Molecular Dipole-Induced Photoredox Catalysis for Hydrogen Evolution over Self-Assembled Naphthalimide Nanoribbons

Large Dipole Moment Enhanced CO2 Adsorption on Copper Surface: Achieving 68.9% Catalytic Ethylene Faradaic Efficiency at 1.0 A cm-2

The electrochemical conversion of carbon dioxide (CO2) into hydrocarbon products emerges as a pivotal sustainable strategy for carbon utilization. Cu-based catalysts are currently prioritized as the most effective means for this process, yet it remains a long-term goal to achieve high product selectivity at elevated current densities. This study delved into exploring the influence of a topological poly(2-aminoazulene) with a substantial dipole moment on modulating the Cu surface dipole field to augment the catalytic activity involved in CO2 reduction. The resulting Cu/poly(2-aminoazulene) heterojunction showcases a remarkable ethylene Faradaic efficiency of 68.9% even at a substantial current density of 1 A cm-2. Through in situ Raman and in situ Fourier-transform infrared spectroscopy, poly(2-aminoazulene)-modified Cu electrode exhibits a heightened concentration of intermediates as compared to the bare Cu, proving advantageous for C-C dimerization. Theoretical calculations demonstrate the reduced energy barrier for C-C dimerization, and meanwhile impeding hydrogen evolution reaction on Cu/poly(2-aminoazulene) heterojunction, which are beneficial to CO2 reduction. The catalyst design in this study, incorporating dipole moment considerations, not only investigates the influence of dipole moment on electrochemical carbon dioxide reduction but also pioneers an innovative strategy to augment catalytic activity by elevating the micro-concentration of reactants on catalyst surfaces.

Precise Supramolecular Nanoarchitectonics for Simultaneous Enhanced Photoluminescence and Photocatalysis in a Co-Assembly by a Biomimetic Isolation-Conduction Strategy

Limited by the two mutually exclusive physicochemical processes of separation and recombination of photogenerated carriers, achieving photoluminescence and photocatalysis simultaneously is extremely challenging but essential for ever-growing complex issues and specialized scenarios. Here we proposed a biomimetic isolation-conduction strategy induced by an arene-perfluoroarene (A-P) interaction for enabling photoluminescence and photocatalytic hydrogen evolution reaction (HER) activity in the co-assembly of aromatic monomers and octafluoronapthalene (OFN). Inspired by the isolation-conduction effect of periodic isolation of myelin sheaths on the axons of vertebrate nerve fibers by node of Ranvier, we use OFN as a molecular isolator embedded in the aromatic monomers array to block the singlet-to-triplet pathway, while the enlarged intermolecular dipoles resulting from the A-P interactions facilitate the conduction of photogenerated carriers in the isolated regions. The resultant co-assembly exhibits an enhanced monomeric green emission compared to the corresponding monocomponent self-assembly with weak red emission. Meanwhile, it also has an enhanced photocatalytic HER performance with a rate of 2.45 mmol g-1 h-1, which is 15.2 times more than the self-assembled one. On this basis, a sequential fluoric wastewater reuse system that includes real-time fluorescence detection/removal of perfluorooctanoic acids and photocatalytic HER device is constructed.

Carbon Doping Regulates Charge Transfer Paths via a Type-II to S-Scheme Transformation to Improve Photocatalytic Performance

Designing S-scheme heterojunctions with enhanced interfacial interaction is an effective strategy for promoting the separation of photocarriers while maintaining strong photoredox capabilities. However, precisely tailoring the interfacial charge transport pathways between two contacted semiconductors remains a significant challenge due to the similar band alignment in type-II and S-scheme heterostructures. Herein, we report a facile and low-cost carbon doping strategy to smartly tune the charge transfer pathway via a type-II to S-scheme transformation for efficient photocatalytic H2 evolution and H2O2 synthesis. Density functional theory calculations combined with in situ XPS studies demonstrate that the Fermi level of MoO2 shifts from being higher than that of C3N4 to being lower after carbon doping, which drives the inversion of the internal electric field (IEF) direction between MoO2 and C3N4, thus enabling a transition from type-II MoO2/C3N4 heterojunctions to S-scheme C-MoO2/C3N4 heterojunctions. As a result, the optimal S-scheme C-MoO2/C3N4 heterojunctions exhibit a high H2 evolution rate of 16.2 mmol g-1 h-1 and a H2O2 production rate of 877 μmol g-1 h-1, notably surpassing those of the original C3N4 and type-II MoO2/C3N4 heterojunctions. This work provides valuable insights into the fabrication of C3N4 heterostructures and the control of electron migration pathways, thereby creating new possibilities for photocatalysis and optoelectronics applications.

