Transient Fluorescence Research Articles

Enhanced luminescence of a new red phosphor Na13Sr2Ta2(PO4)9:Eu3+ by co-doping charge compensators Li+/Na+/K+

A new type of red emitting phosphor Eu3+-doped Na13Sr2Ta2(PO4)9 (NSTP) was synthesized by high temperature solid-state method. The effects of Eu3+ doping concentration on crystal structure and optical properties were studied by powder X-ray diffraction (XRD), steady state and transient state fluorescence spectroscopy. NSTP:Eu3+ phosphors glowed red light when stimulated by near-ultraviolet light of 394 nm, due to the 4f→4f transitions of Eu3+. The optimal Eu3+ doping concentration in NSTP host matrix was determined to be x = 0.2, excess dopant will lead to concentration quenching due to the dipole-dipole interaction. At 420 K, the relative luminous intensity remains about 76% of the initial intensity at 300 K, which shows that NSTP:0.2Eu3+ phosphor has good thermal stability. Furthermore, three alkali metal ions, Li+, Na+ and K+ were introduced as charge compensators to improve luminescent efficiency. In comparison, all three compensators can enhance the luminescence intensity, in which the self-compensating ion Na+ is the best one. The internal quantum yield (IQY) of phosphor NSTP:0.2Eu3+,0.2Na+ was measured to be 44.94%, suggesting its potential application in LEDs as a red component.

Redox‐Mediated Transient Reconfiguration of a Supramolecular Assembly

AbstractDissipative systems, that constantly consume energy for sustenance, are ubiquitous and essential to life. In synthetic systems, the phenomenon promises emergent properties and different structure from the ones existing at thermodynamic equilibrium. It can create reconfigurable and temporally programmable life‐like smart materials. In this study, we attempt to create reconfigurable, temporally programmable self‐assembly using the redox chemistry of a core‐substituted naphthalene diimide derivative. As a result, transient reconfiguration of supramolecular assembly from vesicle to sheet along with transient fluorescence switching with fuel‐dependent lifetime is attained. We believe that such a design strategy can advance the synthesis of active, adaptive and autonomous materials.

Singlet Fission in Tetraaza-TIPS-Pentacene Oligomers: From fs Excitation to μs Triplet Decay via the Biexcitonic State

Generating two long-living low-energy excitations after absorption of a single high-energy photon has stoked interest in singlet fission (SF) to enhance solar energy conversion in photovoltaics. To this end, survival of the triplet states is critical. This process is investigated in diethynylbenzene-linked tetraaza-triisopropylsilylethynyl-pentacene dimers, for which SF is energetically feasible and facilitated by the close distances between the azapentacenes. The ortho and meta connectivities are explored and compared with the tetraazapentacene molecule and the (1,3,5) trimer. Efficient SF (potential ΦT ≥ 160%) is demonstrated in all oligomers by quantitative kinetic analysis of broadband transient absorption and fluorescence signals. Together with dynamics of the starting singlet, the triplet pair, and the final free triplet state, our results show an intermediate component with spectral properties compatible with a biexcitonic state. Long-living triplets represent only a fraction of the high number of transient triplet pair intermediates, which undergo triplet-triplet annihilation as well as fusion between neighboring pentacenes. Therefore, our work provides new insight into the SF in covalent dimers and paves the way for the application of these materials for carrier multiplication.

Limited Diclosulam Herbicide Uptake and Translocation-Induced Tolerance in Crotalaria juncea.

The study was to identify the potential tolerance of Crotalaria juncea to diclosulam uptake and translocation and its effects on the physiological metabolism of plants. Two experiments were carried out; I-Evaluation of uptake and translocation of 14C-diclosulam (35g a.i. ha-1) in C. juncea, at seven and 14days after emergence. II-Evaluation of chlorophyll a transient fluorescence of dark-adapted C. juncea leaves when applied diclosulam in pre-emergence. Plants of C. juncea presented an anatomical/metabolic barrier to diclosulam translocation in the stem, which may confer tolerance to this herbicidal, besides reduced translocation due to low accumulation in the cotyledons. In addition, plants can maintain photosynthetic metabolism active when growing in soil with diclosulam by not changing the dynamics of energy dissipation. Thus, when cultivated in soil with residual of diclosulam, C. juncea can tolerate the herbicide to maintain plant growth.

