3D COFs Research Articles

Confinement-Driven Enantioselectivity in 3D Porous Chiral Covalent Organic Frameworks.

3D covalent organic frameworks (COFs) with well-defined porous channels are shown to be capable of inducing chiral molecular catalysts from non-enantioselective to highly enantioselective in catalyzing organic transformations. By condensations of a tetrahedral tetraamine and two linear dialdehydes derived from enantiopure 1,1'-binaphthol (BINOL), two chiral 3D COFs with a 9-fold or 11-fold interpenetrated diamondoid framework are prepared. Enhanced Brønsted acidity was observed for the chiral BINOL units that are uniformly distributed within the tubular channels compared to the non-immobilized acids. This facilitates the Brønsted acid catalysis of cyclocondensation of aldehydes and anthranilamides to produce 2,3-dihydroquinazolinones. DFT calculations show the COF catalyst provides preferential secondary interactions between the substrate and framework to induce enantioselectivities that are not achievable in homogeneous systems.

A Crystalline Three-Dimensional Covalent Organic Framework with Flexible Building Blocks.

The construction of three-dimensional covalent organic frameworks (3D COFs) has proven to be very challenging, as their synthetic driving force mainly comes from the formation of covalent bonds. To facilitate the synthesis, rigid building blocks are always the first choice for designing 3D COFs. In principle, it should be very appealing to construct 3D COFs from flexible building blocks, but there are some obstacles blocking the development of such systems, especially for the designed synthesis and structure determination. Herein, we reported a novel highly crystalline 3D COF (FCOF-5) with flexible C-O single bonds in the building block backbone. By merging 17 continuous rotation electron diffraction data sets, we successfully determined the crystal structure of FCOF-5 to be a 6-fold interpenetrated pts topology. Interestingly, FCOF-5 is flexible and can undergo reversible expansion/contraction upon vapor adsorption/desorption, indicating a breathing motion. Moreover, a smart soft polymer composite film with FCOF-5 was fabricated, which can show a reversible vapor-triggered shape transformation. Therefore, 3D COFs constructed from flexible building blocks can exhibit interesting breathing behavior, and finally, a totally new type of soft porous crystals made of pure organic framework was announced.

3D Covalent Organic Frameworks Based on Polycyclic Aromatic Hydrocarbons for Reversible Oxygen Capture

Singlet oxygen, as a kind of reactive oxygen species, plays an important role in organic synthesis and biological processes. However, these excited oxygen molecules have a short life and high reactivity; thus it is a great challenge to capture singlet oxygen. Here, for the first time two functionalized 3D covalent organic frameworks (3D COFs) with polycyclic aromatic hydrocarbons, termed as JUC‐575 and JUC‐576, for reversible singlet oxygen capture and release are reported. These 3D COFs, constructed from anthracene or naphthalene derivatives, can effectively trap singlet oxygen through chemical transformation to generate the corresponding endoperoxide COFs (EPO‐COFs). Furthermore, it is also confirmed that the reversible oxygen capture and release between the parent COFs and EPO‐COFs can be well controlled by switching the UV–vis irradiation. This study thus broadens the potential applications of 3D functionalized COFs as molecular carriers in biology and organic synthesis.

Triptycene-based three-dimensional covalent organic frameworks with stp topology of honeycomb structure

Two triptycene based 3D COFs with stp topology and the “6 + 4” linking mode was synthesized. The 3D COFs exhibit honeycomb nanochannels structures with different pore sizes according to different linkages.

Engineering COFs as smart triggers for rapid capture and controlled release of singlet oxygen

A new 3-dimensional covalent organic framework (3D COF) with a 4-fold interpenetrated dia topology was fabricated, which exhibited outstanding 1O2 capture performance and demonstrated potential anti-fake applications.

Facile synthesis of 3D covalent organic frameworks via a two-in-one strategy.

A "two-in-one" strategy was employed to construct 3D-COFs for the first time. Based on this strategy, a 3D-Flu-COF could be readily synthesized in various simplex organic solvents. Benefitting from the non-conjugated structure, the 3D-Flu-COF showcased excellent acidichromic sensing performance with good sensitivity, reversibility and naked eye visibility.

Three-dimensional covalent organic frameworks based on a π-conjugated tetrahedral node

Three fully conjugated 3D COFs with dia and pts topologies have been constructed from saddle-like cyclooctatetrathiophene (COTh) as π-conjugated tetrahedral node.

