Showing papers in "ChemPlusChem in 2018"
TL;DR: A Review of theoretical studies in singlet fission since 2006, the year when the research interest in this subject was reignited is presented, both electronic structure and dynamics studies are covered.
Abstract: In this Review article, a survey is given for theoretical studies in the subject of singlet fission. Singlet fission converts one singlet exciton to two triplet excitons. With the doubled number of excitons and the longer lifetime of the triplets, singlet fission provides an avenue to improve the photoelectric conversion efficiency in organic photovoltaic devices. It has been a subject of intense research in the past decade. Theoretical studies play an essential role in understanding singlet fission. This article presents a Review of theoretical studies in singlet fission since 2006, the year when the research interest in this subject was reignited. Both electronic structure and dynamics studies are covered. Electronic structure studies provide guidelines for designing singlet fission chromophores and insights into the couplings between single- and multi-excitonic states. The latter provides fundamental knowledge for engineering interchromophore conformations to enhance the fission efficiency. Dynamics studies reveal the importance of vibronic couplings in singlet fission.
82 citations
TL;DR: The most up-to-date design rationales and discussions providing a strong understanding of structure-property-function relationships in BODIPY-based semiconductors are presented and are expected to inspire new research for future materials developments/applications in this family of molecules.
Abstract: The rapid emergence of organic (opto)electronics as a promising alternative to conventional (opto)electronics has been achieved through the design and development of novel π-conjugated systems. Among various semiconducting structural platforms, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) π-systems have recently attracted attention for use in organic thin-films transistors (OTFTs) and organic photovoltaics (OPVs). This Review article provides an overview of the developments in the past 10 years on the structural design and synthesis of BODIPY-based organic semiconductors and their application in OTFT/OPV devices. The findings summarized and discussed here include the most recent breakthroughs in BODIPYs with record-high charge carrier mobilities and power conversion efficiencies (PCEs). The most up-to-date design rationales and discussions providing a strong understanding of structure-property-function relationships in BODIPY-based semiconductors are presented. Thus, this review is expected to inspire new research for future materials developments/applications in this family of molecules.
70 citations
TL;DR: A key lesson of this survey is that boron nitride may turn out to be a promising material for hydrogen storage at room conditions provided all the predictions come true.
Abstract: Boron nitride, BN, for hydrogen storage emerged in the beginning of the millennium and there swiftly followed more than 15 years of efforts combining experimental laboratory works and to a greater extent computational predictions. BN has been considered mainly for the storage of molecular hydrogen, H-2, by physisorption and/or chemisorption over a wide range of temperatures, that is, between -196 degrees C and 300 degrees C. Yet its potential has gone beyond the sorption of H-2 as it has been also, although less extensively, involved in chemical H storage. The present review aims at giving a comprehensive overview of the main experimental results and findings as well as of the different avenues worth being explored. A key lesson of this survey is that boron nitride may turn out to be a promising material for hydrogen storage at room conditions provided all the predictions come true. The "ball" is now in the lab experimenters' court.
46 citations
TL;DR: Time-dependent (TD)-DFT calculations show that the energy gap between the lowest-energy singlet and triplet excited states (0.12-0.20 eV) permits TADF.
Abstract: Herein, [Cu(P^P)(N^N)][PF6 ] complexes (P^P=bis[2-(diphenylphosphino)phenyl]ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos); N^N=CF3 -substituted 2,2'-bipyridines (6,6'-(CF3 )2 bpy, 6-CF3 bpy, 5,5'-(CF3 )2 bpy, 4,4'-(CF3 )2 bpy, 6,6'-Me2 -4,4'-(CF3 )2 bpy)) are reported. The effects of CF3 substitution on their structure as well as their electrochemical and photophysical properties are also presented. The HOMO-LUMO gap was tuned by the N^N ligand; the largest redshift in the metal-to-ligand charge transfer (MLCT) band was for [Cu(P^P){5,5'-(CF3 )2 bpy}][PF6 ]. In solution, the compounds are weak yellow to red emitters. The emission properties depend on the substitution pattern, but this cannot be explained by simple electronic arguments. Among powders, [Cu(xantphos){4,4'-(CF3 )2 bpy}][PF6 ] has the highest photoluminescence quantum yield (PLQY; 50.3 %) with an emission lifetime of 12 μs. Compared to 298 K solution behavior, excited-state lifetimes became longer in frozen Me-THF (77 K; THF=tetrahydrofuran), thus indicating thermally activated delayed fluorescence (TADF). Time-dependent (TD)-DFT calculations show that the energy gap between the lowest-energy singlet and triplet excited states (0.12-0.20 eV) permits TADF. Light-emitting electrochemical cells (LECs) with [Cu(POP)+(6-CF3 bpy)][PF6 ], [Cu(xantphos)(6-CF3 bpy)][PF6 ], or [Cu(xantphos){6,6'-Me2 -4,4'-(CF3 )2 bpy}][PF6 ] emit yellow electroluminescence. The LEC with [Cu(xantphos){6,6'-Me2 -4,4'-(CF3 )2 bpy}][PF6 ] had the fastest turn-on time (8 min), and the LEC with the longest lifetime (t1/2 =31 h) contained [Cu(xantphos)(6-CF3 bpy)][PF6 ]; these LECs reached maximum luminances of 131 and 109 cd m-2 , respectively.
