Structural Engineering of Donor−π–Acceptor Conjugated Polymers for Facilitating Charge Separation: A Dual-Functional Photocatalysis

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.

Develop Complex Photocatalytic System of D-π-A-type Conjugated Porous Polymers and Benzyl Alcohol Mediated Autocatalysis for Practical Artificial Photosynthesis of H2O2

Artificial photosynthesis of H2O2 is conceived to be an ideal approach for replacing the industrial anthraquinone method that suffers from hefty energy penalties and environmental toxicity. However, the low concentration of H2O2 resides as the biggest hurdle for industrial production. Herein, with a focus on fabricating high-performance heterogeneous photocatalysts and establishing a highly efficient complex photocatalytic system, we report the preparation of D-π-A-type conjugated porous polymers containing a photosensitizer and redox-active anthraquinone moiety for endowing highly efficient H2O2 production up to 3.0 mmol g-1 h-1. Further, by exploiting the autocatalytic photooxidation feature of benzyl alcohol, •OOH as the key species contributing to H2O2 formation received a substantial accumulation, which stems from the collaboration of the photocatalytic and autocatalytic cycle. Mechanistically, the hydrogen bonding and π-π stacking between the photocatalyst and benzyl alcohol are formed to lower the free energy of the transition states, thus leading to unprecedentedly high efficiency in the photosynthesis of H2O2 up to 140.4 mmol g-1 h-1, with the concentration of 35.1 mmol L-1 and an apparent quantum yield of 49%. This work provides critical insights in advancing sustainable energy conversion research.

Modulating π-bridge in donor-π-acceptor covalent organic frameworks for low-energy-light-driven photocatalytic reaction

Most of the photocatalytic reactions are currently driven by high-energy light (UV, blue light), which inevitably leads to side reactions and co-catalyst deactivation. Therefore, there is an urgent need to prepare novel photocatalysts with low-energy photocatalytic properties. Herein, we report a rational molecular design of covalent organic frameworks (COFs) equipped with donor-π-acceptor systems with different π-bridges (aromatic ring, mono- and bis-alkynyl). It was found that the COF with mono-alkynes as a π-bridge (TP-EDAE) can accelerate the rapid carrier migration even under low-energy light compared to the other two types of π-bridges (aromatic ring and bis-alkynyl), which was conducive to the photocatalytic redox reactions. As a result, the TP-EDAE samples showed high CO coupling activity and good substrate versatility under both high-energy light (blue light) and low-energy light (green light), especially the TP-EDAE samples displayed high stability with no obvious activity decay within five cycles under low-energy light. This work highlights the fundamental molecular design of advanced functionalized COFs with specific π-bridges for photocatalytic organic reactions under low-energy light.

A Versatile Strategy toward Donor-Acceptor Nanofibers with Tunable Length/Composition and Enhanced Photocatalytic Activity

Living crystallization-driven self-assembly (CDSA) has emerged as an efficient strategy to generate nanofibers of π-conjugated polymers (CPNFs) in a controlled fashion. However, reports of donor-acceptor (D-A) heterojunction CPNFs are extremely rare. The preparation of these materials remains a challenge due to the lack of rational design guidelines for the D-A π-conjugated units. Herein, we report a versatile CDSA strategy based upon carefully designed D-A-co-oligomers in which electron-deficient benzothiadiazole (BT) or dibenzo[b,d]thiophene 5,5-dioxide (FSO) units are attached to the two ends of an oligo(p-phenylene ethynylene) heptamer [BT-OPE7-BT, FSO-OPE7-FSO]. This arrangement with the electron-deficient groups at the two ends of the oligomer enhances the stacking interaction of the A-D-A π-conjugated structure. In contrast, D-A-D structures with a single BT in the middle of a string of OPE units disrupt the packing. We employed oligomers with a terminal alkyne to synthesize diblock copolymers BT-OPE7-BT-b-P2VP and BT-OPE7-BT-b-PNIPAM (P2VP = poly(2-vinylpyridine), PNIPAM = poly(N-isopropylacrylamide)) and FSO-OPE7-FSO-b-P2VP and FSO-OPE7-FSO-b-PNIPAM. CDSA experiments with these copolymers in ethanol were able to generate CPNFs of controlled length by both self-seeding and seeded growth as well as block comicelles with precisely tunable length and composition. Furthermore, the D-A CPNFs with a BT-OPE7-BT-based core demonstrate photocatalytic activity for the photooxidation of sulfide to sulfoxide and benzylamine to N-benzylidenebenzylamine. Given the scope of the oligomer compositions examined and the range of structures formed, we believe that the living CDSA strategy with D-A-based co-oligomers opens future opportunities for the creation of D-A CPNFs with programmable architectures as well as diverse functionalities and applications.

Radical Stitching Polymerization and Its Alternating Copolymerization

Polymers possessing saturated fused polycycles in the main chain repeating unit have been underexplored despite their potential utility based on their expected properties such as high rigidity, chemical resistance, transparency, and thermal stability. In this regard, herein, we developed a radical stitching polymerization of styryl vinyl ketones for the synthesis of polyketones possessing saturated fused bicyclic repeating units. The polymerization proceeded smoothly with a high degree of stitching efficiency in a chain-growth manner under free radical conditions. This method was further extended to the alternating copolymerization of styryl vinyl ketones and 1-styryl-2-vinylbenzenes, representing the first alternating stitching copolymerization of two different monomers. The obtained polymers were found to show promising thermal properties and high transparency in the visible light region.