Theory of fluorescence spectrum dynamics and its application to determining the relaxation characteristics of the solvent and intramolecular vibrations

A general analytical expression for the transient fluorescence spectrum is derived. The formation of a wave packet in the excited state of a fluorophore is described, assuming that the pump pulse has a Gaussian time-profile. The expression explicitly connects the relaxation characteristics of the medium with the spectral dynamics of a fluorophore. Fitting the expression to experimental spectral dynamics allows obtaining the solvent relaxation function. So far this approach was applicable for the analysis of experimental data when the pump pulse does not populate excited sublevels of intramolecular high-frequency vibrational modes. Here, the approach is generalized to include vibrational relaxation in the excited electronic state. In this case, fitting to the experimental spectral dynamics provides reliable information not only on the solvent relaxation, but also on the relaxation time constants of intramolecular high-frequency vibrational modes. This approach is applied to the excited state dynamics of coumarin 153 in multiple solvents, obtained from broadband fluorescence upconversion spectroscopy.

Interactions between tetracycline and extracellular polymeric substances in anammox granular sludge

The effects of antibiotics on extracellular polymeric substances (EPS) using tetracycline as the model chemical were analyzed in terms of molecular property and structure. Results showed that three components, tryptophan, tryptophan type-proteins and polysaccharides in EPS of granular sludge from anaerobic ammonium oxidation (anammox) reactor can interacted with tetracycline, detected by the static quenching via the endogenous fluorescence quenching and transient fluorescence spectroscopy. Thermodynamic experiment confirmed that their interaction was dominated by the hydrophobic force. Combined with the synchronous fluorescence spectroscopy, it was found that tetracycline facilitated the extension degree of peptide chains in tryptophan type-proteins, leading to the enhancement of hydrodynamic diameter of the macromolecules in EPS when binding with tetracycline. EPS in AnGS demonstrated the resistance ability to tetracycline by converting from gel to sol state in rheological term. With the increase of tetracycline concentration, the stability of elastic structures in EPS declined, influencing the AnGS stability.

Characterization of the transient fluorescence wave phenomenon that occurs during H2 production in Chlamydomonas reinhardtii.

The redox state of the plastoquinone (PQ) pool in sulfur-deprived, H2-producing Chlamydomonas reinhardtii cells was studied using single flash-induced variable fluorescence decay kinetics. During H2 production, the fluorescence decay kinetics exhibited an unusual post-illumination rise of variable fluorescence, giving a wave-like appearance. The wave showed the transient fluorescence minimum at ~60 ms after the flash, followed by a rise, reaching the transient fluorescence maximum at ~1 s after the flash, before decaying back to the initial fluorescence level. Similar wave-like fluorescence decay kinetics have been reported previously in anaerobically incubated cyanobacteria but not in green algae. From several different electron and proton transfer inhibitors used, polymyxin B, an inhibitor of type II NAD(P)H dehydrogenase (NDA2), had the effect of eliminating the fluorescence wave feature, indicating involvement of NDA2 in this phenomenon. This was further confirmed by the absence of the fluorescence wave in the Δnda2 mutant lacking NDA2. Additionally, Δnda2 mutants have also shown delayed and diminished H2 production (only 23% if compared with the wild type). Our results show that the fluorescence wave phenomenon in C. reinhardtii is observed under highly reducing conditions and is induced by the NDA2-mediated electron flow from the reduced stromal components to the PQ pool. Therefore, the fluorescence wave phenomenon is a sensitive probe for the complex network of redox reactions at the PQ pool level in the thylakoid membrane. It could be used in further characterization and improvement of the electron transfer pathways leading to H2 production in C. reinhardtii.

Exploring the effects of boron nitride coating on the thermal stability and photoluminescence properties of molybdenum disulfide nanospheres

Here, we sprang up a novel approach to synthesize molybdenum disulfide nanoparticles coated by hexagonal boron nitride via high-temperature sintering technique under floating ammonia gas at 900 °C for 3 h MoS2-BN nanocomposites have significant thermal stability with an oxidation temperature of 715 °C, indicating that its antioxidant performance increased by 217% compared with the pure MoS2 nanospheres. Additionally, the strong red PL signal of MoS2-BN characterized by Steady state transient fluorescence spectrometer appears at ~678 nm at room temperature, its strength has reached 3.14 × 106 CPS, while the original MoS2 nanospheres shows almost no characteristics, demonstrating that the nanocomposites have excellent luminescent properties. Therefore, the improved properties of molybdenum disulfide materials encapsulated by hexagonal boron nitride (h-BN) expand the applications of MoS2 nanospheres in high temperature and optoelectronic devices, which could pave way for the h-BN encapsulated transition metal dichalcogenides (TMDCs).