43 citations
TL;DR: The results show that the charging/discharging electric capacity of the fabricated λ-MnO2 film electrode was up to up to ≈100 mAh g-1 at a current density of 50 mA G-1 in 30 mm Li+ aqueous solution, twice that of the λ.O2 powder electrode, indicating high availability and good stability of the €2 spinel on the electrode.
Abstract: Lithium recovery from an aqueous resource was accelerated by electrochemically driving the transformation of MnIV /MnIII with a spinel λ-MnO2 film electrode. A λ-MnO2 electrode without binders or conductive additives is preferred for achieving a large capacity at high current density and long-term cycling capability. In this study, a film of Mn(OH)2 was first deposited on the surface of Pt or graphite substrates owing to alkalization near the cathode, then it was oxidized to a Mn3 O4 film by air, followed by being hydrothermally lithiated to LiMn2 O4 spinel and, finally, it was turned into the λ-MnO2 film electrode through potentiostatic delithiation. The results show that the charging/discharging electric capacity of the fabricated λ-MnO2 film electrode was up to ≈100 mAh g-1 at a current density of 50 mA g-1 in 30 mm Li+ aqueous solution, twice that of the λ-MnO2 powder electrode. Also, 82.3 % lithium capacity remained after 100 cycles of an electrochemically assisted lithium recovery process, indicating high availability and good stability of the λ-MnO2 spinel on the electrode. The energy consumption for each cycle is estimated to be approximately 1.55±0.09 J, implying that only 4.14 Wh is required for recovery of one mole of lithium ions by this method.
37 citations
TL;DR: Investigating a diverse range of MOFs to rationalise how the different building blocks that form the structure can affect the electronic properties and dielectric response confirms that the band gap is primarily due to the electronic levels of the organic linkers and that tuning theBand gap can be easily achieved either by linker functionalisation or by increasing the aromaticity.
Abstract: Metal-organic framework (MOF) materials have recently been shown to have promising electronic and dielectric properties. This study involves investigating a diverse range of MOFs to rationalise how the different building blocks that form the structure can affect the electronic properties and dielectric response. The analysis, based on quantum mechanical calculations, includes the contribution from the metals involved, the organic linkers and the symmetry and topology of the framework and makes suggestions for future work on low-κ dielectric MOFs. The results confirm that the band gap is primarily due to the electronic levels of the organic linkers and that tuning the band gap can be easily achieved either by linker functionalisation or by increasing the aromaticity. The relevance of simple structure-property relationships for different families of isoreticular MOFs through the use of Hammett sigma constants is also highlighted. It is also shown that the polarisability of the framework can be tuned comparably to the band gap. However, the expected low static dielectric constant is less influenced by the composition of the MOF and can be modified by acting on the crystal structure. Indeed, it is shown that it can be directly linked to the framework porosity.
34 citations
TL;DR: This Minireview provides an overview of the three categories of recent advances in optical techniques for LECs, which have been shown to achieve better device properties without using new materials.
Abstract: The concept of solid-state light-emitting electrochemical cells (LECs), proposed in 1995, opened a new field in display and lighting technologies. The key advantage of this technology derives from a single emissive layer containing an emissive material and an ionic salt. Mobile ions in the emissive layer induce electrochemical doping at electrodes and thus the operation voltage can be reduced even if using air-stable electrodes. Since the first demonstration of LECs, many materials-oriented efforts have been made in improving device performance of LECs. However, some difficulties arising from material properties limit further optimizing the device characteristics of LECs. Recently, optical techniques have been shown to achieve better device properties without using new materials. Light extraction techniques recycle the light trapped in layered device structure and thus enhance the light output and efficiency of LECs. Recombination zone probing techniques offer direct evidence of carrier balance in LECs and is helpful in optimizing device performance. Spectral filtering based on microcavity effects and localized surface plasmon resonance from metal nanoparticles have the advantages of easy fabrication and compatibility with device processing of LECs. This Minireview provides an overview of the three categories of recent advances in optical techniques for LECs.
