Photogeneration Of Radicals Research Articles

Coherent manipulation of photochemical spin-triplet formation in quantum dot-molecule hybrids.

The interconversion between singlet and triplet spin states of photogenerated radical pairs is a genuine quantum process, which can be harnessed to coherently manipulate the recombination products through a magnetic field. This control is central to such diverse fields as molecular optoelectronics, quantum sensing, quantum biology and spin chemistry, but its effect is typically fairly weak in pure molecular systems. Here we introduce hybrid radical pairs constructed from semiconductor quantum dots and organic molecules. The large g-factor difference enables us to directly observe the radical-pair spin quantum beats usually hidden in previous studies, which are further accelerated by the strong exchange coupling of radical pairs enabled by the quantum confinement of quantum dots. The rapid quantum beats enable the efficient and coherent control of charge recombination dynamics at room temperature, with the modulation level of the yield of spin-triplet products reaching 400%.

Chain assembly of Rhodococcus bacteria with O-doped g-C3N4 for photocatalysis mediated high-performance partial nitrification: From nitrite resource evolution to device application.

Nitrogen conversion via partial nitrification-anammox (PN/A), utilizing nitrite as a key intermediate, is an ideal low-carbon approach for wastewater nitrogen removal. However, the partial nitrification process, which is rate-limited and relies on less common bacteria with slow reaction kinetics, poses challenges for high-throughput PN/A implementation. Herein, we developed a microbial/photocatalysis coupling system using Rhodococcus bacterial and O-doped g-C3N4 (OCN) photocatalysts. This approach leverages photogenerated electrons and free radicals from photocatalysts to directly activate microorganisms, enhancing the redox gradient. This intensification selectively inhibits the enzymatic conversion of nitrite to nitrate and its reduction to nitrogen in Rhodococcus bacteria. Consequently, it promotes a highly selective partial nitrification process, generating ample nitrite to facilitate anammox reactions. Transmission electron microscopy and electrochemical characterization showed bacteria forming chain-like assemblies on OCN particles, with the composite exhibiting a favorable redox profile, low impedance, and high stability. Ammonia conversion to nitrite reached 96 % in 3 days, with an enriched NO2- concentration of 36.3 mg/L, 10 times higher than the raw bacterial control. Hence, this strategy of constructing bacterial-photocatalysis system achieved high selectivity and efficiency in partial nitrification. Transcriptome and qPCR analyses showed upregulation of genes linked to the short-cut denitrification metabolic pathway. Photocatalyst band structure and redox potential analysis suggest a new bio-photoelectrochemical partial nitrification pathway. Finally, the feasibility and applicability in future industrial and ecological water treatment were validated through demo H-type reactors and aquarium experiments. These findings offer innovative perspectives for controlled modulation of ammonia nitrogen conversion focus on nitrite intermediate, advancing an energy-efficient, low-carbon nitrogen cycle.

Correlation between spin-dependent recombination centers and long-lived polarons generated in organic photovoltaic devices revealed by successive ESR and EDMR measurements

Using a successive detection technique with electron spin resonance (ESR) and electrically detected magnetic resonance (EDMR), this study clarifies the quantitative correlation between photoinduced spin amounts and spin-dependent recombination (SDR) currents in organic photovoltaic devices (OPVs). Using this unique method of sequentially switching between ESR and EDMR measurements under light irradiation, we find that the intensities of light-induced ESR and EDMR spectra increase along with the light irradiation power. Although positive correlation exists between the number of photo-generated radicals and the SDR currents, the relation is not proportional, which demonstrates that most of the photo-generated radicals are residual accumulated charges. Additionally, phases of the EDMR spectra under light irradiation were found to be changed because of a delay of modulated EDMR signals. The phase variation is probably caused by recombination centers: positive polarons that have arrived at the interface between an aluminum electrode and an active layer by charge drifting after charge separation. Because positive polarons are expected to transport positive charges to the opposite-side electrode of the aluminum as a negative charge collector, this leakage current can be a factor of disturbing an optimal charge collection. This combined technique of ESR and EDMR is useful to explore the different roles of polarons in the photovoltaic conversion processes, thereby providing important information for improving the fill factors and open-circuit voltages of the OPVs, which generate long-lived polarons.

