Molecular Porous Photosystems Tailored for Long-Term Photocatalytic CO2 Reduction

The molecular-level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long-term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time-resolved spectroscopy.     

Surface Architectures Built around Perylenediimide Stacks

Simple stacks of perylenediimides (PDIs) grown directly on solid surfaces are an intriguing starting point for the construction of multicomponent architectures because their intrinsic activity is already very high. The ability of PDI stacks to efficiently generate photocurrent originates from the strong absorption of visible light and the efficient transport of both electrons and holes after generation with light. The objective of this study was to explore whether or not the excellent performance of these remarkably simple single‐channel photosystems could be further improved in more sophisticated multicomponent architectures. We report that the directional construction of strings of anions or cations along the PDI stacks does not significantly improve their activity; that is, the intrinsic activity of PDI stacks is too high to yield ion‐gated photosystems. The directional construction of electron‐ and hole‐transporting stacks of naphthalenediimides (NDIs) and oligothiophenes along the central PDI stack did not improve photocurrent generation under standard conditions either. However, the activity of double‐channel photosystems increased with increasing thickness, whereas increasing charge recombination with single‐channel PDI stacks resulted in decreasing activity with increasing length. Most efficient long‐distance charge transport was found with double‐channel photosystems composed of PDIs and NDIs. This finding suggests that over long distances, PDI stacks transport holes better than electrons, at least under the present conditions. Triple‐channel photosystems built around PDI stacks with oligothiophenes and triphenylamines were less active, presumably because hole mobility in the added channels was inferior to that in the original PDI stacks, thus promoting charge recombination.     

Aerobic Asymmetric Dehydrogenative Cross‐Coupling between Two CH Groups Catalyzed by a Chiral‐at‐Metal Rhodium Complex

A sustainable C? C bond formation is merged with the catalytic asymmetric generation of one or two stereocenters. The introduced catalytic asymmetric cross‐coupling of two C? H groups with molecular oxygen as the oxidant profits from the oxidative robustness of a chiral‐at‐metal rhodium(III) catalyst and exploits an autoxidation mechanism or visible‐light photosensitized oxidation. In the latter case, the catalyst serves a dual function, namely as a chiral Lewis acid for catalyzing enantioselective enolate chemistry and at the same time as a visible‐light‐driven photoredox catalyst.     

Supramolecular photocatalyst of Palladium (II) Encapsulated within Dendrimer on TiO2 nanoparticles for Photo‐induced Suzuki‐Miyaura and Sonogashira Cross‐Coupling reactions

In this study, synthesis, characterization and catalytic performance of a novel supramolecular photocatalytic system including palladium (II) encapsulated within amine‐terminated poly (triazine‐triamine) dendrimer modified TiO₂ nanoparticles (Pd (II) [PTATAD] @ TiO₂) is presented. The obtained nanodendritic catalyst was characterized by FT‐IR, ICP‐AES, XPS, EDS, TEM, TGA and UV‐DRS. The as‐prepared nanodendritic catalyst was shown to be highly active, selective, and recyclable for the Suzuki–Miyaura and Sonogashira cross‐coupling of a wide range of aryl halides including electron‐rich and electron‐poor and even aryl chlorides, affording the corresponding biaryl compounds in good to excellent yields under visible light irradiation. This study shows that visible light irradiation can drive the cross‐coupling reactions on the Pd (II) [PTATAD] @ TiO₂ under mild reaction conditions (27–30 °C) and no additional additives such as cocatalysts or phosphine ligands. So, we propose that the improved photoactivity predominantly benefits from the synergistic effects of Pd (II) amine‐terminated poly (triazine‐triamine) dendrimer on TiO₂ nanoparticles that cause efficient separation and photogenerated electron–hole pairs and photoredox capability of nanocatalyst which all of these advantages due to the tuning of band gap of catalyst in the visible light region.     