32 citations
TL;DR: Ultrafast transient absorption spectroscopy is used to demonstrate that singlet fission in perylene diimides can occur on a sub-picosecond timescale with quantum yields approaching the theoretical limit of 200 %.
Abstract: Perylene diimides are conjugated chromophores that are of considerable interest owing to their ability to transform a singlet excited state into two triplets by singlet fission. Although singlet fission has previously been reported for certain perylene diimide derivatives, there is some uncertainty about the rates and yield of the process in these materials. In this report, ultrafast transient absorption spectroscopy is used to demonstrate that singlet fission in perylene diimides can occur on a sub-picosecond timescale with quantum yields approaching the theoretical limit of 200 %.
30 citations
TL;DR: Three isomeric dinitropyrazoles (DNPs) were synthesized starting from readily available 1H-pyrazole by slightly improved methods than described in the literature and support the energetic character of the title compounds.
Abstract: Three isomeric dinitropyrazoles (DNPs) were synthesized starting from readily available 1H-pyrazole by slightly improved methods than described in the literature. 3,4-Dinitropyrazole (3), 1,3-dinitropyrazole (4), and 3,5-dinitropyrazole (5) were obtained and compared to each other with respect to thermal stability, crystallography, sensitivity and energetic performance. Two isomers (3 and 4) show high densities (1.79 and 1.76gcm(-3)) and interesting thermal behavior as melt-castable materials (3: T-melt.=71 degrees C, T-dec.=285 degrees C;5: T-melt. = 68 degrees C, T-dec.=171 degrees C). Furthermore, eight salts (sodium, potassium, ammonium, hydrazinium, hydroxylammonium, guanidinium, aminoguanidinium and 3,6,7-triamino-[1,2,4]triazolo[4,3-b][1,2,4]triazole (TATOT) of 3 and 5 were synthesized in order to tune performance and sensitivity values. These compounds were characterized using H-1, C-13, N-14, N-15 NMR and IR spectroscopy as well as mass spectrometry, elemental analysis and thermal analysis through differential scanning calorimetry. Crystal structures of 14 compounds were obtained (3-7, 10-12 and 15-20) by low-temperature single crystal X-ray diffraction. Impact, friction and electrostatic discharge (ESD) values were also determined by standard methods. The sensitivity values range between 8.5 and 40J for impact and 240N and 360N for friction and show mainly insensitive character. The energetic performances were determined using recalculated X-ray densities, heats of formation and the EXPLO5 code and support the energetic character of the title compounds. The calculated energetic performances (V-D: 6245-8610ms(-1);p(CJ): 14.1-30.8GPa) were compared to RDX ((O2NNCH2)(3)).
28 citations
TL;DR: Robust and efficient WO3 photoanodes for water oxidation were synthesized by the scalable one-step flame synthesis of nanoparticle aerosols and direct gas-phase deposition to provide a scalable approach for the fabrication of efficient photoelectrodes based on WO2 and other metal oxides for light-driven water splitting.
Abstract: Photoelectrochemical water splitting is a promising approach for the carbon-free production of hydrogen using sunlight. Here, robust and efficient WO3 photoanodes for water oxidation were synthesized by the scalable one-step flame synthesis of nanoparticle aerosols and direct gas-phase deposition. Nanostructured WO3 films with tunable thickness and band gap and controllable porosity were fabricated by controlling the aerosol deposition time, concentration, and temperature. Optimal WO3 films demonstrate superior water oxidation performance, reaching a current density of 0.91 mA at 1.24 V vs. reversible hydrogen electrode (RHE) and an incident photon-to-current conversion efficiency (IPCE) of ca. 61 % at 360 nm in 0.1 m H2 SO4 . Notably, it is found that the excellent performance of these WO3 nanostructures arises from the high in situ restructuring temperature (ca. 1000 °C), which increases oxygen vacancies and decreases charge recombination at the WO3 /electrolyte interface. These findings provide a scalable approach for the fabrication of efficient photoelectrodes based on WO3 and other metal oxides for light-driven water splitting.