Molecular Engineering of Methylated Sulfone-Based Covalent Organic Frameworks for Back-Reaction Inhibited Photocatalytic Overall Water Splitting

Solar-to-hydrogen (H2) and oxygen (O2) conversion via photocatalytic overall water splitting (OWS) holds great promise for a sustainable fuel economy, but has been challenged by the backward O2 reduction reaction (ORR) with favored proton-coupled electron transfer (PCET) dynamics. Here, we report that molecular engineering by methylation inhibits the backward ORR of molecular photocatalysts and enables efficient OWS process. As demonstrated by a benchmark sulfone-based covalent organic framework (COF) photocatalyst, the precise methylation of its O2 adsorption sites effectively blocks electron transfer and increases the barrier for hydrogen intermediate desorption that cooperatively obstructs the PCET process of ORR. Methylation also repels electrons to the neighboring photocatalytic sulfone group that promotes the forward H2 evolution. The resultant DS-COF achieves an impressive inhibition of about 70 % of the backward reaction and a three-fold enhancement of the OWS performance with a H2 evolution rate of 124.7 μmol h-1 g-1, ranking among the highest reported for organic-based photocatalysts. This work provides insights for engineering photocatalysts at the molecular level for efficient solar-to-fuel conversion.

Merging semi-crystallization and multispecies iodine intercalation at photo-redox interfaces for dual high-value synthesis

The artificial photocatalytic synthesis based on graphitic carbon nitride (g-C3N4) for H2O2 production is evolving rapidly. However, the simultaneous production of high-value products at electron and hole sites remains a great challenge. Here, we use transformable potassium iodide to obtain semi-crystalline g-C3N4 integrated with the I-/I3- redox shuttle mediators for efficient generation of H2O2 and benzaldehyde. The system demonstrates a prominent catalytic efficiency, with a benzaldehyde yield of 0.78 mol g-1 h-1 and an H2O2 yield of 62.52 mmol g-1 h-1. Such a constructed system can achieve an impressive 96.25% catalytic selectivity for 2e- oxygen reduction, surpassing previously reported systems. The mechanism study reveals that the strong crystal electric field from iodized salt enhances photo-generated charge carrier separation. The I-/I3- redox mediators significantly boost charge migration and continuous electron and proton supply for dual-channel catalytic synthesis. This groundbreaking work in photocatalytic co-production opens neoteric avenues for high-value synthesis.

Dual Function of Naphthalenediimide Supramolecular Photocatalyst with Giant Internal Electric Field for Efficient Hydrogen and Oxygen Evolution

Organic supramolecular photocatalysts have garnered widespread attention due to their adjustable structure and exceptional photocatalytic activity. Herein, a novel bis-dicarboxyphenyl-substituent naphthalenediimide self-assembly supramolecular photocatalyst (SA-NDI-BCOOH) with efficient dual-functional photocatalytic performance is successfully constructed. The large molecular dipole moment and short-range ordered stacking structure of SA-NDI-BCOOH synergistically create a giant internal electric field (IEF), resulting in a remarkable 6.7-fold increase in its charge separation efficiency. Additionally, the tetracarboxylic structure of SA-NDI-BCOOH greatly enhances its hydrophilicity. Thus, SA-NDI-BCOOH demonstrates efficient dual-functional activity for photocatalytic hydrogen and oxygen evolution, with rates of 372.8 and 3.8 µmol h-1, respectively. Meanwhile, a notable apparent quantum efficiency of 10.86% at 400 nm for hydrogen evolution is achieved, prominently surpassing many reported supramolecular photocatalysts. More importantly, with the help of dual co-catalysts, it exhibits photocatalytic overall water splitting activity with H2 and O2 evolution rates of 3.2 and 1.6 µmol h-1. Briefly, this work sheds light on enhancing the IEF by controlling the molecular polarity and stacking structure to dramatically improve the photocatalytic performance of supramolecular materials.