Room-Temperature Quantum Coherence of Reversible Photo-Generated Radical and its Film.

Electron spin qubits are becoming an important research direction in the field of quantum computing and information storage. However, the quantum decoherence has seriously hindered the development of this field. So far, few qubits exhibit long phase memory time (Tm), and even fewer qubits that can reach room temperature. Some reports show that the coherence times of radicals are generally long, so radicals may be the preferred spin carriers for qubits. Here, we demonstrate the qubit properties of a photogenerated radical (1 a) based on 2,4,6-Tri(4-pyridyl)-1,3,5-triazine (tpt, 1). More importantly, the photogenerated radical is a spin self-diluting complex, which the dilution is generally used in the investigation of qubits to reduce the interference of environment on qubits in order to overcome the decoherence of qubits. It is surprised that radical tpt has a stable Tm=1.1 μs above 20 K, even keep it to room temperature. In addition, the tpt-film prepared by the vacuum evaporation is significantly increase the T1 and Tm at low temperature.

Photo-Induced Ultrafast Charge Transfer and Air-Stable Radical Formation in Tetraphenylpyrene Derivatives.

Stable organic radicals generated by photo-excitation hold applications in molecular switching devices and information storage. It remains challenging to develop photo-generated radical materials with rapid response and air stability in the solid state. Here, we report a structure based on 1,3,6,8-tetraphenylpyrene derivative (Py-TTAc) displaying photo-induced radicals with air stability in the solid state. Photo-induced electron transfer, exposed to a 365 nm ultraviolet lamp for 1 minute, affords radicals in Py-TTAc powder as confirmed by electron paramagnetic resonance (EPR) spectroscopy. The maximum radical concentration reaches 2.21 % after continuous irradiation for 1 hour and recurs more than 10 times without any chemical degradation. The mechanistic study according to the femtosecond transient absorption (fsTA) and X-ray technology suggests that the radicals are derived from photo-induced symmetry-breaking charge separation (SB-CS) and stabilized through non-covalent interactions. The photo-generated stable radical system is employed in anti-counterfeiting paper and optoelectronic device applications. This study will provide insights into the development of photoactive organic radical materials.

Photocatalytic Methane Oxidation and Removal Mediated by Free Radicals

Activation and selective oxidation of C-H bond in methane under mild conditions constitutes long-standing challenges which are of fundamental and technological importance, from biological to industrial and environmental. Earth relies on free radicals to remove the climate-damaging methane and other organic pollutants from the air. In recent decades, intensive efforts have been focused on leveraging free radicals for selective methane oxidation. Free radicals are one of key mediators underpinning many active sites in thermal catalysis and these enhancement effects induced by the light and electric fields. However, it remains unclear how free radicals as active species mediate the C-H bond activation in methane and dictate the products distribution.In this talk, we will discuss our recent advances in understanding and promoting the photocatalytic oxidation of methane to methanol by combining the rational design of photocatalysts, photochemical experiments, as well as the in-situ electron paramagnetic resonance studies of free radicals. Our results unravel interactions between these free radicals and the solid co-catalysts, ions, and gases molecules in water, as well as their impact on methane removal and its selective oxidation. Our studies highlight the neglected while important interplay between photogenerated radicals and co-catalysts, ion impurities, and gas molecules in promoting methane removal and controlling the products distribution. Furthermore, we report an inherent trade-off in the photochemical methane to methanol conversion. A new design principle featuring isolating different reaction steps is developed to circumvent this trade-off.Such molecular-level insights into photocatalysts and their interactions with free radicals are expected to promote the methane removal and its selective functionalization and offer informative design principles for chemical bonds activations that are driven by light, heat, and electric fields.

