, magnetic resonance imaging (MRI), as well as other type of examinations such as electromyography or nerve conduction studies have been efficiently developed, a full recovery in patients with PNI is in many cases deficient or incomplete. This is the reason why additional therapeutic strategies should be explored to favor a complete rehabilitation in order to get appropriate nerve injury regeneration. The use of biomaterials acting as scaffolds opens an interesting approach in regenerative medicine and tissue engineering applications due to their ability to guide the growth of new tissues, adhesion and proliferation of cells including the expression of bioactive signals. This review discusses the preparation and therapeutic strategies describing in vitro and in vivo experiments using graphene-based materials in the context of PNI and their ability to promote nerve tissue regeneration.
•Peripheral nerve injuries result in neurological deficits and permanent disability.•A full recovery in patients with peripheral nerve injury is in many cases deficient or incomplete.•Graphene and its derivatives can be used for the preparation of scaffolds for neural tissue engineering.•The presence of graphene or derivatives in hybrid materials influences both cell adhesion and cell proliferation.