Enhancing Built-in Electric Fields via Molecular Symmetry Modulation in Supramolecular Photocatalysts for Highly Efficient Photocatalytic Hydrogen Evolution

Nature-inspired supramolecular self-assemblies are attractive photocatalysts, but their quantum yields are limited by poor charge separation and transportation. A promising strategy for efficient charge transfer is to enhance the built-in electric field by symmetry breaking. Herein, an unsymmetric protonation, N-heterocyclic π-conjugated anthrazoline-based supramolecular photocatalyst SA-DADK-H+ was developed. The unsymmetric protonation breaks the initial structural symmetry of DADK, resulting in ca. 50-fold increase in the molecular dipole, and facilitates efficient charge separation and transfer within SA-DADK-H+. The protonation process also creates numerous active sites for H2O adsorption, and serves as crucial proton relays, significantly improving the photocatalytic efficiency. Remarkably, SA-DADK-H+ exhibits an outstanding hydrogen evolution rate of 278.2 mmol g-1 h-1 and a remarkable apparent quantum efficiency of 25.1 % at 450 nm, placing it among the state-of-the-art performances in organic semiconductor photocatalysts. Furthermore, the versatility of the unsymmetric protonation approach has been successfully applied to four other photocatalysts, enhancing their photocatalytic performance by 39 to 533 times. These findings highlight the considerable potential of unsymmetric protonation induced symmetry breaking strategy in tailoring supramolecular photocatalysts for efficient solar-to-fuel production.

Efficient selective aerobic oxidation of sulfides by molecular dipole modulation in methylphosphate-substituted perylene diimide supramolecular polarization photocatalyst

Photocatalytic aerobic oxidation is a promising sustainable strategy for the selective organic synthesis of industrially valuable chemicals. However, the poor charge separation and insufficient molecular activation restrict the overall photocatalytic efficiency. To address these issues, we have developed a novel approach involving molecular dipole modulation and polar molecular self-assembly to modulate the built-in electric field (BEF) in perylene diimide (PDI) supramolecular polarization photocatalysts by adjusting the electronegativity of terminal substituents. The optimized methylphosphate-substituted PDI (P-PDIP) supramolecular system features the strongest BEF induced by its large molecular dipole, with an intensity 3.89 times higher than that observed in methylcarboxy-substituted PDI (P-PDIC) and 5.64 times higher than that observed in P-PDI. This significant enhancement in BEF generates a powerful driving force within P-PDIP, facilitating directional charge separation toward active sites. Additionally, the incorporation of methylphosphate groups improves the activation efficiency of O2 and thioether molecules, resulting in a remarkable photocatalytic performance for selective aerobic oxidation of sulfides into sulfoxide (up to 99.9% conversion and 99.8% selectivity). This study highlights that enhancing BEF through manipulating molecular dipoles can significantly improve photocatalytic activity, offering great potential for constructing efficient organic polarization photocatalysts in green chemistry and sustainable production.

High Efficiency and Low Roll-Off Pure-Red Perovskite LED Enabled by Simultaneously Inhibiting Auger and Trap Recombination of Quantum Dots

CsPbI3 perovskite quantum dots (QDs) could achieve pure-red emission by reducing their size, but the increased exciton binding energy (EB) and surface defects for the small-sized QDs (SQDs) cause severe Auger and trap recombinations, thus worsening their electroluminescence (EL) performance. Herein, we utilize the dangling bonds of the SQDs as a driving force to accelerate KI dissolution to solve its low solubility in nonpolar solvents, thereby allowing K+ and I- to bond to the surface of SQDs. The EB of the SQDs was decreased from 305 to 51 meV because of the attraction of K+ to electrons, meanwhile surface vacancies were passivated by K+ and I-. The Auger and trap recombinations were simultaneously suppressed by this difunctional ligand. The SQD-based light-emitting diode showed a stable pure-red EL peak of 639 nm, an external quantum efficiency of 25.1% with low roll-off, and a brightness of 5934 cd m-2.