Three-dimensional covalent organic framework membrane for efficient proton conduction

A free-standing 3D COF membrane with interconnected nanochannels was fabricated using interfacial polymerization method, and exhibited ultrafast proton conduction after being loaded with proton carriers.

Three‐Dimensional Covalent‐Organic Frameworks Loaded with Highly Dispersed Ultrafine Palladium Nanoparticles as Efficient Heterogeneous Catalyst

AbstractIn this work, we exploited the notable advantages of using three‐dimensional covalent organic frameworks (3D COFs) as supports for efficiently and controllably loading Pd. Tetraphenylmethane based 3D COF (TPM‐3D‐COF‐BPY) bearing bipyridine as coordination sites was constructed. A 7‐fold interpenetrated dia structure was revealed by the aid of powder X‐ray diffraction (PXRD) and structural simulation. The unique side‐by‐side 1D channels of TPM‐3D‐COF‐BPY provide enormous easily accessible active surface areas for heterogeneous catalysis throughout the topological structure. The delicate 7‐fold interpenetration of the bipyridine linked frameworks yields discrete and widespread coordination sites and enables super‐efficient heterogeneous catalysis after metalation of nitrogen coordination sites in TPM‐3D‐COF‐BPY. As a demonstration, Pd(II) was selectively anchored to the bipyridine coordination sites in the TPM‐3D‐COF‐BPY matrix. Further reduction of Pd(II) loaded in the topological structure leads to highly dispersed ultrafine Pd nanoparticles (NPs) with an average size of 1.12 nm confined within channels of TPM‐3D‐COF‐BPY. The as‐prepared Pd@TPM‐3D‐COF‐BPY as heterogeneous catalyst exhibits excellent efficiency, stability, and recyclability in catalyzing the Suziki‐Miyaura coupling reactions reaching a 98% yield within 2 h under facile conditions.

Structural Dynamism-Actuated Reversible CO2 Adsorption Switch and Postmetalation-Induced Visible Light Cα-H Photocyanation with Rare Size Selectivity in N-Functionalized 3D Covalent Organic Framework.

The impact of dimensionality and flexibility on anticipated properties has prompted major research focus to three-dimensional covalent organic frameworks (3D COFs), where astute functionalization of porous channels for dynamic CO2 adsorption as well as size-exclusive C-H activation under eco-friendly condition are the most intriguing advanced applications. Herein, we report an imine-based, diamondoid COF that embraces one-dimensional porous channels in spite of ninefold interpenetration. A combination of intrinsic microporosity and pore wall decoration with accessible N atoms from linear strut renders this 3D COF display reasonable CO2 affinity with decent selectivity (CO2/N2: 64.2; CO2/CH4: 10.5) alongside worthy multicyclic CO2 uptake-release recurrence. Interestingly, the COF undergoes solvent-assisted alteration to a pore-stretched structure via -C═N- "pedal" motion with a concomitant enhancement in CO2 uptake, where steady reversibility of such structural dynamism instigates unprecedented CO2 adsorption switch up to seven consecutive cycles. Integration of 2,2'-bipyridyl units benefits anchoring of homogeneous catalyst to device first-ever Ru(Bpy)22+ hooked diamondoid COF (Ru-COF), which performs visible-light-triggered oxidative cyanation of tertiary amines at room temperature, using molecular oxygen as a selective oxidant in green solvent H2O. The photocatalyst-engineered COF manifests excellent recyclability and comparable activity to that of homogeneous catalyst. To the best of Ru-COF, atom-economic photocyanation is realized via in situ generated iminium ion, wherein larger-sized substrates exhibit insignificant conversion of α-aminonitriles and validate rarest size selectivity in oxidative Strecker reaction. This study not only demonstrates potential of 3D COF as next-generation dynamic CO2 adsorbent but also sheds light on tailor-made fabrication of smart functional material for promising catalytic applications through an environmentally benign route.

