Organic Building Blocks Research Articles

Metal free synthesis of 1,3-diynes through Csp–Csp homo- and hetero-coupling reaction of terminal alkynes

Recent methodologies aimed at utilization of eco-friendly pathways and sustainable chemistry has turned out to be a convergent point in chemical research. With an objective to derive an economical, greener approach, herein, we report a mild and straightforward synthetic strategy to synthesize a series of substituted symmetrical and unsymmetrical 1,3-diyne derivatives. This metal free synthetic route catalyzed by N-Bromosuccinimide with tBuOK and KF as fluorine source at room temperature affords excellent yields upto 95% within 2 h. Such type of a greener and sustainable process was adopted for the development of organic building blocks or compounds with minimal waste afford to define the most of the Green Chemistry principles.

Luminescence modulation by twisting the branches of organic building blocks in uranyl-organic frameworks

Twisting the branches of an organic molecule will enhance luminescence; however, this is often accompanied by the rotation of the branches that will reduce luminescence, offering a contradiction. Thus, deep insight into this contradiction and creating some effective solutions to make a good trade-off have become critical but challenging. Here, we report a smart structural design to fine-tune the twisting of the branches of triangular organic building blocks through steric hindrance, including anchoring of organic units or further construction of uranyl-organic metal-organic frameworks (U-MOFs). Both theoretical calculations and experimental results disclose that the fluorescence performance in the solid for both organic ligands and corresponding U-MOFs highly correlates with the twisting of the branches, and both the anchoring of organic units and the construction of U-MOFs would be effective tools to modulate the trade-off between twisting and rotation, and that rotation could play a key role in promoting a turn-on antenna effect. • The relationship between twisting and rotation is disclosed in U-MOFs • Adjusting steric hindrance gives a trade-off between twisting and rotation • Luminescence in U-MOFs is fine-tuned by twisting the branches • Rotation could play a key role in turn-on antenna effect Twisting and rotation of organic linkers co-exist in the solid state of metal-organic frameworks, one increasing luminescence and the other decreasing luminescence. Yin et al. find that steric hinderance and coordination of uranyl ions can control the twisting of branches of organic building blocks, offering good trade-off between twisting and rotation.

Substrate-Modulated Synthesis of Metal-Organic Hybrids by Tunable Multiple Aryl-Metal Bonds.

Assembly of semiconducting organic molecules with multiple aryl-metal covalent bonds into stable one- and two-dimensional (1D and 2D) metal-organic frameworks represents a promising route to the integration of single-molecule electronics in terms of structural robustness and charge transport efficiency. Although various metastable organometallic frameworks have been constructed by the extensive use of single aryl-metal bonds, it remains a great challenge to embed multiple aryl-metal bonds into these structures due to inadequate knowledge of harnessing such complex bonding motifs. Here, we demonstrate the substrate-modulated synthesis of 1D and 2D metal-organic hybrids (MOHs) with the organic building blocks (perylene) interlinked solely with multiple aryl-metal bonds via the stepwise thermal dehalogenation of 3,4,9,10-tetrabromo-1,6,7,12-tetrachloroperylene and subsequent metal-organic connection on metal surfaces. More importantly, the conversion from 1D to 2D MOHs is completely impeded on Au(111) but dominant on Ag(111). We comprehensively study the distinct reaction pathways on the two surfaces by visually tracking the structural evolution of the MOHs with high-resolution scanning tunneling and noncontact atomic force microscopy, supported by first-principles density functional theory calculations. The substrate-dependent structural control of the MOHs is attributed to the variation of the M-X (M = Au, Ag; X = C, Cl) bond strength regulated by the nature of the metal species.