Rh-Catalyzed Asymmetric Allylic Substitution with Photo-Generated Alkyl Radical Species

Rh-Catalyzed Asymmetric Allylic Substitution with Photo-Generated Alkyl Radical Species

Depolymerization of Native Lignin over Thiol Capped Ultrathin ZnIn2S4 Microbelts Mediated by Photogenerated Thiyl Radical

AbstractThe valorization of native lignin to functionalized aromatic compounds under visible light is appealing yet challenging. In this communication, colloidal mercaptoalkanoic acid capped ultrathin ZnIn2S4 (ZIS) microbelts was successfully fabricated, which was used as a superior catalyst for depolymerization of native lignin in birch woodmeal under visible light, with an optimum yield of 28.8 wt % to functionalized aromatic monomers achieved in 8 h. The capped mercaptoalkanoic acid not only enables a solvent modulated reversible interchange of ZIS between the colloidal state for efficient reaction and the aggregated state for facile separation, but also serves as a precursor for light initiated generation of reactive thiyl radical for highly selective cleavage of β‐O‐4 bond in native lignin. This work provides a green and efficient strategy for the depolymerization of native lignin to functionalized aromatic monomers under mild conditions, which involves a new mechanism for the cleavage of β‐O‐4 bonds in native lignin. The capability of cleavage of β‐O‐4 bonds in native lignin by photogenerated thiyl radicals also demonstrates the great potential of using photogenerated thiyl radicals in organics transformations.

Supramolecular Chiral Aggregation of Porphyrin Induced by Photo-Generated Triphenylamines Radical Cations.

Here, it is shown that photoirradiation triggered chiral J-aggregates formation of an achiral anionic porphyrin, TPPS (tetrakis(4-sulfonatophenyl) porphyrin), in the presence of chiral triphenylamine (TPA) derivatives. A series of chiral triarylamines linked with aromatic rings is designed through urea or amide bonds. UV-irradiation of self-assembled urea-linked triphenylamine derivatives causes the formation of persistent radical cations in the chlorinated solvents, which subsequently induces the aggregation of TPPS. Transferring chirality of TPA derivatives to achiral TPPS J-aggregates leads to the chiral assemblies with remarkable chiroptical signals. The experimental results demonstrate that, TPA derivatives linked by the urea bond can effectively promote the aggregation of TPPS rather than those with the amide bond although the photo-generated radical cations are both produced. It is suggested that the urea-linked TPA derivatives are more favorable to stable radical cations and thus cause the formation of TPPS chiral J-aggregation. This work may open up an avenue for designing photo-modulated chiral supramolecular assemblies.

Synthesis of SnO2/SrTiO3 composite and photocatalytic activity for methylene blue degradation under sunlight

In this study, the SnO2/SrTiO3 composite has been fabricated by, firstly preparing SnO2 and SrTiO3 through, followed by coupling SnO2 and SrTiO3 by the hydrothermal method at 180 oC for 24 hours. The obtained materials were characterized by X-Ray diffraction (XRD), Fourier transformation infrared spectra (FT-IR), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM). The photocatalytic activity of composite was assessed by degradation of methylene blue in water under sunlight. The composite exhibits a good photocatalytic activity compared to individual components (SnO2 and SrTiO3). An enhancement in photocatalytic activity of the composite with the presence of SnO2 has been observed. 1,4-benzoquinone (BQ) và tert-butyl alcohol (TBA) were used as quenchers for trapping photogenerated superoxide radical anions (•O2-) and hydroxyl radicals (•OH), respectively. In the presence of the quenchers, the photocatalytic activity of the composite has decreased significantly.

Zero-dimensional halide hybrid bulk glass exhibiting reversible photochromic ultralong phosphorescence

Dynamically responsive materials, capable of reversible changes in color appearance and/or photoemission upon external stimuli, have attracted substantial attention across various fields. This study presents an effective approach wherein switchable modulation of photochromism and ultralong phosphorescence can be achieved simultaneously in a zero-dimensional organic-inorganic halide hybrid glass doped with 4,4´-bipyridine. The facile fabrication of large-scale glasses is accomplished through a combined grinding-melting-quenching process. The persistent luminescence can be regulated through the photochromic switch induced by photo-generated radicals. Furthermore, the incorporation of the aggregation-induced chirality effect generates intriguing circularly polarized luminescence, with an optical dissymmetry factor (glum) reaching the order of 10–2. Exploiting the dynamic ultralong phosphorescence, this work further achieves promising applications, such as three-dimensional optical storage, rewritable photo-patterning, and multi-mode anti-counterfeiting with ease. Therefore, this study introduces a smart hybrid glass platform as a new photo-responsive switchable system, offering versatility for a wide array of photonic applications.