Redox-triggered switching in three-dimensional covalent organic frameworks

The tuning of molecular switches in solid state toward stimuli-responsive materials has attracted more and more attention in recent years. Herein, we report a switchable three-dimensional covalent organic framework (3D COF), which can undergo a reversible transformation through a hydroquinone/quinone redox reaction while retaining the crystallinity and porosity. Our results clearly show that the switching process gradually happened through the COF framework, with an almost quantitative conversion yield. In addition, the redox-triggered transformation will form different functional groups on the pore surface and modify the shape of pore channel, which can result in tunable gas separation property. This study strongly demonstrates 3D COFs can provide robust platforms for efficient tuning of molecular switches in solid state. More importantly, switching of these moieties in 3D COFs can remarkably modify the internal pore environment, which will thus enable the resulting materials with interesting stimuli-responsive properties.

In situ fabrication of 3D COF-300 in a capillary for separation of aromatic compounds by open-tubular capillary electrochromatography

Two-dimensional (2D) COFs have been successfully applied for various applications, such as capillary electrochromatography (CEC). Compared with 2D COFs, three-dimensional (3D) COFs have higher surface area and lower density, which should have superior potential as the separation medium in CEC. However, the 3D COFs on the inner wall of capillary is hard to fabricate in situ. Up to date, the application of 3D COFs in open-tubular capillary electrochromatography (OT-CEC) is still considered a challenge. For the first timethe COF-300-coated capillary was prepared by in situ growth (COF-300 was made from terephthalaldehyde and tetra-(4-anilyl)-methane) on OT-CEC. Benzene, methylbenzene, styrene, ethylbenzene, naphthalene, 1-methylnaphthalene, and propylbenzene were used to evaluate the performance of the COF-300-coated capillary by OT-CEC. For three consecutive runs, the intraday relative standard deviations (RSDs) of migration time and peak areas were 0.1-0.4% and 2.5-8.3%, respectively. The interday RSDs of migration time and peak areas were 0.2-0.5% and 1.0-10.8%, respectively. Five groups of aromatic co mpounds were used to further study the separation mechanism, which indicated that hydrophobic interaction and size selection interaction are the main factors. It should be noted that the COF-300-coated capillary can be used for more than 140 runs with no observable changes ofthe separation efficiency. Graphical abstract The 3D COF-300-coated capillary was prepared by in situ growth for OT-CEC. Six groups of aromatic compounds were separated by 3D COF-300-coated capillary. Size selection and hydrophobic interaction affect the migration time of analytes.

Syntheses of two- and three-dimensional covalent organic frameworks in deep eutectic solvents

For the first time, a mild and green strategy is reported for the efficient syntheses of a series of 2D and 3D COFs using deep eutectic solvents as clean media under ambient conditions.

Isostructural Three-Dimensional Covalent Organic Frameworks.

Herein, we reported the designed synthesis of three isostructural three-dimensional covalent organic frameworks (3D COFs) with -H, -Me, or -F substituents, which have similar crystallinity and topology. Their crystal structures were determined by continuous rotation electron diffraction (cRED), and all three 3D COFs were found to adopt a fivefold interpenetrated pts topology. More importantly, the resolution of these cRED datasets reached up to 0.9-1.0 Å, enabling the localization of all non-hydrogen atomic positions in a COF framework directly by 3D ED techniques for the first time. In addition, the precise control of the pore environments through the use of different functional groups led to different selectivities for CO2 over N2 . We have thus confirmed that polycrystalline COFs can be definitely studied to the atomic level as other materials, and this study should also inspire the design and synthesis of 3D COFs with tailored pore environments for interesting applications.

Isostructural Three‐Dimensional Covalent Organic Frameworks

AbstractHerein, we reported the designed synthesis of three isostructural three‐dimensional covalent organic frameworks (3D COFs) with ‐H, ‐Me, or ‐F substituents, which have similar crystallinity and topology. Their crystal structures were determined by continuous rotation electron diffraction (cRED), and all three 3D COFs were found to adopt a fivefold interpenetrated pts topology. More importantly, the resolution of these cRED datasets reached up to 0.9–1.0 Å, enabling the localization of all non‐hydrogen atomic positions in a COF framework directly by 3D ED techniques for the first time. In addition, the precise control of the pore environments through the use of different functional groups led to different selectivities for CO2 over N2. We have thus confirmed that polycrystalline COFs can be definitely studied to the atomic level as other materials, and this study should also inspire the design and synthesis of 3D COFs with tailored pore environments for interesting applications.