A 2D perchlorinated sp2-carbon framework

Two-dimensional (2D) π-conjugated polymers are promising electronic materials with diverse properties controlled by varying the structure of organic building blocks. We here report an organic framework with perchlorotriphenylmethyl (PTM) radical nodes, synthesized through dehalogenative thermolysis polymerization of tris(iodotetrachlorophenyl)methane. The resulting C-C-linked P2PTM is characterized by X-ray photoelectron, NMR, Raman, and FTIR spectroscopies and X-ray diffraction. Exfoliated, layered 2D sheets can be imaged with TEM and AFM. N2 adsorption experiment indicates a permanent porosity with a surface area of 150 m2/g, and dynamic vapor sorption shows a specific adsorption of one chloroform molecule per P2PTM unit cell, in line with modeling. DFT calculations predict degenerate Mott-insulating antiferromagnetic and ferromagnetic states, while the semi-metallic closed-shell configuration is less stable by ∼1 eV. Experimentally, P2PTM is a low-bandgap black solid with moderate electrical conductivity (∼4 × 10−4 S cm−1), gate-modulated ambipolar charge transport and paramagnetic behavior down to 1.9 K.

Exovinylene Cyclic Carbonates: Multifaceted CO2‐Based Building Blocks for Modern Chemistry and Polymer Science

AbstractCarbon dioxide is a renewable, inexhaustible, and cheap alternative to fossil resources for the production of fine chemicals and plastics. It can notably be converted into exovinylene cyclic carbonates, unique synthons gaining momentum for the preparation of an impressive range of important organic molecules and functional polymers, in reactions proceeding with 100 % atom economy under mild operating conditions in most cases. This Review summarizes the recent advances in their synthesis with particular attention on describing the catalysts needed for their preparation and discussing the unique reactivity of these CO2‐based heterocycles for the construction of diverse organic building blocks and (functional) polymers. We also discuss the challenges and the future perspectives in the field.

Exovinylene Cyclic Carbonates: Multifaceted CO2 -Based Building Blocks for Modern Chemistry and Polymer Science.

Carbon dioxide is a renewable, inexhaustible, and cheap alternative to fossil resources for the production of fine chemicals and plastics. It can notably be converted into exovinylene cyclic carbonates, unique synthons gaining momentum for the preparation of an impressive range of important organic molecules and functional polymers, in reactions proceeding with 100 % atom economy under mild operating conditions in most cases. This Review summarizes the recent advances in their synthesis with particular attention on describing the catalysts needed for their preparation and discussing the unique reactivity of these CO2 -based heterocycles for the construction of diverse organic building blocks and (functional) polymers. We also discuss the challenges and the future perspectives in the field.

Rapid fabrication of fluorinated covalent organic polymer membranes for organic solvent nanofiltration

Covalent organic polymers (COPs) are prepared via the non-uniform covalent assembly of organic building blocks, endowing their structures with permanent pores, thereby rendering them suitable for diverse applications. The use of COPs in the fabrication of composite membranes can enhance their permeability, selectivity, and chemical stability. However, the existing COP synthesis processes are typically tedious, thus necessitating the development of rapid and simpler routes. We demonstrate an easily performed synthesis route for the rapid (less than 10 s) fabrication of COP-based composite membranes via interfacial polymerization. The membranes were directly prepared on a polyacrylonitrile substrate without transferring the COP layer onto a porous support. The hydrophobicity of the membranes was achieved by the integration of fluorine-rich groups along the polymer backbone. The obtained solvent-resistant composite membranes exhibited a toluene permeance of 11 L m −2 h −1 bar −1 and congo red (687 g mol −1 ) rejection levels of more than 95%. The remarkable performance, crosslinked polymer structure, and manufacturing scalability of the fabricated thin films make them attractive as solvent-resistant nanofiltration membranes. Ultrafast fabrication of covalent organic polymer composite membranes for high-permeance nanofiltration in toluene. • Rapid synthesis of covalent organic polymer (COP) membrane via interfacial polymerization • Hydrophobicity of COP by integrating fluorine atoms • Hydrophobic pathways for highly selective organic solvent permeance • COP membranes with excellent toluene permeance and high dye rejections • Solvent-stable COP thin films with long-term stability during organic solvent nanofiltration

Hypercrosslinked Polymer Gels as a Synthetic Hybridization Platform for Designing Versatile Molecular Separators.