A Hexaarylbiimidazole‐Terarylene Hybrid: Visible‐to‐NIR‐II Absorption via Sequential Photochromic Reactions

A synergetic interaction between two or more photochromic chromophores has a potential to achieve advanced photochemical properties beyond conventional photochromic molecules and to realize photochemical control of complex systems using only a single molecule. Herein, we report a hybrid photochromic molecule consisting of hexaarylbiimidazole (HABI) and terarylene that exhibits multi‐state photochromism. The biphotochrome hybrid shows four‐state photochromic reaction involving sequentially proceeding photoreactions. The UV or visible light irradiation to the biphotochrome leads to the C–N bond breaking reaction of the HABI in preference to the ring‐closing reaction of the 6π‐electron system in the terarylene unit, leading two terarylene radical molecules. The photogenerated terarylene radical further exhibits the 6π‐electrocyclization reaction by UV irradiation. The delocalized π‐radical on the closed‐ring form of the terarylene is efficient to enhance the photosensitivity to the NIR‐I and ‐II region. Furthermore, a recombination reaction of radicals between the open‐ and closed‐ring isomers of terarylene affords an unprecedented photochromic dimer as a structural isomer of the initial molecule. This is a consequence of the sequential hybrid photochromic system involving the HABI and terarylene units.

Depolymerization of Native Lignin over Thiol Capped Ultrathin ZnIn2S4 Microbelts Mediated by Photogenerated Thiyl Radical.

The valorization of native lignin to functionalized aromatic compounds under visible light is appealing yet challenging. In this communication, colloidal mercaptoalkanoic acid capped ultrathin ZnIn2S4 (ZIS) microbelts was successfully fabricated, which was used as a superior catalyst for depolymerization of native lignin in birch woodmeal under visible light, with an optimum yield of 28.8 wt % to functionalized aromatic monomers achieved in 8 h. The capped mercaptoalkanoic acid not only enables a solvent modulated reversible interchange of ZIS between the colloidal state for efficient reaction and the aggregated state for facile separation, but also serves as a precursor for light initiated generation of reactive thiyl radical for highly selective cleavage of β-O-4 bond in native lignin. This work provides a green and efficient strategy for the depolymerization of native lignin to functionalized aromatic monomers under mild conditions, which involves a new mechanism for the cleavage of β-O-4 bonds in native lignin. The capability of cleavage of β-O-4 bonds in native lignin by photogenerated thiyl radicals also demonstrates the great potential of using photogenerated thiyl radicals in organics transformations.

A Hexaarylbiimidazole-Terarylene Hybrid: Visible-to-NIR-II Absorption via Sequential Photochromic Reactions.

A synergetic interaction between two or more photochromic chromophores has a potential to achieve advanced photochemical properties beyond conventional photochromic molecules and to realize photochemical control of complex systems using only a single molecule. Herein, we report a hybrid photochromic molecule consisting of hexaarylbiimidazole (HABI) and terarylene that exhibits multi-state photochromism. The biphotochrome hybrid shows four-state photochromic reaction involving sequentially proceeding photoreactions. The UV or visible light irradiation to the biphotochrome leads to the C-N bond breaking reaction of the HABI in preference to the ring-closing reaction of the 6π-electron system in the terarylene unit, leading to two terarylene radical molecules. The photogenerated terarylene radical further exhibits the 6π-electrocyclization reaction by UV irradiation. The delocalized π-radical on the closed-ring form of the terarylene is efficient to enhance the photosensitivity to the NIR-I and -II region. Furthermore, a recombination reaction of radicals between the open- and closed-ring isomers of terarylene affords an unprecedented photochromic dimer as a structural isomer of the initial molecule. This is a consequence of the sequential hybrid photochromic system involving the HABI and terarylene units.