BiOCl/In2S3复合可见光催化剂制备及性能研究

氯氧化铋（BiOCl）较大的禁带宽度使得其只能对紫外光产生响应,严重制约了其进一步光催化应用。为实现BiOCl对可见光的利用,以In2S3为可见光光敏剂,并基于高效实用的机械研磨手段构建BiOCl/In2S3复合可见光催化剂。通过扫描电子显微镜(SEM)、X射线衍射(EDS)、X射线衍射(XRD)、红外光谱(FT-IR)和紫外-可见漫反射光谱(UV-Vis DRS)等方法对催化剂的形貌和结构进行表征。选择盐酸四环素（TC）可见光催化降解为评价模型,系统研究了BiOCl/In2S3复合比例对光催化活性的影响。结果表明两者复合比例为1:1时具有最佳的光催化活性,在可见光照射下对TC的降解效率高达91.4%,且经3次循环降解效率仍保持在87.3%。机理研究表明,In2S3被可见光激发产生电子注入BiOCl的导带(CB),能有效提升载流子的分离效率,而h+和?O2-是光降解过程中的主要活性物质。该项研究工作充分表明了In2S3对BiOCl的高效光敏活性,展示了物理复合法在新型高效可见光催化体系构建中的重要意义。     

Visible‐Light‐Triggered Drug Release from TiO2 Nanotube Arrays: A Controllable Antibacterial Platform

In this work, we use a double‐layered stack of TiO₂ nanotubes (TiNTs) to construct a visible‐light‐triggered drug delivery system. The key for visible light drug release is a hydrophobic cap on the nanotubes containing Au nanoparticles (AuNPs). The AuNPs allow for a photocatalytic scission of the hydrophobic chain under visible light. To demonstrate this principle, we loaded ampicillin (AMP) into the lower part of the TiO₂ nanotube stack, triggered visible‐light‐induced release, and carried out antibacterial studies. The release from the platform becomes most controllable if the drug is silane‐grafted in the hydrophilic bottom layer for drug storage. Thus, visible light photocatalysis can also determine the release kinetics of the active drug from the nanotube wall.     

Aerobic Asymmetric Dehydrogenative Cross‐Coupling between Two C?H Groups Catalyzed by a Chiral‐at‐Metal Rhodium Complex

A sustainable C C bond formation is merged with the catalytic asymmetric generation of one or two stereocenters. The introduced catalytic asymmetric cross‐coupling of two C H groups with molecular oxygen as the oxidant profits from the oxidative robustness of a chiral‐at‐metal rhodium(III) catalyst and exploits an autoxidation mechanism or visible‐light photosensitized oxidation. In the latter case, the catalyst serves a dual function, namely as a chiral Lewis acid for catalyzing enantioselective enolate chemistry and at the same time as a visible‐light‐driven photoredox catalyst.     

Reactivation of a Poisoned Metallocene Catalyst by Irradiation with Visible Light

Both oxygen and carbon dioxide are efficient catalyst poisons, remarkably reducing the ethylene polymerisation rate, increasing the molecular weight of the resulting polyethylene, and broadening its molecular weight distribution (MWD). By introducing visible light into the contaminated polymerisation system, the catalyst activity was totally recovered. The molecular weight and MWD became similar to those of a non‐poisoned system, supporting the formation of new active sites during poisoning that are responsible for the lower activity and broader MWD.     

