Using molecular straps to engineer conjugated porous polymer growth, chemical doping, and conductivity

Controlling network growth and architecture of 3D-conjugated porous polymers (CPPs) is challenging and therefore has limited the ability to systematically tune the network architecture and study its impact on doping efficiency and conductivity. We have proposed that π-face masking straps mask the π-face of the polymer backbone and therefore help to control π-π interchain interactions in higher dimensional π-conjugated materials unlike the conventional linear alkyl pendant solubilizing chains that are incapable of masking the π-face. Herein, we used cycloaraliphane-based π-face masking strapped monomers and show that the strapped repeat units, unlike the conventional monomers, help to overcome the strong interchain π-π interactions, extend network residence time, tune network growth, and increase chemical doping and conductivity in 3D-conjugated porous polymers. The straps doubled the network crosslinking density, which resulted in 18 times higher chemical doping efficiency compared to the control non-strapped-CPP. The straps also provided synthetic tunability and generated CPPs of varying network size, crosslinking density, dispersibility limit, and chemical doping efficiency by changing the knot to strut ratio. For the first time, we have shown that the processability issue of CPPs can be overcome by blending them with insulating commodity polymers. The blending of CPPs with poly(methylmethacrylate) (PMMA) has enabled them to be processed into thin films for conductivity measurements. The conductivity of strapped-CPPs is three orders of magnitude higher than that of the poly(phenyleneethynylene) porous network.

Post-synthetic π-extension of perylene conjugated porous polymer via APEX reactions: tunable optical and gas storage properties

Double post-synthetic modification is used for the π-extension of perylene based conjugated porous polymers (CPPs) using sequential annulative π-extension (APEX) reactions. This approach enabled us to synthesize new CPPs rendered with donor-acceptor rigid π-systems such as benzoperylene anhydride (BPA-CPP) and benzoperylene benzimidazole (BPBI-CPP) with distinct optical properties. Despite its low surface area, BPBI-CPP shows good CO₂ uptake and pH responsive behaviour owing to the presence of benzimidazole rings.

Fe-Immobilised Catechol-Based Hypercrosslinked Polymer as Heterogeneous Fenton Catalyst for Degradation of Methylene Blue in Water

Clean water is one of the sustainable development goals. Organic dye is one of the water pollutants affecting water quality. Hence, the conversion of dyes to safer species is crucial for water treatment. The Fenton reaction using Fe as a catalyst is a promising process. However, homogeneous catalysts are normally sensitive, difficult to separate, and burdensome to reuse. Therefore, a catechol-based hypercrosslinked polymer (catechol-HCP) was developed as an inexpensive solid support for Fe (catechol-HCP-Fe) and applied as a heterogenous Fenton catalyst. The good interaction of the catechol moiety with Fe, as well as the porous structure, simple preparation, low cost, and high stability of catechol-HCP, make it beneficial for Fe-loading in the polymer and Fenton reaction utilisation. The catechol-HCP-Fe demonstrated good catalytic activity for methylene blue (MB) degradation in a neutral pH. Complete decolouration of 100 ppm MB could be observed within 25 min. The rate of reaction was influenced by H₂O₂ concentration, polymer dose, MB concentration, pH, and temperature. The catechol-HCP-Fe could be reused for at least four cycles. The dominant reactive species of the reaction was considered to be singlet oxygen (¹O₂), and the plausible mechanism of the reaction was proposed.

Designed azo-linked conjugated microporous polymers for CO2 uptake and removal applications

In recent decade, conjugated microporous polymers (CMPs) were treated as one of the superior porous materials for CO₂ uptake. Herein, we prepared two azo-linked CMPs namely: azo-carbazole (Azo-Cz) and azo-phenothiazine (Azo-Tz) from the reduction of the corresponding nitro monomers using sodium borohydride (NaBH₄). The obtained polymers were well characterized using many spectroscopic techniques. According to TGA and BET analyses, our CMPs owned good specific surface areas (reaching 315 m² g^–1), and a significant thermal stability. It is also possessed pore sizes of 0.79 and 1.18 nm, respectively, and a reasonable char yields (max. 46 %). Based on CO₂ uptake measurements, the CO₂ adsorption capacities of these CMPs were very good: up to 40 and 94 mg g^–1 at the experiment temperatures 298 and 273 K, respectively. The great CO₂ uptake is due to high surface areas that facilitate powerful interactions with CO₂ molecules.