Self-assembled π-conjugated chromophores: preparation of one- and two-dimensional nanostructures and their use in photocatalysis

Photocatalytic systems have attracted research interest as a clean approach to generate energy from abundant sunlight. In this context, developing efficient and robust photocatalytic structures is crucial. Recently, self-assembled organic chromophores have entered the stage as alternatives to both molecular systems and (in)organic semiconductors. Nanostructures made of self-assembled π-conjugated dyes offer, on the one hand, molecular customizability to tune their optoelectronic properties and activities and on the other hand, provide benefits from heterogeneous catalysis that include ease of separation, recyclability and improved photophysical properties. In this contribution, we present recent achievements in constructing supramolecular photocatalytic systems made of chromophores for applications in water splitting, H2O2 evolution, CO2 reduction, or environmental remediation. We discuss strategies that can be used to prepare ordered photocatalytic systems with an emphasis on the effect of packing between the dyes and the resulting photocatalytic activity. We further showcase supramolecular strategies that allow interfacing the organic nanostructures with co-catalysts, molecules, polymers, and (in)organic materials. The principles discussed here are the foundation for the utilization of these self-assembled materials in photocatalysis.

Molecular Heptazine-Triazine Junction over Carbon Nitride Frameworks for Artificial Photosynthesis of Hydrogen Peroxide

Revealing the photocatalytic mechanism between various junctions and catalytic activities has become a hotspot in photocatalytic systems. Herein, an internal molecular heptazine/triazine (H/T) junction in crystalline carbon nitride (HTCN) is constructed and devoted to selective two-electron oxygen reduction reaction (2e- ORR) for efficient hydrogen peroxide (H2 O2 ) production. In-situ X-ray diffraction spectra under various temperatures authenticate the successful formation of molecular H/T junction in HTCN during the calcining process rather than physically mixing. The increased surface photovoltage and transient photovoltage signals, and the decreased exciton binding energy undoubtably elucidate that an obvious increasement of carrier density and diffusion capability of photogenerated electrons are realized over HTCN. Additionally, the analyses of in situ photoirradiated Kelvin probe force microscopy and femto-second transient absorption spectra reveal the successful construction of the strong internal built-in-electric field and the existence of the majority of long-lived shallow trapped electrons associated with molecular H/T junction over HTCN, respectively. Benefiting from these, the photocatalytic results exhibit an incredible improvement (96.5-fold) for H2 O2 production. This novel work provides a comprehensive understanding of the long-lived reactive charges in molecular H/T junctions for strengthening the driving-force for photocatalytic H2 O2 production, which opens potential applications for enhancing PCN-based photocatalytic redox reactions.

Zwitterionic and Hydrophilic Vinylene-Linked Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Evolution

Developing effective synthetic strategies as well as broadening functionalities for zwitterionic materials that comprise moieties with equimolar cationic and anionic groups still remains a huge challenge. Herein, we develop two zwitterionic vinylene-linked covalent organic frameworks (Zi-VCOF-1 and Zi-VCOF-2) that are a type of novel hydrophilic material. Zi-VCOF-1 and Zi-VCOF-2 are obtained directly through the convenient Knoevenagel condensation of new sulfonic-pyridinium zwitterionic monomers with aromatic aldehyde derivatives. This is the first report on zwitterionic COFs being constructed by the bottom-up functionalization approach from predesigned zwitterionic monomers. Both Zi-VCOFs exhibit a high photocatalytic hydrogen evolution rate (HER) because of their appropriate optical property and outstanding hydrophilicity. Specifically, Zi-VCOF-1 and Zi-VCOF-2 show photocatalytic HER of 13,547 and 5057 μmol h-1 g-1, respectively. Interestingly, the photocatalytic HER of Zi-VCOF-1 is about 2.68 times of that of Zi-VCOF-2, although they differ by only one methyl group in sulfonic-pyridinium zwitterionic pairs. The photocatalytic HER of Zi-VCOF-1 is not only the highest in the vinylene-linked COFs but also outstanding among the most reported COFs. This is the first application of zwitterionic COFs for photocatalytic hydrogen evolution, which would open a new frontier in zwitterionic COFs and be helpful for the design of other photocatalytic materials.