Hypercrosslinked polymers (HCPs), amorphous microporous three-dimensional networks based on covalent linkage of organic building blocks, are a promising class of materials due to their high surface area and easy functionalization; however, this type of material lacks processability due to its network rigidity based on covalent crosslinking. Indeed, the development of strategies to improve its solution processability for broader applications remains challenging. Although HCPs have similar three-dimensionally crosslinked networks to polymer gels, HCPs usually do not form gels but insoluble powders. Herein, we report the synthesis of HCP gels from a thermally induced polymerization of a tetrahedral monomer, which undergoes consecutive solubilization, covalent bond formation, colloidal formation, followed by their aggregation and percolation to yield a hierarchically porous network. The resulting gels feature concentration-dependent hierarchical porosities and mechanical stiffness. Furthermore, these HCP gels can be used as a platform to achieve molecular-level hybridization with a two-dimensional polymer during the HCP gel formation. This method provides functional gels and corresponding aerogels with the enhancement of porosities and mechanical stiffness. Used in column- and membrane-based molecular separation systems, the hybrid gels exhibited a separation of water contaminants with the efficiency of 97.9 and 98.6% for methylene blue and KMnO4, respectively. This result demonstrated the potentials of the HCP gels and their hybrid derivatives in separation systems requiring macroscopic scaffolds with hierarchical porosity.

Covalent Organic Frameworks (COFS): A Review

The search for supramolecular promising porous crystalline materials with diverse applications such as gas storage, catalysis, chemo-sensing, energy storage, and optoelectronic have led to the design and construction of Covalent Organic Frameworks (COFs). COFs are a class of porous crystalline polymers that allow the precise integration of organic building blocks and linkage motifs to create predesigned skeletons and nano-porous materials. In this review article, a historic overview of the chemistry of COFs, survey of the advances in topology design and synthetic reactions, basic design principles that govern the formation of COFs as porous crystalline polymers as well as common synthetic procedures and characterization techniques are discussed. Furthermore some challenges associate with the synthesis of COFs are highlighted. We hope that this review will help researchers, industrialists and academics in no mean feat.

Imine-linked porous aromatic frameworks based on spirobifluorene building blocks for CO2 separation

Porous organic frameworks entirely composed of organic building blocks are attracting more and more attention owing to their tunable porosity, lightweight and hydrolytic stability. Three novel porous aromatic frameworks (PAFs) based on the [4 + 3] design strategy have been synthesized from spirobifluorene building block as square node and various triangle nodes respectively via imine condensation. These materials are all semiconductors and permanently microporous amorphous polymer with high thermal stabilities. The Brunauer-Emmett-Teller (BET) surface areas of these PAFs are between 389 and 698 m 2 /g. More importantly, these frameworks exhibit good CO 2 uptake (4.0 mmol/g for PAF-131) and outstanding ideal adsorption selectivities for CO 2 /N 2 (121 for PAF-131) and CO 2 /CH 4 (327 for PAF-131) at 273 K and 1 bar, thus showing that they are good candidates for CO 2 capture. • Spirobifluorene-based porous aromatic frameworks formed by imine condensation. • Frameworks constructed from [4 + 3] networks of square and triangle nodes. • Materials with semiconductive character and permanently microporosity. • High CO 2 uptake and outstanding adsorption selectivities for CO 2 /N 2 and CO 2 /CH 4 .

Creating Optimal Pockets in a Clathrochelate-Based Metal-Organic Framework for Gas Adsorption and Separation: Experimental and Computational Studies.