Basic properties and photo-generated carrier dynamics of bismuth vanadate composites modified with CQDs, MWCNTs and rGO

Three types of carbon materials with different dimensions were successfully combined with bismuth vanadate (BiVO4) using different methods, resulting in BiVO4/carbon quantum dots (CQDs), BiVO4/hydroxylated multiwalled carbon nanotubes (MWCNTs) and BiVO4/reduced graphene oxide (rGO). First, analysis of the basic morphology and elemental characterization of the materials were performed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectroscopy (UV–vis DRS). Second, the effects of conductivity on the separation and recombination efficiency of the photo-generated carriers were investigated using photoluminescence spectroscopy (PL), transient fluorescence, electron spin resonance (ESR), transient photocurrent density (TPD) and electrochemical impedance spectroscopy (EIS). These results showed the addition of carbon promoted the separation of photo-generated carriers. Transient fluorescence measurements showed the separation and recombination of carriers was an ultrafast kinetic process and the photo-generated carriers exhibited the following three recombination mechanisms during fluorescence decay: bulk recombination, surface migration and defect recombination. In this study, photocatalytic carrier separation was improved by the addition of carbon materials, which resulted in improved photocatalytic degradation. Examination of the kinetic process of carbon-modified BiVO4 composites resulted in a deeper understanding of the composite process of the photo-generated carriers and the development of a better research method for improving photocatalytic degradation effects.

Exploring the influence of silver nanoparticles on the mechanism of fluorescence quenching of coumarin dye using FRET

A study has been undertaken on fluorescence resonance energy transfer (FRET) between microwave assisted silver nanoparticles (AgNPs) and biologically active coumarin derivative 2-acetyl-3H-benzo[f]chromen-3-one (2AHBC). The Stern-Volmer plot shows linear nature in steady state and transient state fluorescence quenching. By employing FRET theory, different parameters such as number of binding sites, energy transfer rate, binding distance, association constant and energy efficiency have been determined for fluorescent probe 2AHBC in propanol solvent with AgNPs at room temperature.

RGO Boosts Band Gap Regulates for Constructing Ni2P/RGO/MoO2 Z-Scheme Heterojunction to Achieve High Efficiency Photocatalytic H2 Evolution

A Z-scheme heterojunction composite material Ni2P/RGO/MoO2 with high efficiency HER activity via a simple hydrothermal synthesis method which is one-step for photocatalytic H2 production was synthesized. The composite material which used reduced graphene oxide (RGO) as an electron transport medium and utilized a synergistic action of non-noble metal semiconductors Ni2P and MoO2 to construct Z-scheme heterojunction. Compared with the binary Ni2P/MoO2 composite photocatalyst, the photocatalytic hydrogen evolution activity of RGO assisted ternary composite Ni2P/RGO/MoO2 is significantly improved under visible light (λ > 420 nm) in the dye sensitization system in 5 h. The photocatalyst with optimal ratio reaches 355.34 μmol, which is about two times as much as the one without RGO. The transient photocurrent response, fluorescence test and hydroxyl radical capture experiment show that the type-II heterojunction originally composed of Ni2P and MoO2 is converted to Z-scheme in the presence of RGO. The transformation of the electron transfer mode effectively reduces the composite of photogenerated carriers. In addition, in situ hydrothermal synthesis allows Ni2P and MoO2 to be firmly modified on the RGO surface. This makes the composite photocatalyst exhibit great catalytic stability, and the HER activity of the photocatalyst hardly decrease in the four-cycle experiment. Through the one-step hydrothermal method, RGO assisted non-precious metal semiconductor composite provides a new idea for the synthesis of photocatalytic materials. The composite catalyst via the band gap regulation of MoO2 by Ni2P exhibits great hydrogen production activity in the dye-sensitized system. Subsequently, the GO solution was added during the synthesis to construct a Z-scheme heterojunction with graphene as an electron transporter. The ternary composite catalyst with a Z-scheme heterojunction shows approximately twice the hydrogen production rate of the binary catalyst.