Visible‐Light Photochemical Reduction of CO2 to CO Coupled to Hydrocarbon Dehydrogenation

Research on the photochemical reduction of CO₂, initiated already 40 years ago, has with few exceptions been performed by using amines as sacrificial reductants. Hydrocarbons are high‐volume chemicals whose dehydrogenation is of interest, so the coupling of a CO₂ photoreduction to a hydrocarbon‐photodehydrogenation reaction seems a worthwhile concept to explore. A three‐component construct was prepared including graphitic carbon nitride (g‐CN) as a visible‐light photoactive semiconductor, a polyoxometalate (POM) that functions as an electron acceptor to improve hole–electron charge separation, and an electron donor to a rhenium‐based CO₂ reduction catalyst. Upon photoactivation of g‐CN, a cascade is initiated by dehydrogenation of hydrocarbons coupled to the reduction of the polyoxometalate. Visible‐light photoexcitation of the reduced polyoxometalate enables electron transfer to the rhenium‐based catalyst active for the selective reduction of CO₂ to CO. The construct was characterized by zeta potential, IR spectroscopy, thermogravimetry, scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS). An experimental Z‐scheme diagram is presented based on electrochemical measurements and UV/Vis spectroscopy. The conceptual advance should promote study into more active systems.     

Molecular Semiconductor Surfactants with Fullerenol Heads and Colored Tails for Carbon Dioxide Photoconversion

The leaf is a prime example of a material converting waste (CO₂) into value with maximum sustainability. As the most important constituent, it contains the coupled photosystems II and I, which are imbedded in the cellular membrane of the chloroplasts. Can key functions of the leaf be packed into soap? We present next‐generation surfactants that self‐assemble into bilayer vesicles (similar to the cellular membrane), are able to absorb photons of two different visible wavelengths, and exchange excited charge carriers (similar to the photosystems), followed by conversion of CO₂ (in analogy to the leaf). The amphiphiles contain five dye molecules as the hydrophobic entity attached exclusively to one hemisphere of a polyhydroxylated fullerene (Janus‐type). We herein report on their surfactant, optical, electronic, and catalytic properties. Photons absorbed by the dyes are transferred to the fullerenol head, where they can react with different species such as CO₂ to give formic acid.     

Chemical‐Bond‐Mediated p–n Heterojunction Photocatalyst Constructed from Coordination Polymer Nanoparticles and a Conducting Copolymer: Visible‐Light Active and Highly Efficient

A visible‐light‐active p–n heterojunction photocatalyst has been synthesized by the enwrapping of poly[aniline‐co‐N‐(4‐sulfophenyl)aniline] ( PAPSA ) on a coordination polymer nanoparticle ( NCP ). Compared with the visible‐light‐inactive NCP , the new p–n heterojunction photocatalyst, PAPSA/NCP , exhibits a much higher efficiency in the reduction of Cr^VI under visible light. PAPSA performs two functions in this p–n heterojunction photocatalyst. First, as a visible‐light‐active material, it extends the photoresponse region of the photocatalyst from the ultraviolet to the visible‐light region. Secondly, as a p‐type semiconductor possessing suitable energy levels with respect to NCP , PAPSA forms a p–n heterojunction with the n‐type NCP ; the inner electric field of the p–n heterojunction accelerates the separation of electrons and holes, which enhances the photocatalytic efficiency. Furthermore, the p–n heterojunction photocatalyst exhibits outstanding stability during the photocatalytic reduction of Cr^VI.     

Asymmetric Covalent Triazine Framework for Enhanced Visible‐Light Photoredox Catalysis via Energy Transfer Cascade

Complex multiple‐component semiconductor photocatalysts can be constructed that display enhanced catalytic efficiency via multiple charge and energy transfer, mimicking photosystems in nature. In contrast, the efficiency of single‐component semiconductor photocatalysts is usually limited due to the fast recombination of the photogenerated excitons. Here, we report the design of an asymmetric covalent triazine framework as an efficient organic single‐component semiconductor photocatalyst. Four different molecular donor–acceptor domains are obtained within the network, leading to enhanced photogenerated charge separation via an intramolecular energy transfer cascade. The photocatalytic efficiency of the asymmetric covalent triazine framework is superior to that of its symmetric counterparts; this was demonstrated by the visible‐light‐driven formation of benzophosphole oxides from diphenylphosphine oxide and diphenylacetylene.     