The rational design and synthesis of robust metal-organic frameworks (MOFs) based on novel organic building blocks are fundamental aspects of reticular chemistry. Beyond simply fabricating new organic linkers, however, it is important to elucidate structure-property relationships at the molecular level to develop high-performing materials. In this work, we successfully targeted a highly porous and robust cage-type MOF (NU-200) with an nbo-derived fof topology through the deliberate assembly of a cyclohexane-functionalized iron(II)-clathrochelate-based meta-benzenedicarboxylate linker with a Cu2(CO2)4 secondary building unit (SBU). NU-200 exhibited an outstanding adsorption capacity of xenon and a high ideal adsorbed solution theory (IAST) predicted selectivity for a 20/80 v/v mixture of xenon (Xe)/krypton (Kr) at 298 K and 1.0 bar. Our extensive computational simulations with grand canonical Monte Carlo (GCMC) and density functional theory (DFT) on NU-200 indicated that the MOF's hierarchical bowl-shaped nanopockets surrounded by custom-designed cyclohexyl groups─instead of the conventionally believed open metal sites (OMSs)─played a crucial role in reinforcing Xe-binding affinity. The optimally sized pockets firmly trapped Xe through numerous supramolecular interactions including Xe···H, Xe···O, and Xe···π. Additionally, we validated the unique pocket confinement effect by experimentally and computationally employing the similarly sized probe, sulfur dioxide (SO2), which provided significant insights into the molecular underpinnings of the high uptake of SO2 (11.7 mmol g-1), especially at a low pressure of 0.1 bar (8.5 mmol g-1). This work therefore can facilitate the judicious design of organic building blocks, producing MOFs featuring tailor-made pockets to boost gas adsorption and separation performances.

Synthesis of Vinylene-Linked Covalent Organic Frameworks by Monomer Self-Catalyzed Activation of Knoevenagel Condensation.

Reticular chemistry based on thermodynamically controlled linking modes and numerous organic building blocks has constituted versatile crystalline frameworks in molecular-level precision. However, vinylene-linked covalent organic frameworks (COFs) are still quite far from flexible tailoring in either their structures or topologies, due to the lack of monomers with sufficient activities. Herein, we establish a strategy to synthesize vinylene-linked COFs via Knoevenagel condensation between a tetratopic monomer 2,2',6,6'-tetramethyl-4,4'-bipyridine (TMBP) and linear aromatic dialdehydes in a mixed solvent of benzoic anhydride and benzoic acid. Mechanistic investigation suggests that the condensation was promoted by a pyridine self-catalyzed benzoylation upon the cleavage of benzoic anhydride solvent molecules. The layered structures of the resultant COFs are highly crystallized into orthorhombic lattices with vertically aligned AA stacking modes, delivering high surface areas up to 1560 m2 g-1. The π-extended conjugated skeletons comprising para-bipyridyl units and vinylene linkages endow these COFs with substantial semiconducting properties, releasing visible-light-stimulated catalytic activity in water-splitting hydrogen evolution with a rate as high as 3230 μmol g-1 h-1.

An Adaptive Hydrogen-Bonded Organic Framework for the Exclusive Recognition of p-Xylene.

Separation of xylene isomers is one of the most important but most challenging and energy-intensive separation processes in the petrochemical industry. Here, we report an adaptive hydrogen-bonded organic framework (HOF-29) constructed from a porphyrin based organic building block 4,4',4'',4'''-(porphyrin-5,10,15,20-tetrayl) tetrabenzonitrile (PTTBN), exhibiting the exclusive molecular recognition of p-xylene (pX) over its isomers of o-xylene (oX) and m-xylene (mX), as clearly demonstrated in the single crystal structure transformation and 1 H NMR studies. Single crystal structure studies show that single-crystal-to-single-crystal transformation from the as-synthesized HOF-29 to the pX exclusively included HOF-29⊃pX is triggered by the encapsulation of pX molecules, accompanied by sliding of the 2D layers and local distortion of the ligand, which provides multiple C-H⋅⋅⋅π interactions.