Calcium carbonate particle films and water regimes affect the acclimatization, ecophysiology and reproduction of tomato

Tomato is one of the world´s more important vegetables and demands a high consumption of water in production. Climate conditions with high levels of temperatures, solar radiation, and water restriction events affect plant physiology, reproduction, and fruit quality. Particle films (PF) of kaolin have been demonstrated to be an alternative and efficient technology to promote tomato protection. However, researches with PF from calcium materials are scarce, and when considering the physiological needs of calcium throughout the crop cycle, can be strategic. The objectives of this study were to identify the isolated effects of artificial shading using different concentrations of calcium carbonate particle films on the acclimatization, ecophysiological, and reproductive parameters of tomato plants associated with two water regimes. The treatments used were calcium carbonate films (CaCO3) at concentrations of 5%, 10% and 15% (w/v) and without film or 0% (control), and two irrigation water regimes based on crop evapotranspiration (ETc), restoring 100% of ETc (WW) or 50% of ETc (WS) to simulated water stress. The research was into two experiments: the first allowed evaluating acclimatization effects by artificial shading with PF on Falker chlorophyll indices and canopying temperature in three successive applications. The second involved the combination of water regimes and PF concentrations and evaluated gas exchange, chlorophyll transient fluorescence, and flowering/fructification parameters. The results suggest that PF were able to provide acclimatization to tomato plants by artificial shading evidencing significant increases of chlorophylls and reduction in the chlorophyll a/b ratio. The associated effects of PF and water regimes indicated that PF produced a significant antitranspirant and photoprotective effect, mainly under WS, also providing physiological regulation of tomato plants during flowering/fruiting, 10% of CaCO3 accumulated better results in this sense. Particle films of CaCO3 promised to be an additional protection tool in tomato cultivation.

Xeno Nucleic Acid Nanosensors for Enhanced Stability

The omnipresence of salts in biofluids creates a pervasive challenge in designing sensors suitable for in vivo applications. Fluctuations in ion concentrations have been shown to affect the sensitivity and selectivity of optical sensors based on single-walled carbon nanotubes wrapped with single-stranded DNA (ssDNA-SWCNTs). We herein observe fluorescence wavelength shifting for ssDNA-SWCNT-based optical sensors in the presence of divalent cations at concentrations above 3.5 mM. In contrast, no shifting was observed for concentrations up to 350 mM for sensors bioengineered with increased rigidity using xeno nucleic acids (XNAs). Transient fluorescence measurements reveal distinct optical transitions for ssDNA- and XNA-based wrappings during ion-induced conformation changes, with XNA-based sensors showing increased permanence in conformational and signal stability. This demonstration introduces synthetic biology as a complementary means for enhancing nanotube optoelectronic behaviour, unlocking previously unexplored possibilities for developing nano-bioengineered sensors with augmented capabilities.

A study on film formation and fluorescence enhancement of PS latex/AgNPs composites depending on AgNPs content and annealing

In the work reported here, we investigated the characteristic change in film formation, optical, morphological and electrical properties of pyrene (P) labeled polystyrene (PS) latex/silver nanoparticles (AgNPs) (PS/AgNPs) composites by using steady state (SSF) and fast transient (FTRF) fluorescence techniques in conjunction with UV–VIS (UVV) technique. Nine different mixtures were prepared by mixing of PS latex dispersion with different amount of AgNPs in the range of 0–50 wt%. PS/AgNPs films were then prepared on glass substrates using drop casting method and drying at room temperature. After drying, film samples were separately annealed above the glass transition temperature (Tg) of PS ranging from 100 to 280 °C. Fluorescence emission spectrum, fluorescence decay curve and transmittance of these composites were measured after each annealing step as a function of AgNPs content. The emission spectrum became narrower with increasing AgNPs content due to interactions between the pyrenes and the electron plasma in nearby silver nanoparticles. Fluorescence enhancement and reduced lifetime were also observed with increasing AgNPs content in the range of 3–20 wt%. Almost a 4 fold increase in emission intensity of pyrene were observed for 10 wt% of AgNPs content film. In order to monitor the film formation process, fluorescence intensities (IP) from P and transmitted light intensity (Itr) through the films were measured after each annealing step. Below 40 wt% of AgNPs, two distinct film formation stages, which are named as void closure and interdiffusion processes, were seen in fluorescence data. However, above 40 wt%, no change was observed in IP upon annealing, whereas transparency decreased overall with increasing AgNPs content. The electrical conductivity of these composites showed very little increase with increasing AgNPs. Film morphologies were also found as consistent with optical data.

