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.

A Sensitive Photoelectrochemical Sensor for Levodopa Detection Using Benzothiadiazole-Based Conjugated Microporous Polymer-Coated Graphene Heterostructures

Since the 1960s, levodopa (LDA) has been the standard drug for treating of Parkinson's disease. In this study, a novel benzothiadiazole-based conjugated microporous polymer-coated graphene heterostructure (CMP-rGO) was synthesized and used to construct a sensitive photoelectrochemical (PEC) sensor capable of detecting LDA. Under optimal experimental conditions, the intensity of the photocurrent produced by the sensor was linear from 0.005 to 40 μM, and the limit of detection of the sensor was 0.0027 μM. The sensor showed good repeatability, stability, and selectivity for LDA detection. Finally, the constructed sensor was used to detect LDA in levodopa tablets, human serum samples, and urine samples and satisfactory results were obtained. Therefore, the PEC sensor provides a novel platform for the detection of LDA in real samples and broadens the applications of conjugated microporous polymers in PEC sensing.

Porous Organic Polymers: Promising Testbed for Heterogeneous Reactive Oxygen Species Mediated Photocatalysis and Nonredox CO2 Fixation

Catalysts play a pivotal role in achieving the global need for food and energy. In this context, porous organic polymers (POPs) with high surface area, robust architecture, tunable pore size, and chemical functionalities have emerged as promising testbeds for heterogeneous catalysis. Amorphous POPs having functionalized interconnected hierarchical porous structures activate a diverse range of substrates through covalent/non-covalent interactions or act as a host matrix to encapsulate catalytically active metal centers. On the other hand, conjugated POPs have been explored for photoinduced chemical transformations. In this personal account, we have delineated the evolution of various POPs and the specific role of pores and pore functionalities in heterogeneous catalysis. Subsequently, we retrospect our journey over the last ten years towards designing and fabricating amorphous POPs for heterogeneous catalysis, specifically photocatalytic reactive oxygen species (ROS)-mediated organic transformations and nonredox chemical fixation of CO₂ . We have also outlined some of the future avenues of POPs and POP-based hybrid materials for diverse catalytic applications.

Red edge effect and chromoselective photocatalysis with amorphous covalent triazine-based frameworks

Chromoselective photocatalysis offers an intriguing opportunity to enable a specific reaction pathway out of a potentially possible multiplicity for a given substrate by using a sensitizer that converts the energy of incident photon into the redox potential of the corresponding magnitude. Several sensitizers possessing different discrete redox potentials (high/low) upon excitation with photons of specific wavelength (short/long) have been reported. Herein, we report design of molecular structures of two-dimensional amorphous covalent triazine-based frameworks (CTFs) possessing intraband states close to the valence band with strong red edge effect (REE). REE enables generation of a continuum of excited sites characterized by their own redox potentials, with the magnitude proportional to the wavelength of incident photons. Separation of charge carriers in such materials depends strongly on the wavelength of incident light and is the primary parameter that defines efficacy of the materials in photocatalytic bromination of electron rich aromatic compounds. In dual Ni-photocatalysis, excitation of electrons from the intraband states to the conduction band of the CTF with 625 nm photons enables selective formation of C‒N cross-coupling products from arylhalides and pyrrolidine, while an undesirable dehalogenation process is completely suppressed.

Charge Transfer from Donor to Acceptor in Conjugated Microporous Polymer for Enhanced Photosensitization

Photosensitization associated with light absorption and energy/electron-transfer represents the central processes for photosynthesis. However, it's still a challenge to develop a heavy-atom-free (HAF) strategy to improve the sensitizing ability of polymeric photosensitizers. Herein, we propose a new protocol to significantly improve the photosensitization by decorating mother conjugated microporous polymer (CMP-1) with polycyclic aromatic hydrocarbons (PAHs), resulting in a series of CMPs (CMP-2-4). Systematic study reveals that covalent modification with PAHs can transfer charge to Bodipy in CMP to further facilitate both intersystem crossing and electron-hole separation, which can dramatically boost energy-/electron-transfer reactions. Remarkably, CMP-2 as a representative CMP can efficiently drive the photosynthesis of methyl phenyl sulfoxide with 92 % yield, substantially higher than that of CMP-1 (32 %). Experiments and theory calculations demonstrate the structure-property-activity relationship of these CMPs, opening a new horizon for developing HAF heterogeneous photosensitizers with highly efficient sensitizing activity by rational structure regulation at a molecular level.