Tailoring Anchoring Groups in Low‐Dimensional Organic Semiconductor‐Incorporated Perovskites

Low‐dimensional, organic semiconductor‐incorporated perovskites (OSiPs) are hybrid structures with functional organic cations intercalated between inorganic octahedron frameworks. They exhibit increased structural and compositional tunability, fascinating electronic properties, and enhanced stability for a wide range of applications. Currently, the interactions between the conjugated organic building blocks and the metal halide inorganic building blocks have not been fully investigated. Herein, a series of bithiophene‐based conjugated ligands with formamidinium, imidazolium, and benzimidazolium terminal groups to examine the influence of different anchoring groups on the crystal structures, phase formation, and device performances are reported. It is shown that the terminal groups of the ligands have significant effect on the interactions between ligands and octahedra in perovskites, thus determine the formation of the crystal structures. Only the 3D perovskite solar cells passivated by the ligands with imidazolium and benzimidazolium terminal groups exhibit enhancement in power conversion efficiencies as well as reduced hysteresis. A new strategy is provided for designing novel OSiPs structures and functionalities via tailoring the anchoring group.

Controlled Crystallization of Diblock Copolymers on Carbon materials: Effect of Block Length

The fabrication of sophisticated hybrid mesostructures involving carbon nanomaterials and organic building blocks has attracted great attention due to their tunable properties and potential applications. Herein, we report the precisely controlled structure and morphology of diblock copolymers-carbon materials hybrid mesostructures, in which nano/micron- disc shape and honeycomb structure were fabricated on the surfaces of carbon nanotube (CNT), carbon nanofiber (CNF), and graphite, respectively. Synthesized ethylene/functional cyclic olefin block copolymers (PE-b-HPNBMA) showed a narrow dispersity, allowing the formation of nanohybrid shish-kebab structures (NHSK) with a highly uniform disc-shape crystalline size and period. The tunability of HPNBMA block length and functional substituent enables not only control of the nanocrystal size but also flexible design of the surface chemical structure, which can endow diblock copolymers-carbon materials hybrid mesostructures with specific properties. As proof of the ability, superhydrophobic (contact angle > 150°) NHSK films with tunable adhesion were successfully produced.

Olefin-linked covalent organic framework nanotubes based on triazine for selective oxidation of sulfides with O2 powered by blue light

Imine, hydrazone, and olefin-linked covalent organic frameworks (COFs) prosper in visible light photocatalysis. Markedly, the olefin-linked COFs are usually superior in transfer of π-conjugated electron powered by visible light albeit their construction is more challenging. Herein, two olefin-linked COFs were forged between 2,4,6-trimethyl-1,3,5-triazine (TMT) and 2,4,6-tris(4-formyl-phenyl)-1,3,5-triazine (TFPT) or 1,3,5-tris(4-formyl-phenyl)-benzene (TFPB) to afford TTO-COF or TBO-COF, respectively. Both of the olefin-linked COFs based on triazine are of good crystallinity, uniform micropores, and high specific surface areas, but of different morphologies, namely nanotubes and nanosheets. Compared to TBO-COF, TTO-COF nanotubes were constructed with two building blocks based on triazine, which could not only improve the planarity of a single layer but also cause closer stacking of layers in between. Therefore, TTO-COF nanotubes exhibit better photocatalytic performance and stability in the selective oxidation of organic sulfides into corresponding sulfoxides with O2 powered by blue light. Mechanistic investigation evidence the formation of desired sulfoxides was shaped by both electron and energy transfer pathways over TTO-COF nanotubes. This work underlines the ascendancy of olefin-linked COFs inasmuch as they provide an effective platform to construct efficient and durable photocatalysts based on adaptable organic building blocks.

Coordination Cage-Based Emulsifiers: Templated Formation of Metal Oxide Microcapsules Monitored by In Situ LC-TEM.