28 citations
TL;DR: Under continuous operation, both polymer-based and ionic transition-metal complex-based LECs now exhibit a luminance half-life exceeding 1000 h, improved performance was accomplished with several effective strategies aimed at optimizing the operating scheme, the material composition, and the device architecture.
Abstract: This Minireview examines the operational lifetime of light-emitting electrochemical cells (LECs). Under continuous operation, both polymer-based LECs (PLECs) and ionic transition-metal complex (iTMC)-based LECs (iTMC-LECs) now exhibit a luminance half-life exceeding 1000 h. This improved performance was accomplished with several effective strategies aimed at optimizing the operating scheme, the material composition, and the device architecture. These strategies are presented in detail with PLECs as an example. iTMC-LECs are also highlighted owing to their excellent stress stability with regards to both luminance and operating voltage. The survey of literature data points to clear trends, as well as some unexpected results in LECs stressed for an extended period. Major challenges still exist, but long-lasting LECs are possible when the proven strategies are combined with innovative materials and device design.
TL;DR: Two different approaches to improve the quantum yields and response times of switches driven by E/Z photoisomerization or photoinduced H-atom/proton transfer reactions through simple ESA considerations are described.
Abstract: Central to the development of optoelectronic devices is the availability of efficient synthetic molecular photoswitches, the design of which is an arena where the evolving concept of excited-state aromaticity (ESA) is yet to make a big impact. The aim of this minireview is to illustrate the potential of this concept to become a key tool for the future design of photoswitches. The paper starts with a discussion of challenges facing the use of photoswitches for applications and continues with an account of how the ESA concept has progressed since its inception. Then, following some brief remarks on computational modeling of photoswitches and ESA, the paper describes two different approaches to improve the quantum yields and response times of switches driven by E/Z photoisomerization or photoinduced H-atom/proton transfer reactions through simple ESA considerations. It is our hope that these approaches, verified by quantum chemical calculations and molecular dynamics simulations, will help stimulate the application of the ESA concept as a general tool for designing more efficient photoswitches and other functional molecules used in optoelectronic devices.
TL;DR: Several new nitro-substituted adamantane compounds based on adamantane-1,3,5,7-tetrol were synthesized and the previously only briefly reported tetranitrate was reinvestigated.
Abstract: Several new nitro-substituted adamantane compounds based on adamantane-1,3,5,7-tetrol were synthesized and the previously only briefly reported tetranitrate was reinvestigated. The materials were completely characterized by spectroscopic methods including some by X-ray diffraction. The energetic properties, thermal stabilities, and sensitivities of the nitrocarbamate, nitrocarbamate salt, and nitrate were determined and compared to current composites in terms of potential high-energy dense oxidizers (HEDOs). Furthermore, the enthalpies of all compounds were calculated, and their energetic performances investigated by using the EXPLO5 code.
TL;DR: Interestingly, DSHILs possessed superior physicochemical properties such as relatively low viscosity or facilitated formation of micelles, which emphasizes the complex nature of multi-ion interactions in the microstructures of ionic liquid mixtures.
Abstract: In this study, two homologous series of novel herbicidal ionic liquids (HILs) were synthesized in a simple metathesis reaction between alkyl[2-(2-hydroxyethoxy)ethyl]dimethylammonium bromides and alkali metal salts of 4-chloro-2-methylphenoxyacetic acid (MCPA) or 3,6-dichloro-2-methoxybenzoic acid (dicamba), known as popular herbicides from the class of growth regulators. These HILs were subsequently mixed to prepare double-salt herbicidal ionic liquids (DSHILs). The DSHILs were characterized by substantially altered parameters of viscosity, refractive index, glass transition temperatures and surface activity compared to the average values expected for ideal mixtures of their individual components (HILs). Interestingly, DSHILs possessed superior physicochemical properties such as relatively low viscosity or facilitated formation of micelles, which emphasizes the complex nature of multi-ion interactions in the microstructures of ionic liquid mixtures. The biological tests showed improved efficiency of DSHILs against tested weeds compared to the reference herbicides and parent HILs.
TL;DR: The new gold catalyst was found to be highly active providing high to excellent yields of A3 coupling products via the reactions of various aldehydes, having electron-withdrawing as well as electron-donating substituents, with different amines and alkynes.