Room-Temperature Synthesis of a Hollow Microporous Organic Polymer Bearing Activated Alkyne IR Probes for Nonradical Thiol-yne Click-Based Post-Functionalization

This work shows that hollow microporous organic polymer (H-MOP-A) with activated internal alkynes as IR probes can be prepared by template synthesis based on acyl Sonogashira-Hagihara coupling at room temperature. The H-MOP-A is a versatile platform in the main chain PSM based on nonradical thiol-yne click reaction. Moreover, an IR peak of internal alkynes in the H-MOP-A is very intense and could be utilized in the monitoring of thiol-yne click-based main chain PSM. The functionalized H-MOP-A with carboxylic acids (H-MOP-CA) showed efficient adsorption toward Ag⁺ ions. The resultant H-MOP-CA-Ag showed excellent performance in the CO₂ fixation to α-alkylidene cyclic compounds.

Beyond C3N4 π-conjugated metal-free polymeric semiconductors for photocatalytic chemical transformations

Photocatalysis with stable, efficient and inexpensive metal-free catalysts is one of the most promising options for non-polluting energy production. This review article covers the state-of-the-art development of various effective metal-free polymeric photocatalysts with large π-conjugated units for chemical transformations including water splitting, CO2 and N2 reduction, organic synthesis and monomer polymerisation. The article starts with the catalytic mechanisms of metal-free photocatalysts. Then a particular focus is on the rational manipulation of π-conjugation enlargement, charge separation, electronic structures and band structures in the design of metal-free polymeric photocatalysts. Following the design principles, the selection and construction of functional units are discussed, as well as the connecting bonds and dimensions of π-conjugated polymeric photocatalysts. Finally the hot and emerging applications of metal-free polymeric photocatalysts for photocatalytic chemical transformations are summarized. The strategies provide potential avenues to address the challenges of catalyst activity, selectivity and stability in the further development of highly effective metal-free polymeric photocatalysts.

Structure–activity relationships in well-defined conjugated oligomer photocatalysts for hydrogen production from water

Oligomer chain length and backbone twisting were found to have a strong effect on optoelectronic properties but a trimer of dibenzo[b,d]thiophene sulfone was found to have high photocatalytic activity approaching that of its polymer analogue.

Porous Cationic Covalent Triazine-Based Frameworks as Platforms for Efficient CO2 and Iodine Capture

Porous cationic covalent triazine-based frameworks (CTFs) with imidazolium salts as tectons were prepared via ionothermal synthesis. The high-PF₆ ^- -content CTF shows the CO₂ adsorption of 44.7 cm³  g^-1 and I₂ capture capacity of 312 wt %. The influence of counterion species and contents on the porosities, CO₂ adsorptions, and I₂ capture capacities of the CTFs has been investigated.

Fluorescent Sulphur- and Nitrogen-Containing Porous Polymers with Tuneable Donor-Acceptor Domains for Light-Driven Hydrogen Evolution