Metallo‐supramolecular self‐assembly has yielded a plethora of discrete nanosystems, many of which show competence in capturing guests and catalyzing chemical reactions. However, the potential of low‐molecular bottom‐up self‐assemblies in the development of structured inorganic materials has rarely been methodically explored so far. Herein, we present a new type of metallo‐supramolecular surfactant with the ability to stabilize non‐aqueous emulsions for a significant period. The molecular design of the surfactant is based on a heteroleptic coordination cage (CGA‐3; CGA=Cage‐based Gemini Amphiphile), assembled from two pairs of organic building blocks, grouped around two Pd(II) cations. Shape‐complementarity between the differently functionalized components generates discrete amphiphiles with a tailor‐made polarity profile, able to stabilize non‐aqueous emulsions, such as hexadecane‐in‐DMSO. These emulsions were used as a medium for the synthesis of spherical metal oxide microcapsules (titanium oxide, zirconium oxide, and niobium oxide) from soluble, water‐sensitive alkoxide precursors by allowing a controlled dosage of water to the liquid‐liquid phase boundary. Synthesized materials were analyzed by a combination of electron microscopic techniques. In situ liquid cell transmission electron microscopy (LC‐TEM) was utilized for the first time to visualize the dynamics of the emulsion‐templated formation of hollow inorganic titanium oxide and zirconium oxide microspheres.

Ultrafast Aggregation-Induced Tunable Emission Enhancement in a Benzothiadiazole-Based Fluorescent Metal-Organic Framework Linker.

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.

Organic/Inorganic Self-Assembled Hybrid Nano-Architectures for Cancer Therapy Applications.

Since the conceptualization of nanomedicine, numerous nanostructure-mediated drug formulations have progressed into clinical trials for treating cancer. However, recent clinical trial results indicate such kind of drug formulations has a limited improvement on the antitumor efficacy. This is due to the biological barriers associated with those formulations, for example, circulation stability, extravasation efficiency in tumor, tumor penetration ability, and developed multi-drug resistance. When employing for nanomedicine formulations, pristine organic-based and inorganic-based nanostructures have their own limitations. Accordingly, organic/inorganic (O/I) hybrids have been developed to integrate the merits of both, and to minimize their intrinsic drawbacks. In this context, the recent development in O/I hybrids resulting from a self-assembly strategy will be introduced. Through such a strategy, organic and inorganic building blocks can be self-assembled via either chemical covalent bonds or physical interactions. Based on the self-assemble procedure, the hybridization of four organic building blocks including liposomes, micelles, dendrimers, and polymeric nanocapsules with five functional inorganic nanoparticles comprising gold nanostructures, magnetic nanoparticles, carbon-based materials, quantum dots, and silica nanoparticles will be highlighted. The recent progress of these O/I hybrids in advanced modalities for combating cancer, such as, therapeutic agent delivery, photothermal therapy, photodynamic therapy, and immunotherapy will be systematically reviewed.

Crosslinked copolystyrenes based membranes bearing alkylcarboxylated and alkylsulfonated side chains for organic solvent nanofiltration

Polymeric membranes are more practicable to the cost-effective and energy-efficient solvent recovery and molecular separation in solvent mixtures, but the construction of structure-defined chemically stable as well as high permeance polymer membranes for organic solvent nanofiltration (OSN) applications is an important challenge. Herein, we designed and constructed crosslinked block copolystyrene membranes containing flexible alkylcarboxylated and alkylsufonated side chains for high-separation performance in organic media. The flexible side chains anchored on the all-carbon network render the membranes with good dimensional flexibility due to the rational manipulation of the intermolecular and intramolecular bonding interactions within the crosslinked structured polymer chains. Depending on the crosslinking degree, the resultant membranes exhibited outstanding stability in polar protic solvents, mild polar aprotic solvents (THF, acetonitrile and acetone) and nonpolar solvents. Specifically, the CPS-24% membrane with a cutoff of 380 g mol−1 showed good ethanol permeance of 4.16 L m−2 h−1 bar−1 and a high-efficient molecular separation (>96%) of a broad range of small molecular weight solutes (organic dye molecules, organic building blocks and antibiotics). The membrane also achieved molecular level selectivity of two molecules with a mass difference down to 141 g mol−1, which is attractive for molecular separation in the chemical and pharmaceutical industry. This work provides a promising strategy to improve selective solvent permeation and separation of organic molecules in OSN membranes by introducing flexible hydrophilic/hydrophobic side chain domains into the main backbone of rigid polymer structures.