Thiazolo[5,4‑d]thiazole linked conjugated microporous polymer photocatalysis for selective aerobic oxidation of amines

D1-D2-A ternary conjugated microporous polymers synthesized via direct CH arylation for enhancing photocatalytic hydrogen evolution

Conjugated microporous polymers (CMPs), featured by broad tunability in molecule design, structure and properties, have been widely used as photocatalysts for water splitting to produce hydrogen. However, the conventional donor-acceptor (D-A) binary CMPs have not achieved satisfactory performance so far. In this contribution, a series of D1-D2-A ternary CMPs are synthesized by the atom-economical direct CH arylation polymerization (DArP), wherein the dibenzo[b,d]thiophene-S,S-dioxide (BTDO), tetraphenylethylene (TPE) and 3,4-ethylenedioxythiophene (EDOT) units serve as the acceptor (A), donor D1 and donor D2, respectively. The structure-property correlations of the CMPs are systematically investigated by optical, electrochemical, water contact angle, and hydrogen production performance tests, revealing that the ternary D1-D2-A CMPs can maximize hydrophilicity and charge separation through the synergistic effect of BTDO, EDOT, and TPE building blocks. As a result, the ternary CMP-3 with an optimal D/A ratio achieves the highest photocatalytic hydrogen evolution rate up to 81.4 mmol g-1 h-1 without the aid of Pt co-catalyst, which has a 26-fold and 101-fold improvement compared to the pristine D1-A and D1-D2 binary CMPs, respectively. Meanwhile, a high apparent quantum yield of 11.1 % at 500 nm is successfully achieved. Density functional theory calculation discloses that D1-D2-A ternary CMPs possess the desirable molecular geometry and superior charge separation. This work provides a new design and synthetic strategy for the high-performance CMP-based photocatalysts.

Photocatalytic detoxification of a sulfur mustard simulant using donor-enhanced porphyrin-based covalent-organic frameworks

Photocatalytic detoxification of sulfur mustards (e.g., bis (2-chloroethyl) sulfide, SM) is an effective approach for protecting the ecological environment and human health. In order to fabricate COFs with high performance for the selective transformation of the SM simulant 2-chloroethyl ethyl sulfide (CEES) to nontoxic 2-chloroethyl ethyl sulfoxide (CEESO), three porphyrin-based COFs with different donor groups (R = H, OH, and OMe) were synthesized. Among these COFs, COF-OMe, which possesses the strongest electron-donating ability, demonstrated a faster and higher detoxification rate of CEES at various concentrations, achieving selective oxidation of CEES to non-toxic CEESO with 99.2% conversion and 100% selectivity using white LED light irradiation within three hours. The facilitated charge transfer and separation as well as efficaciously produced reactive oxygen species (ROS), including singlet oxygen (1O2) and superoxide radical anions (O2˙-) are supposed to contribute to the excellent performance. The results demonstrated that the donor-enhanced porphyrin-based COFs could act as heterogeneous photocatalysts for visible light driven organic transformation and detoxification of sulfur mustards.

Toward Pore Size-Selective Photoredox Catalysis Using Bifunctional Microporous 2D Triazine-Based Covalent Organic Frameworks

The design and synthesis of photoactive metal-free 2D materials for selective heterogeneous photoredox catalysis continue to be challenging due to issues related to nonrecyclability, and limited photo- and chemical stability. Herein, we report the photocatalytic properties of a triazine-based porous COF, TRIPTA, which is found to be capable of facilitating both SET (single electron transfer) for photocatalytic reductive debromination of phenacyl bromide in absence of oxygen and generation of reactive oxygen species (ROS) for benzylamine photo-oxidation in the presence of oxygen, respectively, under visible light irradiation. Inspired by the latter results, we further systematically investigated different-sized benzylamine substrates in this single-component reaction and compared the results with an analogous COF (Micro-COF-2) exhibiting a larger pore size. We observed a marked improvement in the conversion of larger-sized substrates with the latter COF, thereby demonstrating angstrom-level pore size-selective photocatalytic activity of COFs.

Salt-templated porous melamine-based conjugated polymers for selective oxidation of amines into imines under visible light

Conjugated polymers have a broad application foreground in the field of photocatalytic organic synthesis to produce value-added chemicals due to their functional diversity, broad light responsive ability, high thermal and chemical stability, and tunable band structure. Herein, using mixed chloride salts (i.e., NaCl/LiCl) as building template, a series of porous conjugated polymers constructed by melamine and terephthalaldehyde monomers were obtained through a Schiff-base reaction in the absence of any external solvent. Melamine-terephthalaldehyde polymer (i.e., PMTPA-x, x represents the mass ratio of salt-mixture to mixed precursors of PMTPA) materials displayed porous morphologies and possessed different energy band structures via regulating the mass ratio of mixed-salt to monomers. Specifically, PMTPA-20 has a larger specific surface area and more suitable redox potential towards the photocatalytic oxidative coupling of amines to imines. Under visible light, with molecular oxygen as oxidant, PMTPA-20 achieves 97% conversion of benzylamine in 8 h which is 3.9 times higher than that of pristine PMTPA (25% conversion in 8 h). In addition, PMTPA-20 catalyst has good structure stability and reusability performance for photocatalytic reactions.