Cage Based Crystalline Covalent Organic Frameworks

The first two cage based crystalline covalent organic frameworks, cage-COF-1 and cage-COF-2, were constructed from a prism-like three-aldehyde-containing molecular cage. The cage contains two horizontal phloroglucinol and three vertical triazine moieties forming three identical V-shaped cavities. By reacting with p-phenylenediamine and 4,4'-biphenyldiamine, the two cage-COFs were formed with a hexagonal skeleton and possess a unique structure. Due to the pillared cage nodes, the linkers are hanging with their π-surfaces but not C-H sites exposed to the pore, and enjoy certain rotational dynamics as suggested by 13C CP/MAS NMR. The antidirection of the diimine linkages leads to rippled layers which pack in unique ABC mode through alternate stacking of the cage twosided faces in both AB and AC layers. Such packing forms trigonal channels along c axis which are interconnected in ab plane due to the large open space created across the hanging linkers, resembling the porous characteristics of 3D COFs. The cage-COFs have a permanent porosity and can adsorb CO2 facilitated by the intrinsic cage cavities that serve as prime adsorption sites. The unprecedented cage-COFs not only merge the borderline of 2D and 3D COFs but also bridge porous organic cages to extended crystalline organic frameworks.

Controlling the crystalline structure of imine-linked 3D covalent organic frameworks.

We explore the growth mechanism of 3D Covalent Organic Frameworks (COFs) using imine-linked model systems. We confirm that 3D imine COFs crystalize through an amorphous polymer intermediate, whose conditional state is key for preferential generation of the ideal porous structure over the collapsed hydrated form.

An AIEgen-based 3D covalent organic framework for white light-emitting diodes

The design and synthesis of three-dimensional covalent organic frameworks (3D COFs) have still been considered as a big challenge. Here we report the design and synthesis of an AIEgen-based 3D COF (3D-TPE-COF), with a high surface area (1084 m2 g−1). According to powder X-ray diffraction and continuous rotation electron diffraction analyses, 3D-TPE-COF is identified to adopt a seven-fold interpenetrated pts topology. Interestingly, 3D-TPE-COF emits yellow fluorescence upon excitation, with a photoluminescence quantum yield of 20%. Moreover, by simply coating 3D-TPE-COF onto a commercial blue light-emitting diode (LED), a prototype white LED (WLED) under continuously driving without degradation for 1200 h was demonstrated. The present work suggests the possibility of using COF materials for stable WLEDs, which will greatly inspire us to design and synthesize fluorescent 3D COFs and facilitate the development of COF-based WLEDs in future.

Highly Conjugated Three-Dimensional Covalent Organic Frameworks Based on Spirobifluorene for Perovskite Solar Cell Enhancement.

Highly conjugated three-dimensional covalent organic frameworks (3D COFs) were constructed based on spirobifluorene cores linked via imine bonds (SP-3D-COFs) with novel interlacing conjugation systems. The crystalline structures were confirmed by powder X-ray diffraction and detailed structural simulation. A 6- or 7-fold interpenetration was formed depending on the structure of the linking units. The obtained SP-3D-COFs showed permanent porosity and high thermal stability. In application for solar cells, simple bulk doping of SP-3D-COFs to the perovskite solar cells (PSCs) substantially improved the average power conversion efficiency by 15.9% for SP-3D-COF 1 and 18.0% for SP-3D-COF 2 as compared to the reference undoped PSC, while offering excellent leakage prevention in the meantime. By aid of both experimental and computational studies, a possible photoresponsive perovskite-SP-3D-COFs interaction mechanism was proposed to explain the improvement of PSC performance after SP-3D-COFs doping.

Three-Dimensional Anionic Cyclodextrin-Based Covalent Organic Frameworks.

Three-dimensional covalent organic frameworks (3D COFs) are promising crystalline materials with well-defined structures, high porosity, and low density; however, the limited choice of building blocks and synthetic difficulties have hampered their development. Herein, we used a flexible and aliphatic macrocycle, namely γ-cyclodextrin (γ-CD), as the soft struts for the construction of a polymeric and periodic 3D extended network, with the units joined via tetrakis(spiroborate) tetrahedra with various counterions. The inclusion of pliable moieties in the robust open framework endows these CD-COFs with dynamic features, leading to a prominent Li ion conductivity of up to 2.7 mS cm-1 at 30 °C and excellent long-term Li ion stripping/plating stability. Exchanging the counterions within the pores can effectively modulate the interactions between the CD-COF and CO2 molecules.