Thiadiazole-Derived Covalent Organic Framework Macroscopic Ultralight Aerogel

Shaping covalent organic frameworks (COFs) into macroscopic objects for practical application remains a huge challenge. Herein, a new thiadiazole-derived COF macroscopic ultralight aerogel (NNS-VCOF) was prepared through acid-catalyzed aldol condensation between 2,5-dimethyl-1,3,4-thiadiazole and a tritopic aromatic aldehyde derivative. NNS-VCOF aerogel shows extremely low density (ca. 0.020 g cm^-3), excellent mechanical properties (compression modulus of 16.65 kPa), thermal insulation properties (low thermal conductivity of 0.03270 W m^-1 K^-1 at 25 °C), and flame retardancy (quickly self-extinguishing after ignition) due to its three-dimensional sponge-like architecture and special nitrogen heterocyclic framework. To our delight, NNS-VCOF aerogel not only can be used as an outstanding macroscopic material but also shows efficient photocatalytic hydrogen evolution properties in a powder state because of the superhydrophilicity and appropriate optical properties.

Rational Design of PDI-Based Linear Conjugated Polymers for Highly Effective and Long-Term Photocatalytic Oxygen Evolution

Constructed through relatively weak noncovalent forces, the stability of organic supramolecular materials has shown to be a challenge. Herein, the designing of a linear conjugated polymer is proposed through creating a chain polymer connected via bridging covalent bonds in one direction and retaining π-stacked aromatic columns in its orthogonal direction. Specifically, three analogs of linear conjugated polymers through tuning the aromatic core and its covalently linked moiety (bridging group) within the building block monomer are prepared. Cooperatively supported by strong π-π stacking interactions from the extended aromatic core of perylene and favorable dipole-dipole interactions from the bridging group, the as-expected high crystallinity, wide light absorption, and increased stability are successfully achieved for Oxamide-PDI (perylene diimide) through ordered molecular arrangement, and present a remarkable full-spectrum oxygen evolution rate of 5110.25 µmol g^-1  h^-1 without any cocatalyst. Notably, experimental and theoretical studies reveal that large internal dipole moments within Oxamide-PDI together with its ordered crystalline structure enable a robust built-in electric field for efficient charge carrier migration and separation. Moreover, density functional theory (DFT) calculations also reveal oxidative sites located at carbon atoms next to imide bonds and inner bay positions based on proven spatially separated photogenerated electrons and holes, thus resulting in highly efficient water photolysis into oxygen.

Photocatalytic Anaerobic Dehydrogenation of Alcohols over Metal Halide Perovskites: A New Acid-Free Scheme for H2 Production

Photocatalytic H₂ evolution from haloid acid (HX) solution by metal halide perovskites (MHPs) has been intensively investigated; however, the corrosive acid solution severely restricts its practical operability. Therefore, developing acid-free schemes for H₂ evolution using MHPs is highly desired. Here, we investigate the photocatalytic anaerobic dehydrogenation of alcohols over a series of MHPs (APbX₃, A = Cs⁺, CH₃NH₃⁺ (MA), CH(NH₂)₂⁺ (FA); X = Cl^-, Br^-, I^-) to simultaneously produce H₂ and aldehydes. Via the coassembly of Pt and rGO nanosheets on MAPbBr₃ microcrystals, the optimal MAPbBr₃/rGO-Pt reaches a H₂ evolution rate of 3150 μmol g^-1 h^-1 under visible light irradiation (780 nm ≥ λ ≥ 400 nm), which is more than 105-fold higher than pure MAPbBr₃ (30 μmol g^-1 h^-1). The present work not only brings new ample opportunities toward photocatalytic H₂ evolution but also opens up new avenues for more effective utilization of MHPs in photocatalysis.