Efficient integration of covalent triazine frameworks (CTFs) for augmented photocatalytic efficacy: A review of synthesis, strategies, and applications

Heterogeneous photocatalysis emerges as an exceptionally appealing technological avenue for the direct capture, conversion, and storage of renewable solar energy, facilitating the generation of sustainable and ecologically benign solar fuels and a spectrum of other pertinent applications. Heterogeneous nanocomposites, incorporating Covalent Triazine Frameworks (CTFs), exhibit a wide-ranging spectrum of light absorption, well-suited electronic band structures, rapid charge carrier mobility, ample resource availability, commendable chemical robustness, and straightforward synthetic routes. These attributes collectively position them as highly promising photocatalysts with applicability in diverse fields, including but not limited to the production of photocatalytic solar fuels and the decomposition of environmental contaminants. As the field of photocatalysis through the hybridization of CTFs undergoes rapid expansion, there is a pressing and substantive need for a systematic retrospective analysis and forward-looking evaluation to elucidate pathways for enhancing performance. This comprehensive review commences by directing attention to diverse synthetic methodologies for the creation of composite materials. And then it delves into a thorough exploration of strategies geared towards augmenting performance, encompassing the introduction of electron donor-acceptor (D-A) units, heteroatom doping, defect Engineering, architecture of Heterojunction and optimization of morphology. Following this, it systematically elucidates applications primarily centered around the efficient generation of photocatalytic hydrogen, reduction of carbon dioxide through photocatalysis, and the degradation of organic pollutants. Ultimately, the discourse turns towards unresolved challenges and the prospects for further advancement, offering valuable guidance for the potent harnessing of CTFs in high-efficiency photocatalytic processes.

Triazine and Fused Thiophene-Based Donor-Acceptor Type Semiconducting Conjugated Polymer for Enhanced Visible-Light-Induced H2 Production

Conjugated polymers have attracted significant attention in the field of photocatalysis due to their exceptional properties, including versatile optimization, cost-effectiveness, and structure stability. Herein, two conjugated porous polymers, PhIN-CPP and ThIN-CPP, based on triazines, were meticulously designed and successfully synthesized using benzene and thiophene as building blocks. Based on UV diffuse reflection spectra, the photonic band gaps of PhIN-CPP and ThIN-CPP were calculated as 2.05 eV and 1.79 eV. The PhIN-CPP exhibited a high hydrogen evolution rate (HER) of 5359.92 μmol·g-1·h-1, which is 10 times higher than that of Thin-CPP (538.49 μmol·g-1·h-1). The remarkable disparity in the photocatalytic performance can be primarily ascribed to alterations in the band structure of the polymers, which includes its more stable benzene units, fluffier structure, larger specific surface area, most pronounced absorption occurring in the visible region and highly extended conjugation with a high density of electrons. The ΔEST values for PhIN-CPP and ThIN-CPP were calculated as 0.79 eV and 0.80 eV, respectively, based on DFT and TD-DFT calculations, which revealed that the incorporation of triazine units in the as-prepared CMPs could enhance the charge transfer via S1 ↔ T1 and was beneficial to the photocatalytic decomposition of H2O. This study presents a novel concept for developing a hybrid system for preparation of H2 by photocatalysis with effectiveness, sustainability, and economy.

Unveiling the exciton dissociation dynamics steered by built-in electric fields in conjugated microporous polymers for photoreduction of uranium (VI) from seawater

Developing highly efficient photocatalysts based on conjugated microporous polymers (CMPs) are often impeded by the intrinsically large exciton binding energy and sluggish charge transfer kinetics that result from their vulnerable driving force. Herein, a family of pyrene-based nitrogen-implanted CMPs were constructed, where the nitrogen gradient was regulated. Accordingly, the built-in electric field endowed by the nitrogen gradient dramatically accelerates the dissociation of exciton into free carriers, thereby enhancing charge separation efficiency. As a result, PyCMP-3N generated by polymerization of 1,3,6,8-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyrene and 2,4,6-tris(4-bromophenyl)-1,3,5-triazine featured an optimized built-in electric field and exhibited the highest photocatalytic removal efficiency of uranium (VI) (99.5 %). Our proposed strategy not only provides inspiration for constructing the built-in electric field by controlling nitrogen concentration gradients, but also offers an in-depth understanding the crucial role of built-in electric field in exciton dissociation and charge transfer, efficiently promoting CMPs photocatalysis.

Dye Modified Phenylenediamine Oligomers: Theoretical Studies on Drug Binding for Their Potential Application in Drug Sensors

The present work reports, for the first time, synthesis of dye incorporated o-phenylenediamine (OBB) with a view to obtain a conjugated oligomer with enhanced functionality. The structure was confirmed by IR studies, while the electronic transitions were confirmed by UV visible studies. The dye modified oligomer showed one order higher fluorescence intensity than the pristine Bismarck Brown (BB) dye. Confocal imaging showed red emission which could be utilized in near infra-red imaging. Density functional theory (DFT) studies were carried out to predict the theoretical properties of the oligomers. The energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital orbital were computed to explore how the HOMO energies of the reactants initiated the electronic interactions between them. The interaction energies were correlated to conjugation/hyper conjugation stabilization energies of the natural bond orbitals (NBO) via the DFT method using the B3LYP functional with the 6-311G(d) basis set on Gaussian 09 software. Drug binding was evaluated through simulation of interaction energy, (ΔEA-x) with drugs such as captopril, propranolol, thiazide, and fentanyl. The results predicted that the oligomer could be developed into a fentanyl drug sensor.