Triazine-based two dimensional porous materials for visible light-mediated oxidation of sulfides to sulfoxides with O2

Recently, triazine-based two dimensional (2D) porous materials have received increasing attention in photocatalysis. Herein, CTF-1, a covalent triazine framework, was adopted as the blueprint for designing a 2D bespoke photocatalyst. The thiazolo[5,4-d]thiazole (TzTz) linkage was inserted into the framework of CTF-1, affording TzTz-TA, which belongs to conjugated microporous polymers (CMPs). Rather than the direct insertion via the challenging CH activation, TzTz-TA was assembled from 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and dithiooxamide, in which TzTz was formed in situ by a process of catalyst-free solvothermal condensation. Both CTF-1 and TzTz-TA had similar energy gaps (E_g), photocurrents, and charge carrier lifetimes, in line with the similar molecular underpinnings. However, the reduction potential of TzTz-TA is less negative than that of CTF-1 due to the insertion of TzTz linkage, in a more appropriate position for activating O₂ to superoxide (O₂^•-). In return, blue light-mediated oxidation of sulfides to sulfoxides with O₂ over TzTz-TA was accomplished with significantly superior conversions to those over CTF-1. Intriguingly, extensive sulfides could be oxidized to corresponding sulfoxides with outstanding recycling stability of TzTz-TA. Notably, attendance of an induction period was observed during TzTz-TA photocatalysis. This work highlights the vast potential of designing triazine-based porous materials to meet the tailor-made demands, such as the oxidative transformation of organic molecules with O₂.

Visible Light-Induced Aerobic Oxidative Dehydrogenation of C-N/C-O to C=N/C=O Bonds Using Metal-Free Photocatalysts: Recent Developments

Performing synthetic transformation using visible light as energy source, in the presence of a photocatalyst as a promoter, is currently of high interest, and oxidation reactions carried out under these conditions using oxygen as the final oxidant are particularly convenient from an environmental point of view. This review summarizes the recent developments achieved in the oxidative dehydrogenation of C-N and C-O bonds, leading to C=N and C=O bonds, respectively, using air or pure oxygen as oxidant and metal-free homogeneous or recyclable heterogeneous photocatalysts under visible light irradiation.

Digital-intellectual design of microporous organic polymers

Microporous organic polymers (MOPs) are a new class of microporous materials. Due to their high porosity, large pore volume, and large surface area, MOPs exhibit excellent performance in gas adsorption and storage, membrane separation, ion capture, heterogeneous catalysis, light energy conversion and storage, capacitance, and other fields. However, selecting high-performance materials for specific applications from thousands of candidate MOPs is a key problem. Traditional design strategies for new materials with targeted properties, including trial-and-error and relying on the experiences of domain experts, are time- and cost-consuming. With the rapid development of computation technology and theoretical chemistry, the discovery of new materials is no longer a purely experimental subject. Breaking away from the traditional trial-and-error strategy for materials discovery, materials design is emerging and gaining increasing attention. In addition, the ability to collect "big data" has greatly improved and has further stimulated the development of new methods for materials design and discovery. In this perspective, we examine how data-driven techniques combine artificial intelligence (AI) and human expertise, playing a significant role in the design of MOPs. Such analytics can significantly reduce time-to-insight and accelerate the cost-effective materials discovery, which is the goal for designing future MOPs.

The crystal structure of 2,5-bis(3,5-dimethylphenyl)thiazolo[5,4-d]thiazole, C20H18N2S2

C20H18N2S2, monoclinic, P21/n (no. 14), a = 7.92140(10) Å, b = 6.08080(10) Å, c = 17.8091(3) Å, β = 90.592(2)°, V = 857.79(2) Å3, Z = 4, R gt(F) = 0.0382, wR ref(F 2) = 0.1051, T = 149.99(10) K.

CCDC no.: 2085420

A boranil-based conjugated microporous polymer for efficient visible-light-driven heterogeneous photocatalysis

A new boranil-dye-incorporated conjugated microporous polymer was designed and employed as an effective heterogeneous photocatalyst for aerobic oxidation of sulfides and primary amines.