Two-dimensional conjugated microporous polymer films: fabrication strategies and potential applications

This review describes the latest advances in the preparation and application of two-dimensional conjugated microporous polymers, as well as the future research directions of this field.

Molecular Expansion for Constructing Porous Organic Polymers with High Surface Areas and Well-Defined Nanopores

Construction of porous organic polymers (POPs) with high surface areas, well-defined nanopores, and excellent stability remains extremely challenging because of the unmanageable reaction process. Until now, only a few reported POPs have Brunauer-Emmett-Teller (BET) surface areas (S_BET ) exceeding 3000 m²  g^-1 . Herein, we demonstrate a molecular expansion strategy to integrate high surface areas, large nanopore sizes, and outstanding stability into POPs. A series of hyper-crosslinked conjugated polymers (HCCPs) with exceptional porosity are synthesized through this strategy. Specially, HCCP-6 and HCCP-11 exhibit the highest surface areas (S_BET >3000 m²  g^-1 ) and excellent total pore volumes (up to 3.98 cm³  g^-1 ) among these HCCPs. They present decent total CH₄ storage capacities of 491 and 421 mg g^-1 at 80 bar and 298 K, respectively. Meanwhile, they are highly stable in harsh environments. The facile and general molecular expansion strategy would lead to improved synthetic routes of POPs for desired functions.

A Porous Aromatic Framework Functionalized with Luminescent Iridium(III) Organometallic Complexes for Turn-On Sensing of 99TcO4. ACS APPLIED MATERIALS & INTERFACES 2020;12:15288-15297. [PMID: 32131587 DOI: 10.1021/acsami.0c01929]

Contamination of ⁹⁹TcO₄^-, a problematic radioactive anion in the nuclear fuel cycle, in groundwater has been observed in a series of legacy nuclear sites, representing a notable radiation hazard and environmental concern. The development of convenient, rapid, and sensitive detection methods is therefore critical for radioactivity control and remediation tasks. Traditional detection methods suffer from clear demerits of either the presence of large interference from coexisting radioactive species (e.g., radioactivity counting methods) or the requirement of extensive instrumentation and analysis procedure (e.g., mass spectrometry). Here, we constructed a luminescent iridium(III) organometallic complex (Ir(ppy)₂(bpy)⁺; ppy = 2-phenylpyridine, bpy = 2,2^'-bipyridine)-grafted porous aromatic framework (Ir-PAF) for the first time, which can be utilized for efficient, facile, and selective detection of trace ReO₄^-/TcO₄^- in aqueous solutions. Importantly, the luminescence intensity of Ir-PAF is greatly enhanced in the presence of ReO₄^-/TcO₄^-, giving rise to a distinct turn-on sensor with the detection limit of 556.9 μg/L. Such a superior detection capability originates from the highly selective and strong interaction between ReO₄^-/TcO₄^- and Ir(ppy)₂(bpy)⁺, leading to an efficient pre-enrichment of ReO₄^-/TcO₄^- during analysis and subsequently a much weaker nonradiative decay of the luminescence of Ir(ppy)₂(bpy)⁺, as illustrated by density functional theory (DFT) calculation as well as quantum yield and fluorescence lifetime measurements. Successful quantification of trace ReO₄^- in simulated Hanford low-activity waste (LAW) solution containing large excess of Cl^-, NO₃^-, and NO₂^- was demonstrated, highlighting the bright future of luminescent PAFs in the area of chemical sensing.