Highly efficient full color light-emitting diodes based on quantum dots surface passivation engineering

High-efficiency quantum dots light-emitting diodes have been showing promise in the development of optoelectronic devices in displays and solid-state lighting. However, quantum dots surface traps strongly quench its luminescence when transfer it from in solution into on film. We propose a reproducible method of studying photoluminescence decay dynamics in nanocrystals by implementing surface passivation engineering, the results reveal that quantum dots surface traps-being the main cause of the fluorescence quenching and non-radiative recombination-could be eliminated by a series of surface post-treatment processes. Moreover, we study the quantum dots transient fluorescence spectra that the PL decay channel turned from the double exponential decay (control) to the mono-exponential decay kinetics (both the green and red quantum dots with UV-water co-treatment), and their quantum yields and stability are improved. Here we report all solution-processed multilayer monochromatic quantum dots light-emitting diodes what the emitting layer is formed from the surface post-treated red/green/blue quantum dots. These devices have exhibited a maximum current efficiency and external quantum efficiencies (EQE) of 20.7 cd/A and 14.4% for red, 65.1 cd/A and 15.9% for green, and 4.8 cd/A and 14.7% for blue devices, respectively. We expect the successful quantum dots surface passivation engineering would exert profound influence on their applications to light emitting devices.

Nuclear Receptor Corepressor 1 Regulates Thyroid Hormone Receptor Nuclear Retention

The thyroid hormone receptor (TR) mediates gene transcription in response to thyroid hormone (T3) and significantly affects cell growth, development and metabolism. Although TR shuttles rapidly between the nucleus and cytoplasm, it is primarily nuclear localized at steady state. A shift in the balance between export and import leading to TR mislocalization may correlate with certain cancers or endocrine disorders. Previously, we have identified multiple nuclear localization signals and nuclear export signal within TR that interact with importins and exportins, respectively, to mediate shuttling. Given that TR contains multiple, competing import and export signals, the question arises: what factors are involved in nuclear retention of TR? In addition to DNA‐binding sites, the lab's prior research indicated that nuclear coactivator MED1 facilitates TR nuclear localization. Thus, we hypothesize that certain transcriptional coregulators, including Nuclear Receptor Corepressor 1 (NCoR1), contribute to TR nuclear retention. Using transient transfection assays and fluorescence microscopy, we measured the fluorescent intensity of GFP or mCherry‐tagged TR in the nucleus (N) and cytoplasm (C) of HeLa cells, and then calculated the N/C ratio as an indicator of intracellular localization patterns. We discovered that when NCoR1 is knocked down by shRNA, the amount of TR in the nucleus decreased significantly (lower N/C ratio). Inversely, when NCoR1 is over‐expressed, the amount of TR in the nucleus significantly increased (higher N/C ratio). An even more dramatic cytosolic shift was observed for a TR mutant that cannot bind to NCoR1 (AHT‐TR). Taken together, our results suggest that NCoR1 is a key regulator of TR nuclear retention. This finding will contribute to the development of a dynamic mathematical model that aims to predict TR's N/C ratio during the interaction with different complexes and TR localization's effect on transcriptional output of T3‐dependent genes.Support or Funding InformationNIH 2R15DK058028This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Carbon Nanodots for Charge-Transfer Processes.

In recent years, carbon nanodots (CNDs) have emerged as an environmentally friendly, biocompatible, and inexpensive class of material, whose features sparked interest for a wide range of applications. Most notable is their photoactivity, as exemplified by their strong luminescence. Consequently, CNDs are currently being investigated as active components in photocatalysis, sensing, and optoelectronics. Charge-transfer interactions are common to all these areas. It is therefore essential to be able to fine-tune both the electronic structure of CNDs and the electronic communication in CND-based functional materials. The complex, but not completely deciphered, structure of CNDs necessitates, however, a multifaceted strategy to investigate their fundamental electronic structure and to establish structure-property relationships. Such investigations require a combination of spectroscopic methods, such as ultrafast transient absorption and fluorescence up-conversion techniques, electrochemistry, and modeling of CNDs, both in the absence and presence of other photoactive materials. Only a sound understanding of the dynamics of charge transfer, charge shift, charge transport, etc., with and without light makes much-needed improvements in, for example, photocatalytic processes, in which CNDs are used as either photosensitizers or catalytic centers, possible. This Account addresses the structural, photophysical, and electrochemical properties of CNDs, in general, and the charge-transfer chemistry of CNDs, in particular. Pressure-synthesized CNDs (pCNDs), for which citric acid and urea are used as inexpensive and biobased precursor materials, lie at the center of attention. A simple microwave-assisted thermolytic reaction, performed in sealed vessels, yields pCNDs with a fairly homogeneous size distribution of ∼1-2 nm. The narrow and excitation-independent photoluminescence of pCNDs contrasts with that seen in CNDs synthesized by other techniques, making pCNDs optimal for in-depth physicochemical analyses. The atomistic and electronic structures of CNDs were also analyzed by quantum chemical modeling approaches that led to a range of possible structures, ranging from heavily functionalized, graphene-like structures to disordered amorphous particles containing small sp2 domains. Both the electron-accepting and -donating performances of CNDs make the charge-transfer chemistry of CNDs rather versatile. Both covalent and noncovalent synthetic approaches have been explored, resulting in architectures of various sizes. CNDs, for example, have been combined with molecular materials ranging from electron-donating porphyrins and extended tetrathiafulvalenes to electron-accepting perylendiimides, or nanocarbon materials such as polymer-wrapped single-walled carbon nanotubes. In every case, charge-separated states formed as part of the reaction cascades initiated by photoexcitation. Charge-transfer assemblies including CNDs have also played a role in technological applications: for example, a proof-of-concept dye-sensitized solar cell was designed and tested, in which CNDs were adsorbed on the surface of mesoporous anatase TiO2. The wide range of reported electron-donor-acceptor systems documents the versatility of CNDs as molecular building blocks, whose electronic properties are tunable for the needs of emerging technologies.