Abstract: We are grateful to the Institute for Advanced Studies in Basic Sciences (IASBS) Research Council and Iran National Science Foundation (INSF-Grant number of 95844587) for support of this study. C.N. is also thankful for financial support from the Spanish Ministerio de Economia y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), the Spanish Ministerio de Economia, Industria y Competitividad, Agencia Estatal de Investigacion (AEI), the Fondo Europeo de Desarrollo Regional (FEDER, EU) (projects CTQ2016-76782-P and CTQ2016-81797-REDC), the Generalitat Valenciana (PROMETEOII/2014/017), and the University of Alicante.
TL;DR: A new package, including polyurethane foam wrapped with superhydrophobic ZnO microrods/carbon cloth with long-life elasticity with excellent mechanical robustness and can be used several times for oil/water separation without capacity decrease was fabricated and was utilized for oil spill clean-up.
Abstract: A new package, including polyurethane foam wrapped with superhydrophobic ZnO microrods/carbon cloth with long-life elasticity, was fabricated and was utilized for oil spill clean-up. First, the carbon cloth (CC) was coated with ZnO microrods, which were modified with stearic acid (SA) to obtain superhydrophobic and superoleophilic properties. The coating process was conducted in mild conditions, involving the hydrothermal growth of ZnO microrods on the surface of the carbon cloth. The obtained hydrophobic sample was modified to a superhydrophobic one by adsorption of stearic acid (SA) on its surface. The prepared sample (CC/ZnO/SA) was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), and contact angle measurements. The prepared sample shows a water contact angle (WCA) of 160°. A piece of polyurethane foam was wrapped with the prepared superhydrophobic CC/ZnO/SA making an oil collecting package, which can float on the water surface and absorb various oils from the water surface in both static and turbulent conditions very quickly. The prepared package exhibits excellent mechanical robustness and can be used several times for oil/water separation without capacity decrease. The kinetics of oil spill absorption by the prepared package were studied, too.
TL;DR: In the context of the growing biological interest in metallarectangles, rectangle 4 was found to be highly active against two types of cancer cells, with IC50 values almost threefold superior to those of cisplatin.
Abstract: A new 4-ethynylpyridine 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based ligand L, which was synthesized by means of the Sonogashira coupling method, was used to obtain two new [2+2] iridium-based metallarectangles, 3 and 4. Ligand L and metallarectangles 3 and 4 were fully characterized through various analytical techniques. The structure of rectangle 4 was further confirmed by single-crystal X-ray diffraction analysis, which showed the formation of an expected [2+2] supramolecule, in which the iridium metal centers were bridged with ligand L to form the desired metallarectangle 4. In the context of the growing biological interest in metallarectangles, rectangle 4 was found to be highly active against two types of cancer cells, with IC50 values almost threefold superior to those of cisplatin. Both 3 and 4 showed dose-dependent abilities to bind bovine serum albumin and salmon sperm DNA; this indicated their tendency to interact with such biomolecules as a potential mode of action.
TL;DR: The effect of varying the dielectric constant on the performance of LEEC devices from ionic transition-metal complexes was studied by systematically exchanging the negative counterions paired with an iridium complex emitter.
Abstract: Light-emitting electrochemical cells (LEECs) are a promising low-cost option for display and solid-state lighting. In these devices, the interplay of mobile ions, electrons, and holes makes for rich physics that can be leveraged for high performance. One example of this interplay is in the formation and radiative decay of excitons-bound electron and hole pairs. Considerations from exciton binding and Langevin recombination suggest that a low dielectric constant (ϵ) would enhance emission. However, emission is also enhanced by the product of the bulk hole and electron concentrations, which in LEECs are enhanced by the motion of small mobile ions yielding high dielectric constants. These competing effects make it difficult to predict whether active layers with low or high dielectric constants will optimize device performance. Here, the effect of varying the dielectric constant on the performance of LEEC devices from ionic transition-metal complexes was studied by systematically exchanging the negative counterions paired with an iridium complex emitter. Electrochemical impedance spectroscopy, constant voltage and constant current device studies, and drift-diffusion simulations were performed. The results clarify the competing effects of Langevin bimolecular recombination and ion-assisted injection processes occurring in LEECs.
TL;DR: Photoluminescence study of the title compounds and Ba2 LaSbO6 was carried out, which confirmed that Eu3+ occupies distorted 12-coordinated A-site in BaLaMSbO 6 (M=Mg, Ca) and symmetrical octahedral B- site in Ba 2 LaS bO6 .
