14 research outputs found
Porous covalent organic nanotubes and their assembly in loops and toroids
Carbon nanotubes, and synthetic organic nanotubes more generally, have in recent decades been widely explored for application in electronic devices, energy storage, catalysis and biosensors. Despite noteworthy progress made in the synthesis of nanotubular architectures with well-defined lengths and diameters, purely covalently bonded organic nanotubes have remained somewhat challenging to prepare. Here we report the synthesis of covalently bonded porous organic nanotubes (CONTs) by Schiff base reaction between a tetratopic amine-functionalized triptycene and a linear dialdehyde. The spatial orientation of the functional groups promotes the growth of the framework in one dimension, and the strong covalent bonds between carbon, nitrogen and oxygen impart the resulting CONTs with high thermal and chemical stability. Upon ultrasonication, the CONTs form intertwined structures that go on to coil and form toroidal superstructures. Computational studies give some insight into the effect of the solvent in this assembly process
Covalent Organic Frameworks as Porous Pigments for Photocatalytic Metal-Free C–H Borylation
Covalent organic frameworks (COFs) are highly promising
as heterogeneous
photocatalysts due to their tunable structures and optoelectronic
properties. Though COFs have been used as heterogeneous photocatalysts,
they have mainly been employed in water splitting, carbon dioxide
reduction, and hydrogen evolution reactions. A few examples in organic
synthesis using metal-anchored COF photocatalysts were reported. Herein,
we report highly stable β-keto-enamine-based COFs as photocatalysts
for metal-free C–B bond formation reactions. Three different
COFs have been availed for this purpose. Their photocatalysis performances
have been monitored for 12 different substrates, like quinolines,
pyridines, and pyrimidines. All the COFs showcase moderate-to-high
yields (up to 96%) depending upon the substrate’s molecular
functionality. High crystallinity, a large surface area, a low band
gap, and a suitable band position result in the highest catalytic
activity of TpAzo COF. The thorough mechanistic investigation further
highlights the crucial role of light-harvesting capacity, charge separation
efficiency, and current density during catalysis. The light absorbance
capacity of the COF plays a critical role during catalysis as yields
are maximized near the COF’s absorption maxima. The high photostability
of the as-synthesized COFs offers their reusability for several (>5)
catalytic cycles
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Interplaying anions in a supramolecular metallohydrogel to form metal organic frameworks
The remarkable effect of anions on the transition from supramolecular gels to crystalline phases has been described. An amino acid-based metallohydrogel was transformed into different metal-organic frameworks through the selective picking of anions. The metallohydrogel and the resulting metal-organic frameworks (MOFs) were thoroughly characterized. The results demonstrated controlled access over the binding of a particular anion to selectively form a particular MOF
A Covalent Organic Framework for Cooperative Water Oxidation
The future of water-derived hydrogen as the “sustainable energy source” straightaway bets on the success of the sluggish oxygen-generating half-reaction. The endeavor to emulate the natural photosystem II for efficient water oxidation has been extended across the spectrum of organic and inorganic combinations. However, the achievement has so far been restricted to homogeneous catalysts rather than their pristine heterogeneous forms. The poor structural understanding and control over the mechanistic pathway often impede the overall development. Herein, we have synthesized a highly crystalline covalent organic framework (COF) for chemical and photochemical water oxidation. The interpenetrated structure assures the catalyst stability, as the catalyst’s performance remains unaltered after several cycles. This COF exhibits the highest ever accomplished catalytic activity for such an organometallic crystalline solid-state material where the rate of oxygen evolution is as high as ∼26,000 μmol L s (second-order rate constant k ≈ 1650 μmol L s g). The catalyst also proves its exceptional activity (k ≈ 1600 μmol L s g) during light-driven water oxidation under very dilute conditions. The cooperative interaction between metal centers in the crystalline network offers 20–30-fold superior activity during chemical as well as photocatalytic water oxidation as compared to its amorphous polymeric counterpart
Bottom-Up Synthesis of Crystalline Covalent Organic Framework Nanosheets, Nanotubes, and Kippah Vesicles: An Odd-Even Effect Induction
Few-layer organic nanosheets are becoming increasingly attractive as two-dimensional (2D) materials due to their precise atomic connectivity and tailor-made pores. However, most strategies for synthesizing nanosheets rely on surface-assisted methods or top-down exfoliation of stacked materials. A bottom-up approach with well-designed building blocks would be the convenient pathway to achieve the bulk-scale synthesis of 2D nanosheets with uniform size and crystallinity. Herein, we have synthesized crystalline covalent organic framework nanosheets (CONs) by reacting tetratopic thianthrene tetraaldehyde (THT) and aliphatic diamines. The bent geometry of thianthrene in THT retards the out-of-plane stacking, while the flexible diamines introduce dynamic characteristics into the framework, facilitating nanosheet formation. Successful isoreticulation with five diamines with two to six carbon chain lengths generalizes the design strategy. Microscopic imaging reveals that the odd and even diamine-based CONs transmute to different nanostructures, such as nanotubes and hollow spheres. The single-crystal X-ray diffraction structure of repeating units indicates that the odd-even linker units of diamines introduce irregular-regular curvature in the backbone, aiding such dimensionality conversion. Theoretical calculations shed more light on nanosheet stacking and rolling behavior with respect to the odd-even effects.11Nsciescopu
A Covalent Organic Framework for Cooperative Water Oxidation
The future of water-derived hydrogen as the “sustainable
energy source” straightaway bets on the success of the sluggish
oxygen-generating half-reaction. The endeavor to emulate the natural
photosystem II for efficient water oxidation has been extended across
the spectrum of organic and inorganic combinations. However, the achievement
has so far been restricted to homogeneous catalysts rather than their
pristine heterogeneous forms. The poor structural understanding and
control over the mechanistic pathway often impede the overall development.
Herein, we have synthesized a highly crystalline covalent organic
framework (COF) for chemical and photochemical water oxidation. The
interpenetrated structure assures the catalyst stability, as the catalyst’s
performance remains unaltered after several cycles. This COF exhibits
the highest ever accomplished catalytic activity for such an organometallic
crystalline solid-state material where the rate of oxygen evolution
is as high as ∼26,000 μmol L–1 s–1 (second-order rate constant k ≈
1650 μmol L s–1 g–2). The
catalyst also proves its exceptional activity (k ≈
1600 μmol L s–1 g–2) during
light-driven water oxidation under very dilute conditions. The cooperative
interaction between metal centers in the crystalline network offers
20–30-fold superior activity during chemical as well as photocatalytic
water oxidation as compared to its amorphous polymeric counterpart