Advances in Conjugated Microporous Polymers

Conjugated microporous polymers (CMPs) are a unique class of materials that combine extended π-conjugation with a permanently microporous skeleton. Since their discovery in 2007, CMPs have become established as an important subclass of porous materials. A wide range of synthetic building blocks and network-forming reactions offers an enormous variety of CMPs with different properties and structures. This has allowed CMPs to be developed for gas adsorption and separations, chemical adsorption and encapsulation, heterogeneous catalysis, photoredox catalysis, light emittance, sensing, energy storage, biological applications, and solar fuels production. Here we review the progress of CMP research since its beginnings and offer an outlook for where these materials might be headed in the future. We also compare the prospect for CMPs against the growing range of conjugated crystalline covalent organic frameworks (COFs).

One-Pot Fabrication of Pd Nanoparticles@Covalent-Organic-Framework-Derived Hollow Polyamine Spheres as a Synergistic Catalyst for Tandem Catalysis

Facile fabrication of nanocatalysts consisting of metal nanoparticles (NPs) anchored on a functional support is highly desirable, yet remains challenging. Covalent organic frameworks (COFs) provide an emerging materials platform for structural control and functional design. Here, a facile one-pot in situ reduction approach is demonstrated for the encapsulation of small Pd NPs into the shell of COF-derived hollow polyamine spheres (Pd@H-PPA). In the one-pot synthetic process, the nucleation and growth of Pd NPs in the cavities of the porous shell take place simultaneously with the reduction of imine linkages to secondary amine groups. Pd@H-PPA shows a significantly enhanced catalytic activity and recyclability in the tandem dehydrogenation of ammonia borane and selective hydrogenation of nitroarenes through an adsorption-activation-reaction mechanism. The strong interactions of the secondary amine linkage with borane and nitroarene molecules afford a positive synergy to promote the catalytic reaction. Moreover, the hierarchical structure of Pd@H-PPA allows the accessibility of active Pd NPs to reactants.

Conjugated porous polymers: incredibly versatile materials with far-reaching applications

This review discusses conjugated porous polymers and focuses on relating design principles and synthetic methods to key properties and applications such as (photo)catalysis, gas storage, chemical sensing, energy storage and environmental remediation.

Synthesis of 1,6-disubstituted pyrene-based conjugated microporous polymers for reversible adsorption and fluorescence sensing of iodine

Four 1,6-disubstituted pyrene-based fluorescent conjugated microporous polymers were synthesized by Sonogashira–Hagihara reaction, trimerization reaction of –CN, and Friedel–Crafts reaction, respectively, which can efficient capture and sense I₂.

Porous networks based on iron(ii) clathrochelate complexes

Microporous networks based on boronate ester-capped iron(ii) clathrochelate complexes are described. The networks were obtained by covalent cross-linking of tetrabrominated clathrochelate complexes via Suzuki-Miyaura polycross-coupling reactions with diboronic acids, or by Sonogashira-Hagihara polycross-coupling of clathrochelate complexes with terminal alkyne functions and 1,3,5-tribromobenzene. The networks display permanent porosity with apparent Brunauer-Emmett-Teller surface areas of up to SABET = 593 m2 g-1. A clathrochelate complex based on an enantiopure dioximato ligand was used to prepare chiral networks. One of these networks was shown to preferentially absorb d-tryptophan over l-tryptophan.

Facile synthesis of conjugated microporous polymer-based porphyrin units for adsorption of CO2 and organic vapors

Two porphyrin-based CMPs as multifunctional absorbents exhibit high CO₂ selectivity over N₂ and CH₄ and good capacity for organic vapors.

Dispersible microporous diblock copolymer nanoparticles via polymerisation-induced self-assembly

Dispersible microporous polymer nanoparticles formed via the RAFT-PISA polymerisation of divinylbenzene and fumaronitrile using a PEG macro-CTA.

Ag+ doped into azo-linked conjugated microporous polymer for volatile iodine capture and detection of heavy metal ions

We herein report the construction of a novel azo-linked conjugated microporous polymers (Ag@Azo_TPE-CMP), which possesses permanent porous structure and Ag⁺ loading up of 7.62% in the skeleton as effective sorption sites. Ag@Azo_TPE-CMP shows considerable adsorption capacity of iodine of 202 wt% in iodine vapor at 350 K. In addition, Ag@Azo_TPE-CMP can effectively remove heavy ions from ethanol-water solution.