Coupled Excited-State Dynamics in N-Substituted 2-Methoxy-9-Acridones.

Fluorophores of the acridone family have been widely employed in many applications, such as DNA sequencing, the detection of biomolecules, and the monitoring of enzymatic systems, as well as being the bases of intracellular sensors and even antitumoral agents. They have been widely used in fluorescence imaging due to their excellent photophysical properties, in terms of quantum yield and stability. However, frequently, the fluorescence emission data from acridones are not easily interpretable due to complex excited-state dynamics. The formation of π-stacking aggregates and excimers and excited-state proton transfer (ESPT) reactions usually result in emission features that are dependent on the experimental conditions. Therefore, an in-depth understanding of the dynamics involved in the excited-state transients of these dyes is mandatory for their appropriate application. Herein, we synthesized and fully characterized different 2-methoxy-9-acridone dyes. Their transient fluorescence emission spectra exhibited a complex dynamic behavior that can be linked to several excited-state reactions. We performed a thorough study of the excited-state dynamics of these dyes by means of time-resolved fluorimetry supported by computational calculations. All this allowed us to establish a multistate kinetic scheme, involving an ESPT reaction coupled to an excimer formation process. We have unraveled the rich dynamics behind this complex behavior, which provides a better understanding of the excited states of these dyes.

Controllable design of Zn-Ni-P on g-C3N4 for efficient photocatalytic hydrogen production

Synthesizing a stable and efficient photocatalyst has been the most important research goal up to now. Owing to the dominant performance of g-C3N4 (graphitized carbonitride), an ordered assemble of a composite photocatalyst, Zn-Ni-P@g-C3N4, was successfully designed and controllably prepared for highly efficient photocatalytic H2 evolution. The electron transport routes were successfully adjusted and the H2 evolution was greatly improved. The maximum amount of H2 evolved reached about 531.2 μmol for 5 h over Zn-Ni-P@g-C3N4 photocatalyst with a molar ratio of Zn to Ni of 1:3 under illumination of 5 W LED white light (wavelength 420 nm). The H2 evolution rate was 54.7 times higher than that over pure g-C3N4. Moreover, no obvious reduction in the photocatalytic activity was observed even after 4 cycles of H2 production for 5 h. This synergistically increased effect was confirmed through the results of characterizations such as XRD, TEM, SEM, XPS, N2 adsorption, UV-vis DRS, transient photocurrent, FT-IR, transient fluorescence, and Mott-Schottky studies. These studies showed that the Zn-Ni-P nanoparticles modified on g-C3N4 provide more active sites and improve the efficiency of photogenerated charge separation. In addition, the possible mechanism of photocatalytic H2 production is proposed.

Intramolecular Reductive Cyclization of o-Nitroarenes via Biradical Recombination.

A visible-light-induced/thiourea-mediated intramolecular cyclization of o-nitroarenes under mild conditions is realized for the first time, which provides an efficient and environmentally friendly way to access pharmaceutical relevant quinazolinone derivatives. The reaction can be easily extended to gram level by using a continuous-flow setup with high efficiency. Mechanistic investigation including control experiments, transient fluorescence, UV-vis spectra, and DFT calculations suggests that the formation of active biradical intermediates via intramolecular single electron transfer (SET) is key stage in the catalytic cycle.