Modulation of cell death mechanisms via α-Ag2WO4 morphology-dependent factors

The cytotoxic of α-Ag2WO4 synthesized in different morphologies (cuboidal (AW-C), hexagonal rod-like (AW-HRL) and nanometric rod-like (AW-NRL) was analyzed to understand the impact of morphological modulation on the toxicity of 3 T3 cell lines in the dark and when photoactivated by visible light. Pathways of toxicity were examined, such as parameters and electrostatic interaction, uptake, ion release and ROS production. Cytotoxicity was observed for all samples after reaching concentrations exceeding 7.8 μg/mL. Uptake tests demonstrated that the samples were not internalized by cells, likely due to their negative surface charge. AW-NRL exhibited autophagy in the absence of light and during photoactivation, primarily attributed to its ability to generate singlet oxygen. Analyzing intercellular ROS and RNS production, AW-HRL induced an increase in NO through exposure to photo-generated hydroxyl radicals, while AW-NRL showed increases only at non-photoactivated concentrations and AW-C did not exhibit increases. Interestingly, in the dark, these cells showed a low propensity for apoptosis, with late apoptosis and necrosis being more pronounced. When photoactivated, this behavior changed, revealing predominantly apoptotic and late apoptotic cell death. There is a need for an understanding of how morphology can alter the biological properties of α-Ag2WO4 to predict and optimize its effects on cellular responses.

Engineering a staggered type-II Bi2WO6/WO3 heterojunction with improved photocatalytic activity in wastewater treatment

In recent years, the removal organic pollutants from wastewater by advanced oxidation processes, especially photocatalysis, has become a meaningful approach due to its eco-friendliness and low cost. Herein, staggered type-II Bi2WO6/WO3 heterojunction photocatalysts were prepared by a facile hydrothermal route and investigated by modern physicochemical methods (X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption-desorption, and diffuse reflectance spectroscopy). The optimized BWOW-5 photocatalyst exhibited a H2O2-assisted photocatalytic methylene blue removal efficiency of 94.1% (k = 0.01414 min−1) within 180 min under optimal reaction conditions, which is much higher than that of unmodified Bi2WO6 and WO3 due to efficient separation of the photogenerated charge carriers. The trapping experiments demonstrated that photogenerated hydroxyl radicals and holes play a key role in the photodegradation reaction. Moreover, the optimized BWOW-5 heterojunction photocatalyst exhibited excellent activity in the H2O2-assisted degradation of other pollutants, namely phenol, isoniazid, levofloxacin, and dibenzothiophene with the removal rate of 63.1, 73.6, 95.0, and 72.4%, respectively. This investigation offers a design strategy for Bi2WO6-based multifunctional photocatalytic composites with improved activity for organic pollutant degradation.

Photocatalytic defluorination of ciprofloxacin by nitrogen-defected g-C3N4 under simulated sunlight: Mechanistic insight and pathway analysis

The photocatalytic degradation of ciprofloxacin (CIP) has been widely reported to be induced by ring cleavage and defluorination. However, the role of photo-generated reactive radicals, especially electrons, in defluorination remains controversial. This study investigates the effects of reactive radicals such as hydroxyl radicals (·OH) and electrons on CIP degradation and defluorination in photocatalytic processes by nitrogen-defected g-C3N4. Almost complete CIP degradation and 46.5 % defluorination were obtained under the best conditions tested. Scavenging tests, degradation intermediate product identification, and theoretical calculations were performed to explore the reaction routes driven by ·OH and electrons in depth. Scavenging tests revealed that ·OH and electrons were predominantly responsible for direct CIP defluorination, whereas electrons played an indirect role as critical intermediates for the formation of ·OH. Time-dependent intermediate evolution analysis demonstrated that CIP degradation mainly occurred by piperazine ring cleavage and defluorination. Density functional theory (DFT) calculations based on the Hirschfeld charge, Fukui index and electrostatic potential confirmed that zwitterionic CIP+- is more reactive than CIP+ and that the piperazine ring in CIP is susceptible to nucleophilic and radical attacks by ·O2– and ·OH. Finally, electron-assisted ·OH substitution and C-F bond cleavage were proposed as the main mechanisms for CIP defluorination. This study provides a thorough understanding of CIP defluorination mechanisms by nitrogen-defected g-C3N4-based photocatalysis.