Abstract: Double perovskite antimonates of the type BaLaMSbO6 (M=Mg, Ca) were synthesized by a standard solid-state route. The compounds were characterized by X-ray crystallography and the structures were refined using Rietveld method. BaLaMgSbO6 and BaLaCaSbO6 crystallized in monoclinic space groups (I2/m) and (P21 /n), respectively. In both compounds, La occupied the A-site of perovskite, which is 12-coordinated as compared to Ba2 LaSbO6 where La ion shifts to the B-site octahedral coordination due to the larger size of Ba as compared with Mg and Ca. The samples were further characterized using FTIR and the frequency of the octahedral vibration is correlated to the electronegativity of the B-site ions. Photoluminescence study of the title compounds and Ba2 LaSbO6 was carried out upon doping with 2 atom% Eu3+ ion, which confirmed that Eu3+ occupies distorted 12-coordinated A-site in BaLaMSbO6 (M=Mg, Ca) and symmetrical octahedral B-site in Ba2 LaSbO6 . Furthermore, the emission spectrum corresponding to each Eu3+ ion at different crystal site was successfully isolated through a TRES study. This site selective occupancy of Eu3+ ion also has a direct impact on the light emission, which was found to change from orange to red in a dark room in the order Ba2 LaSbO6 : Eu→BaLaCaSbO6 : Eu→BaLaMgSbO6 : Eu. Such an outcome will have high impact in designing new commercial Eu3+ ion doped phosphor materials and tailoring of their optical properties.
TL;DR: The nascent concept of catalytic IL membranes is highlighted, in which catalytically active ILs/pILs are incorporated into membrane technologies to act as a catalytic separation layer.
Abstract: Membrane technologies enable the facile separation of complex mixtures of gases, vapours, liquids and/or solids under mild conditions. Simultaneous chemical transformations can also be achieved in membranes by using catalytically active membrane materials or embedded catalysts, in so-called membrane reactors. A particular class of membranes containing or composed of ionic liquids (ILs) or polymeric ionic liquids (pILs) have recently emerged. These membranes often exhibit superior transport and separation properties to those of classical polymeric membranes. ILs and pILs have also been extensively studied as separation solvents, catalysts and co-catalysts in similar applications for which membranes are employed. In this review, after introducing ILs and their applications in catalysis, catalytic membranes and recent advances in membrane separation processes based on ILs are described. Finally, the nascent concept of catalytic IL membranes is highlighted, in which catalytically active ILs/pILs are incorporated into membrane technologies to act as a catalytic separation layer.
TL;DR: Comparing the ability of several organic acids/choline chloride/water LTTMs to perform D-fructose dehydration to 5-hydroxymethylfurfural (5-HMF) seems to indicate a beneficial effect of chloride anions on D- fructose dehydration.
Abstract: The use of safe and sustainable solvents able to solvate reagents and to catalyze their reactions at temperatures below 100 °C is an innovative strategy to develop future lignocellulosic biorefineries. Many low-transition-temperature mixtures (LTTMs) have been investigated for this purpose. Among them, natural deep eutectic solvents (NADESs) have been proposed as cheap and renewable alternatives to ionic liquids for the synthesis of bio-based chemical building blocks. We compare herein the ability of several organic acids/choline chloride/water LTTMs to perform D-fructose dehydration to 5-hydroxymethylfurfural (5-HMF). The addition of chloride salts as well as an increased proportion of choline chloride promotes 5-HMF formation, which seems to indicate a beneficial effect of chloride anions on D-fructose dehydration. Besides improving selectivity by at least 10 %, increasing the choline chloride/acid ratio could enhance the biodegradability of the LTTMs. Unlike other acidic components, maleic and citric acids are especially selective at early D-fructose conversion. Maleic acid was the most selective acidic component among the tested chemicals, achieving an 80 % 5-HMF molar yield in 1 h at 90 °C.
TL;DR: It was found that a simple modification of the chain length induces a non-negligible effect on the emission properties, which must be linked to the specific arrangement of the fluorene units, which could open the way to modulation of properties of cyclofluorenes through alkyl chain engineering.