Light-driven water splitting is a potential source of abundant, clean energy, yet efficient charge-separation and size and position of the bandgap in heterogeneous photocatalysts are challenging to predict and design. Synthetic attempts to tune the bandgap of polymer photocatalysts classically rely on variations of the sizes of their π-conjugated domains. However, only donor-acceptor dyads hold the key to prevent undesired electron-hole recombination within the catalyst via efficient charge separation. Building on our previous success in incorporating electron-donating, sulphur-containing linkers and electron-withdrawing, triazine (C₃ N₃ ) units into porous polymers, we report the synthesis of six visible-light-active, triazine-based polymers with a high heteroatom-content of S and N that photocatalytically generate H₂ from water: up to 915 μmol h^-1  g^-1 with Pt co-catalyst, and-as one of the highest to-date reported values -200 μmol h^-1  g^-1 without. The highly modular Sonogashira-Hagihara cross-coupling reaction we employ, enables a systematic study of mixed (S, N, C) and (N, C)-only polymer systems. Our results highlight that photocatalytic water-splitting does not only require an ideal optical bandgap of ≈2.2 eV, but that the choice of donor-acceptor motifs profoundly impacts charge-transfer and catalytic activity.

Highly efficient removal of organic pollutants by ultrahigh-surface-area-ethynylbenzene-based conjugated microporous polymers via adsorption–photocatalysis synergy

Conjugated microporous polymers with a high surface area and a narrow band gap exhibited efficient removal of organic pollutants via adsorption–photocatalysis synergy.

A facile route to prepare dimeric BODIPY-based porous organic polymers using FeCl3

A facile FeCl₃ catalyzed oxidation of the dimeric BODIPY monomers with different spacers to construct porous organic polymers have been reported. These polymers’ singlet oxygen generation capacities are dependent on the spacers.

Fluorescence-Tuned Polyhedral Oligomeric Silsesquioxane-Based Porous Polymers

Two series of new polyhedral oligomeric silsesquioxane (POSS)-based fluorescent hybrid porous polymers, HPP-1 and HPP-2, have been prepared by the Heck reaction of octavinylsilsesquioxane with 2,2',7,7'-tetrabromo-9,9'-spirobifluorene and 1,3,6,8-tetrabromopyrene, respectively. Three sets of reaction conditions were employed to assess their effect on fluorescence. These materials exhibit tunable fluorescence from nearly no fluorescence to bright fluorescence both in the solid state and dispersed in ethanol under UV light irradiation by simply altering the reaction conditions. We speculated that the difference may be attributable to the fluorescence quenching induced by Et3 N, P(o-CH3 Ph)3 , and their hydrogen bromide salts employed in the reactions. This finding could give valuable suggestions for the construction of porous polymers with tunable/controllable fluorescence, especially those prepared by Heck and Sonogashira reactions in which these quenchers are used as organic bases or co-catalysts. In addition, the porosities can also be tuned, but different trends in porosity have been found in these two series of polymers, which suggests that various factors should be carefully considered in the preparation of porous polymers with tunable/controllable porosity. Furthermore, HPP-1 c showed moderate CO2 uptake and fluorescence that was efficiently quenched by nitroaromatic explosives, thereby indicating that these materials could be utilized as solid absorbents for the capture and storage of CO2 and as sensing agents for the detection of explosives.

One-step fabrication of porous oxygen-doped g-C3N4 with feeble nitrogen vacancies for enhanced photocatalytic performance

Porous oxygen-doped g-C₃N₄ with feeble nitrogen vacancies was fabricated via a one-step method to enhance its photocatalytic performance.

Conjugated Microporous Poly(Benzochalcogenadiazole)s for Photocatalytic Oxidative Coupling of Amines under Visible Light

Metal-free visible-light photocatalysts offer a clean, sustainable solution to many pressing environmental issues. Herein, we present a molecular design strategy to fine-tune the valence and conduction band levels of a series of conjugated microporous polymer networks based on poly(benzochalcogenadiazole) for heterogeneous photocatalysis. Enhanced photocatalytic efficiency was observed by altering the chalcogene moieties in the electron-accepting benzochalcogenadiazole unit of the polymer backbone structure. Photooxidative coupling of benzylamines was chosen as a model reaction. This design strategy leading to enhanced efficiency could potentially improve a wide range of photoredox reactions.