Supramolecular Reassembly of Self-Exfoliated Ionic Covalent Organic Nanosheets for Label-Free Detection of Double-Stranded DNA

Ionic covalent organic nanosheets (iCONs), a member of the two-dimensional (2D) nanomaterials family, offer a unique functional platform for a wide range of applications. Herein, we explore the potential of an ethidium bromide (EB)-based covalent organic framework (EB-TFP) that self-exfoliates in water resulting in 2D ionic covalent organic nanosheets (EB-TFP-iCONs) for the selective detection of double-stranded DNA (dsDNA). In an aqueous medium, the self-exfoliated EB-TFP-iCONs reassemble in the presence of dsDNA resulting in hybrid EB-TFP-iCONs-DNA crystalline nanosheets with enhanced fluorescence at 600 nm. Detailed steady-state and time-resolved emission studies revealed that the reassembly phenomenon was highly selective for dsDNA when compared to single-stranded DNA (ssDNA), which allowed us to use the EB-TFP-iCONs as a 2D fluorescent platform for the label-free detection of complementary DNA strands.

Conjugated microporous polymers with azide groups: a new strategy for postsynthetic fluoride functionalization and effectively enhanced CO2 adsorption properties

A series of conjugated microporous polymers (CMPs) have been synthesized based on zinc-porphyrin building blocks. Azide groups incorporated within the pores of the CMPs were subjected to alkyne click conditions via a facile, one-step quantitative procedure, the resultant porous frameworks exhibited enhanced CO₂ sorption properties.

Metal-Free Motifs for Solar Fuel Applications

Metal-free motifs, such as graphitic carbon nitride, conjugated polymers, and doped nanostructures, are emerging as a new class of Earth-abundant materials for solar fuel devices. Although these metal-free structures show great potential, detailed mechanistic understanding of their performance remains limited. Here, we review important experimental and theoretical findings relevant to the role of metal-free motifs as either photoelectrodes or electrocatalysts. First, the light-harvesting characteristics of metal-free photoelectrodes (band energetics, exciton binding energies, charge carrier mobilities and lifetimes) are discussed and contrasted with those in traditional inorganic semiconductors (such as Si). Second, the mechanistic insights into the electrocatalytic oxygen reduction and evolution reactions, hydrogen evolution reaction, and carbon dioxide reduction reaction by metal-free motifs are summarized, including experimental surface-sensitive spectroscopy findings, studies on small molecular models, and computational modeling of these chemical transformations.

Design of multi-functional 2D open-shell organic networks with mechanically controllable properties

Triarylmethyls (TAMs) are prominent highly attractive open shell organic molecular building blocks for materials science, having been used in breakthrough syntheses of organic magnetic polymers and metal organic frameworks. With their radical π-conjugated nature and a proven capacity to possess high stability via suitable chemical design, TAMs display a variety of desirable characteristics which can be exploited for a wide range of applications. Due to their particular molecular and electronic structure, the spin localization in TAMs almost entirely depends on the dihedral angles of their three aryl rings with respect to the central methyl carbon atom plane, which opens up the possibility of controlling their fundamental properties by twisting the three aryl rings. Aryl ring twist angles can be tuned to a single value by specific chemical functionalisation but controlling them by external means in organic materials or devices represents a challenging task which has not yet been experimentally achieved. Herein, through rational chemical design we propose two 2D covalent organic frameworks (2D-COFs) based on specific TAM building blocks. By employing ab initio computational modeling we demonstrate that it is possible to externally manipulate the aryl ring twist angles in these 2D-linked TAM frameworks by external mechanical means. Furthermore, we show this structural manipulation allows for finely tuning the most important characteristics of these materials such as spin localization, optical electronic transitions and magnetic interactions. Due to the enormous technological potential offered by this new class of material and the fact that our work is guided by real advances in organic materials synthesis, we believe that our predictions will inspire the experimental realization of radical-2D-COFs with externally controllable characteristics.