In situ preparation of two-dimensional mortise and tenon structure g-C3N4/MoO3 photocatalyst for the reduction of aqueous Cr(VI)

In situ solid-state synthesis was employed to prepare the [Formula: see text] (CM) heterojunctions with a two-dimensional mortise and tenon structure. The prepared products were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, suggesting that amorphous graphitic carbon was obtained. The photocatalytic performance of the prepared photocatalysts was evaluated in aqueous Cr(VI) reduction reactions under visible-light ([Formula: see text] > 420 nm) irradiation. The results of the experiments showed that the photocatalytic activity of CM is influenced by the composition of heterojunctions. The optimum photocatalytic activity for the photocatalytic reduction of Cr(VI) was found in the compound CM-25, which contains a 25% [Formula: see text] concentration. The Cr(VI) reduction rate on CM-25 was four times that of [Formula: see text] and 14.5 times that of [Formula: see text], the photocatalytic activity of CM-25 only dropped by 7.7% in four cycles. Scavenger investigations and EPR tests indicated that the major photogenerated radicals in the reduction of Cr(VI) were superoxide negative radicals (•[Formula: see text]) and hydroxyl radicals (•[Formula: see text]OH). CM-25 was discovered to be an S-scheme heterojunction that effectively suppressed photogenerated charge carrier recombination and retained photogenerated holes (in the valence band of [Formula: see text]) and electrons (in the conduction band of [Formula: see text]) with higher redox capabilities. CM-25 has potential applications in the photocatalytic reduction of Cr(VI) in wastewater.

Photosensitive polyimide enabled simple, reversible and environmentally friendly selective metallization on diverse substrates

For breaking through the limitation of metal patterning in constructing conductive pathways of electronic devices, which is proposed to be an upgrade of traditional etching technique, a photo-reversible, transparent and soluble polyimide carrying spiropyran side chains is synthesized. The merocyanine isomers produced from the spiropyran moieties under digitalized ultraviolet irradiation bind the silver−histidine complexes in water, while the absorbed silver ions are in-situ reduced into metal silver seeds by the photo-generated radicals from histidine molecules, catalyzing copper deposition and yielding the desired copper patterns. Accordingly, the conventional time-consuming steps (like surface modification, immobilization of catalytic ions and (photo)chemical reduction) are simplified to a single one, and the environmentally unfriendly solvent and costly/toxic palladium reagent are excluded. The Cu patterns deposited on the polyimide show high resolution, electrical conductivity (1.785 × 10−6 Ω‧cm), adhesion strength (18.14 MPa) and fatigue resistance (> 2.6 million cycles of bending). Due to the absence of invasive surface treatments (e.g., surface hydrolysis and laser direct structuring), extremely low surface roughness of 7.83 nm is achieved. Besides, the developed strategy can be easily expanded to stretchable elastomer and other organic/inorganic substrates with irregular surfaces, showing promising application prospects. The solubility of the polyimide and ultraviolet/visible light triggered reversibility of the included spiropyran groups further enable repeated recycling, erasing and re-patterning.

Photochromism and Photomagnetism in Two Ni(II) Complexes Based on a Photoactive 2,4,6-Tris-2-Pyridyl-1,3,5-Triazine Ligand.

It is still challenging to construct novel photochromic and photomagnetic materials in the field of molecular materials. Herein, the 2,4,6-tris-2-pyridyl-1,3,5-triazine (TPTz) molecule was found to display photochromic properties under room temperature light irradiation. Two mononuclear structures, [Ni(H2O)(TPTz)(C2O4)]·2H2O (1; C2O42- = oxalate) [Ni(H2O)(TPTz)(C2O4)]·0.5H2O (2), and one chain compound [Ni(TPTz)(H2-HEDP)]·2H2O (3; HEDP = hydroxyethylidene diphosphonate) were obtained by assembling TPTz with polydentate O-ligands (oxalate and phosphonate) and the paramagnetic Ni2+ ions. The electron-transfer (ET)-dominated photochromism was observable in 1 and 2 after light irradiation with the photogeneration of relatively stable radicals, and the resultant photochromism was demonstrated via UV-vis, photoluminescence, X-ray photoelectron spectra, electron paramagnetic resonance spectra, and molecular orbital calculations. Due to the denser stacking interactions between the adjacent organic molecules, 2 exhibited a faster photochromic rate than 1. Compared with 1 and 2, compound 3 did not show photochromic behavior, which was deciphered by the theoretical calculations for all of the compounds. Importantly, the magnetic couplings appeared between photogenerated radicals and paramagnetic Ni2+ ions, resulting in a scarcely photomagnetic phenomenon of 1 and 2 in the Ni-based electron transfer photochromic materials. This work enriches the available kind of ligands for the design of ET photochromic materials, putting forward a method to tune the electron transfer photochromic efficiency in the molecular materials.