Abstract: Presented here is the study of a new example of [4]cyclofluorene, with ethyl chains on the bridgeheads. Its molecular structure was established by solution NMR spectroscopy and single-crystal X-ray diffraction. Three successive oxidation processes and one reversible reduction were observed through cyclic voltammetry. The optical properties were characterized both in solution and thin film by UV/visible spectroscopy as well as stationary and time-resolved fluorescence. It was found that this [4]cyclofluorene displays different characteristics compared with the other [4]cyclofluorenes substituted by methyl or propyl chains: a simple modification of the chain length induces a non-negligible effect on the emission properties, which must be linked to the specific arrangement of the fluorene units. Furthermore, single-crystal X-ray diffraction reveals the formation of a pseudo-tubular solid-state arrangement of fully symmetrical ring structures, which was not observed for the other members of the [4]cyclofluorenes family. This finding could open the way to modulation of properties of cyclofluorenes through alkyl chain engineering.
TL;DR: The results of this study indicate a promising new method to enhance the thermal stability of DSSCs using a nanocomposite anode made of one-dimensional carbon materials.
Abstract: In this study, the effect of incorporating multiwalled carbon nanotubes (MWCNTs) on the thermal stability of dye-sensitized solar cells (DSSCs) was investigated. Under identical measurement conditions (aging at 80 °C for 240 h), DSSCs based on a bare TiO2 anode presented a significant loss in photoconversion efficiency (PCE), dropping to 59 % of their initial value, whereas the DSSCs based on a TiO2 -MWCNT nanocomposite anode attained a promising thermal stability with only 20 % loss of PCE. This degradation of cell performance is mainly associated with a dramatic reduction in the short-circuit current density (Jsc ). To understand the mechanisms that underpin these changes in device performance under thermal stress, both types of cells were investigated using various techniques. The incorporation of MWCNTs could eliminate the formation of cracks and improve electron charge transfer. The results of this study indicate a promising new method to enhance the thermal stability of DSSCs using a nanocomposite anode made of one-dimensional carbon materials.
TL;DR: N nanostructured array based sensing platforms prepared from four widely used templates, a colloidal monolayer, anodic aluminum oxide, block copolymer, and a nanoimprint mold, are reviewed to demonstrate the morphological origin of the sensing performances.
Abstract: High sensitivity imposes strict requirements on a sensing platform, for which nanostructured arrays are promising candidates. The template-assisted method is an effective strategy to prepare various nanostructured arrays, which are widely developed for different sensing applications. Herein, nanostructured array based sensing platforms prepared from four widely used templates, a colloidal monolayer, anodic aluminum oxide, block copolymer, and a nanoimprint mold, are reviewed. In a series of sensing applications (e.g., biosensing and gas sensing), the resulting nanostructure-array-based platforms are high sensitive owing to their advanced morphology features: 1) high-density alignment of arrayed nanostructures, 2) high surface-to-volume ratio, and 3) convex-rich morphology. In surface-enhanced Raman spectroscopy (SERS) applications, noble-metal particle arrays with high-density alignment produce an enhanced SERS signal owing to a strong concentration of plasmonic resonance on the substrate. To sense biomolecules in solution and gaseous molecules, arrays with a high surface-to-volume ratio or convex-rich morphology can sensitively respond to changes in the environment. Moreover, the nanostructure-array-based sensing platforms are divided into three types (0D, 1D, and 3D nanostructured arrays) to demonstrate the morphological origin of the sensing performances.
TL;DR: The results suggest that the TADF dendrimer serving as an assistant dopant were helpful in reducing the triplet populations by up-converting the tripleT excitons to the singlet state and immediately transferring the singlets to Ir(bt)2 (acac) (bt=2-phenylbenzothiazolato, acac=acetylacetonato) by virtue of the long-range Förster resonance energy transfer.
Abstract: Thermally activated delayed fluorescence (TADF) emitters have received much attention for the fabrication of white organic light-emitting diodes (WOLEDs); however, challenges remain owing to severe efficiency roll-off, poor color stability, and high cost. In this contribution, solution-processed hybrid WOLEDs were obtained by employing a blue TADF dendrimer, bis{4-[3,6-bis(3,6-di-tert-butylcarbazol-N-yl)carbazol-N-yl]phenyl}sulfone (BPS), combined with an orange iridium complex, bis(2-phenylbenzothiazolato)(acetylacetonate)iridium(III), Ir(bt)2 (acac), as a co-dopant. The devices achieved a maximum external quantum efficiency of 6.59 % and a maximum current efficiency of 17.34 cd A-1 . The results suggest that the TADF dendrimer serving as an assistant dopant were helpful in reducing the triplet populations by up-converting the triplet excitons to the singlet state and immediately transferring the singlet excitons to Ir(bt)2 (acac) (bt=2-phenylbenzothiazolato, acac=acetylacetonato) by virtue of the long-range Forster resonance energy transfer, thus significantly decreasing the triplet-triplet annihilation (TTA). Moreover, the emitters can act as shallow trapping centers to decrease charge and exciton aggregation. The resulting OLEDs exhibit stable electroluminescent spectra and low efficiency roll-off at relatively high current density. The CIE coordinates Δ(x, y) vary only (0.02, 0.02) in the luminance range of 100 to 10 000 cd m-2 .