Formation of Hierarchical FeCoS2–CoS2 Double‐Shelled Nanotubes with Enhanced Performance for Photocatalytic Reduction of CO2

Hierarchical FeCoS₂–CoS₂ double‐shelled nanotubes have been rationally designed and constructed for efficient photocatalytic CO₂ reduction under visible light. The synthetic strategy, engaging the two‐step cation‐exchange reactions, precisely integrates two metal sulfides into a double‐shelled tubular heterostructure with both of the shells assembled from ultrathin two‐dimensional (2D) nanosheets. Benefiting from the distinctive structure and composition, the FeCoS₂–CoS₂ hybrid can reduce bulk‐to‐surface diffusion length of photoexcited charge carriers to facilitate their separation. Furthermore, this hybrid structure can expose abundant active sites for enhancing CO₂ adsorption and surface‐dependent redox reactions, and harvest incident solar irradiation more efficiently by light scattering in the complex interior. As a result, these hierarchical FeCoS₂–CoS₂ double‐shelled nanotubes exhibit superior activity and high stability for photosensitized deoxygenative CO₂ reduction, affording a high CO‐generating rate of 28.1 μmol h^?1 (per 0.5 mg of catalyst).     

Asymmetric Photocatalysis by Intramolecular Hydrogen‐Atom Transfer in Photoexcited Catalyst–Substrate Complex

3‐(2‐Formylphenyl)‐1‐pyrazol‐1‐yl‐propenones undergo an asymmetric photorearrangement to benzo[d]cyclopropa[b]pyranones with up to >99 % ee, which is catalyzed by a bis‐cyclometalated rhodium catalyst in the presence of visible light. Mechanistic experiments and DFT calculations support a mechanism in which a photoexcited catalyst/substrate complex triggers an intramolecular hydrogen‐atom transfer followed by a highly stereocontrolled hetero‐Diels–Alder reaction. In this reaction scheme, the rhodium catalyst fulfills multiple functions by 1) enabling visible‐light π→π* excitation of the catalyst‐bound enone substrate, 2) facilitating the hydrogen‐atom transfer, and 3) providing the asymmetric induction for the hetero‐Diels–Alder reaction.     

Enhanced Photocatalytic Hydrogen Evolution over Hierarchical Composites of ZnIn2S4 Nanosheets Grown on MoS2 Slices

A highly active hierarchical MoS₂/ZnIn₂S₄ composite catalyst was synthesized in situ by using a facile controlled‐growth approach through a solvothermal process. During the solvothermal reaction, 2D ultrathin curled ZnIn₂S₄ nanosheets grew on the surface of MoS₂ slices, which could help to form a more‐homogeneous mixture, effective interfacial contact, and strong interactions between the ZnIn₂S₄ nanosheets and the MoS₂ slices. The intimate contact between ZnIn₂S₄ and MoS₂ favored the formation of junctions between the two components, thereby improving the charge separation and prolonging the mean lifetime of the electron–hole pairs. Moreover, growing ZnIn₂S₄ nanosheets by visible‐light catalysis on MoS₂ slices afforded a higher number of available catalytically active sites. So, the photocatalytic hydrogen‐evolution performance of the hierarchical MoS₂/ZnIn₂S₄ composite was significantly enhanced, owing to a synergistic effect of these factors. This work could provide new insights into the fabrication of a highly efficient and low‐cost non‐noble‐metal co‐catalyst for visible‐light H₂ generation.     