Microporous polyimide networks constructed through a two-step polymerization approach, and their carbon dioxide adsorption performance

A series of microporous polyimide networks were preparedviaa novel two-step pathway combining polymerization and crosslinking reactions.

Responsive Guest Encapsulation of Dynamic Conjugated Microporous Polymers

The host-guest complexes of conjugated microporous polymers encapsulating C₆₀ and dye molecules have been investigated systematically. The orientation of guest molecules inside the cavities, have different terms: inside the open cavities of the polymer, or inside the cavities formed by packing different polymers. The host backbone shows responsive dynamic behavior in order to accommodate the size and shape of incoming guest molecule or guest aggregates. Simulations show that the host-guest binding of conjugated polymers is stronger than that of non-conjugated polymers. This detailed study could provide a clear picture for the host-guest interaction for dynamic conjugated microporous polymers. The mechanism obtained could guide designing new conjugated microporous polymers.

Solid-state emissive cyanostilbene based conjugated microporous polymers via cost-effective Knoevenagel polycondensation

Solid-state emissive cyanostilbene-based conjugated porous polymers with different topological structure and photophysical properties were newly synthesized via cost-effective Knoevenagel polycondensation.

Porphyrin and pyrene-based conjugated microporous polymer for efficient sequestration of CO2 and iodine and photosensitization for singlet oxygen generation

A novel porphyrin and pyrene-based conjugated microporous polymer (Por-Py-CMP) was synthesized. It exhibited a high BET surface area (1014 m² g⁻¹) and excellent capacity for capturing CO₂ and I₂. It also showed high efficiency for ¹O₂ generation.

Tetraphenylethylene-based microporous organic polymers: insight into structure geometry, porosity, and CO2/CH4 selectivity

Tetraphenylethylene-based microporous organic polymers with tunable porosities were synthesized and their gas sorption capabilities were investigated.

Dynamic, conjugated microporous polymers: visible light harvesting via guest-responsive reversible swelling

Dynamic conjugated microporous polymers of pyrene entrap guest molecules rapidly at room temperature via swelling and show efficient host–guest energy-transfer.

Compressible and monolithic microporous polymer sponges prepared via one-pot synthesis

Compressible and monolithic microporous polymers (MPs) are reported. MPs were prepared as monoliths via a Sonogashira–Hagihara coupling reaction of 1,3,5-triethynylbenzene (TEB) with the bis(bromothiophene) monomer (PBT-Br). The polymers were reversibly compressible, and were easily cut into any form using a knife. Microscopy studies on the MPs revealed that the polymers had tubular microstructures, resembling those often found in marine sponges. Under compression, elastic buckling of the tube bundles was observed using an optical microscope. MP-0.8, which was synthesized using a 0.8:1 molar ratio of PBT-Br to TEB, showed microporosity with a BET surface area as high as 463 m²g^–1. The polymer was very hydrophobic, with a water contact angle of 145° and absorbed 7–17 times its own weight of organic liquids. The absorbates were released by simple compression, allowing recyclable use of the polymer. MPs are potential precursors of structured carbon materials; for example, a partially graphitic material was obtained by pyrolysis of MP-0.8, which showed a similar tubular structure to that of MP-0.8.

Fabrication of porous organic polymers in the form of powder, soluble in organic solvents and nanoparticles: a unique platform for gas adsorption and efficient chemosensing

Tetraphenyl-5,5-dioctylcyclopentadiene based porous organic polymers were fabricated in the form of powder, soluble in organic solvents and nanoparticles and were explored for gas adsorption and chemosensing.

Octavinylsilsesquioxane-based luminescent nanoporous inorganic–organic hybrid polymers constructed by the Heck coupling reaction

A class of luminescent nanoporous inorganic–organic hybrid polymers has been synthesized by the Heck coupling of octavinylsilsesquioxane with aromatic bromide monomers. The resulting materials exhibit porous and luminescent features, and show picric acid sensing behaviour.

Amide functionalized microporous organic polymer (Am-MOP) for selective CO₂ sorption and catalysis

We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (-CONH-) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N2, Ar, and O2. The CO2 molecule interacts with amide functional groups via Lewis acid-base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.