Integration of Plasmonic Effects and Schottky Junctions into Metal–Organic Framework Composites: Steering Charge Flow for Enhanced Visible‐Light Photocatalysis

A wide range of light absorption and rapid electron–hole separation are desired for efficient photocatalysis. Herein, on the basis of a semiconductor‐like metal–organic framework (MOF), a Pt@MOF/Au catalyst with two types of metal–MOF interfaces integrates the surface plasmon resonance excitation of Au nanorods with a Pt‐MOF Schottky junction, which not only extends the light absorption of the MOF from the UV to the visible region but also greatly accelerates charge transfer. The spatial separation of Pt and Au particles by the MOF further steers the formation of charge flow and expedites the charge migration. As a result, the Pt@MOF/Au presents an exceptionally high photocatalytic H₂ production rate by water splitting under visible light irradiation, far superior to Pt/MOF/Au, MOF/Au and other counterparts with similar Pt or Au contents, highlighting the important role of each component and the Pt location in the catalyst.     

Electrophotocatalysis with a Trisaminocyclopropenium Radical Dication

Visible‐light photocatalysis and electrocatalysis are two powerful strategies for the promotion of chemical reactions. Here, these two modalities are combined in an electrophotocatalytic oxidation platform. This chemistry employs a trisaminocyclopropenium (TAC) ion catalyst, which is electrochemically oxidized to form a cyclopropenium radical dication intermediate. The radical dication undergoes photoexcitation with visible light to produce an excited‐state species with oxidizing power (3.33 V vs. SCE) sufficient to oxidize benzene and halogenated benzenes via single‐electron transfer (SET), resulting in C?H/N?H coupling with azoles. A rationale for the strongly oxidizing behavior of the photoexcited species is provided, while the stability of the catalyst is rationalized by a particular conformation of the cis‐2,6‐dimethylpiperidine moieties.     

Visible‐Light‐Promoted Iminyl‐Radical Formation from Acyl Oximes: A Unified Approach to Pyridines,Quinolines, and Phenanthridines

A unified strategy involving visible‐light‐induced iminyl‐radical formation has been established for the construction of pyridines, quinolines, and phenanthridines from acyl oximes. With fac‐[Ir(ppy)₃] as a photoredox catalyst, the acyl oximes were converted by 1 e⁻ reduction into iminyl radical intermediates, which then underwent intramolecular homolytic aromatic substitution (HAS) to give the N‐containing arenes. These reactions proceeded with a broad range of substrates at room temperature in high yield. This strategy of visible‐light‐induced iminyl‐radical formation was successfully applied to a five‐step concise synthesis of benzo[c]phenanthridine alkaloids.     

Visible‐Light‐Promoted Iminyl‐Radical Formation from Acyl Oximes: A Unified Approach to Pyridines,Quinolines, and Phenanthridines

A unified strategy involving visible‐light‐induced iminyl‐radical formation has been established for the construction of pyridines, quinolines, and phenanthridines from acyl oximes. With fac‐[Ir(ppy)₃] as a photoredox catalyst, the acyl oximes were converted by 1 e^? reduction into iminyl radical intermediates, which then underwent intramolecular homolytic aromatic substitution (HAS) to give the N‐containing arenes. These reactions proceeded with a broad range of substrates at room temperature in high yield. This strategy of visible‐light‐induced iminyl‐radical formation was successfully applied to a five‐step concise synthesis of benzo[c]phenanthridine alkaloids.     

Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using ‘Ene’‐Reductases with Photoredox Catalysts

Flavin‐dependent ‘ene’‐reductases (EREDs) are highly selective catalysts for the asymmetric reduction of activated alkenes. This function is, however, limited to enones, enoates, and nitroalkenes using the native hydride transfer mechanism. Here we demonstrate that EREDs can reduce vinyl pyridines when irradiated with visible light in the presence of a photoredox catalyst. Experimental evidence suggests the reaction proceeds via a radical mechanism where the vinyl pyridine is reduced to the corresponding neutral benzylic radical in solution. DFT calculations reveal this radical to be “dynamically stable”, suggesting it is sufficiently long‐lived to diffuse into the enzyme active site for stereoselective hydrogen atom transfer. This reduction mechanism is distinct from the native one, highlighting the opportunity to expand the synthetic capabilities of existing enzyme platforms by exploiting new mechanistic models.