TL;DR: This Minireview uses relevant examples to put in perspective the utility of macrocyclic coordination chemistry for biological inorganic chemistry applications.
Abstract: 1,4,7-Triazacyclononane (TACN)-based mono- and poly-nuclear metal complexes have found extensive use as biological mimics for understanding the structural and operational aspects of complex natural systems. Their coordination flexibility has also provided researchers access to a vast library of radiometal-binding motifs that display excellent thermodynamic stability and kinetic inertness upon metal complexation. Synthetic modification of the TACN backbone has yielded ligands that can form metal complexes with coordination geometries well suited for these applications. In particular, Leone Spiccia's research has played a significant role in accelerating the progress in these two fields. With a focus on his contributions to the topics of biomimicry and radiopharmaceuticals, this Minireview uses relevant examples to put in perspective the utility of macrocyclic coordination chemistry for biological inorganic chemistry applications.
TL;DR: The fluorescence spectra and electrochemical measurement results suggest that the decorated FeP not only reduces the overpotential for H2 evolution but also promotes the separation of the photogenerated charge carriers through formation of a heterojunction with Zn0.5 Cd0.1-x S, which eventually leads to the superior activity of the FeP/Zn 0.5 S-P photocatalyst for visible-light-driven hydrogen generation.
Abstract: FeP as a noble-metal-free catalyst has been successfully decorated onto the Znx Cd1-x S photocatalyst surface through an in situ phosphating process. In particular, the 2 % FeP/Zn0.5 Cd0.5 S-P sample showed the best hydrogen generation activity of 24.45 mmol h-1 g-1 which is over 130 times higher than that of pure Zn0.5 Cd0.5 S and nearly 1.3 times higher than that of the 1 % Pt-loaded Zn0.5 Cd0.5 S-P sample. The apparent quantum yield (AQY) of the 2 % FeP/Zn0.5 Cd0.5 S-P was estimated to be over 10 % at wavelengths up to 470 nm. The fluorescence spectra and electrochemical measurement results suggest that the decorated FeP not only reduces the overpotential for H2 evolution but also promotes the separation of the photogenerated charge carriers through formation of a heterojunction with Zn0.5 Cd0.5 S, which eventually leads to the superior activity of the FeP/Zn0.5 Cd0.5 S-P photocatalyst for visible-light-driven hydrogen generation.
TL;DR: State-of-the-art femtosecond transient absorption measurements evidenced fast kinetics and dynamics in the singlet excited state in agreement with charge transfer processes promoted by excitation, with a proper ICT state observed in the case of C.
Abstract: The synthesis of three push-pull cationic dyes is reported here together with a photophysical study carried out by stationary and ultrafast spectroscopies The hyperpolarizability (β) values of the three molecules have been estimated through a simple solvatochromic method based on conventional, low-cost equipment, which had been tested previously with success in our laboratory The investigated pyridinium salts showing strong negative solvatochromism bear the same piperidine ring as a strong electron-donor group and the same thiophenes as electron-rich π-linkers, but differ in terms of the N-substituent on the electron-acceptor pyridinium unit, namely N-methyl in compound A, N-pyrimidin-2yl in B and N-2,4-dinitrophenyl in C The derived β values were found to increase (in the order A
TL;DR: Green light-emitting diodes prepared by using all-inorganic PeNPs CsPbBr3 synthesized at room temperature (RT) are reported and their performance compared with those prepared by a traditional hot-injection method.
Abstract: Perovskite nanoparticles (PeNPs) have been extensively studied for optoelectronic applications, owing to their extremely high photoluminescence quantum yield, tunable band gap, and exceptionally narrow emission spectra. Therefore, PeNPs are considered excellent candidates for the development of high-efficiency, low-cost, wide-gamut, and high-purity color displays. However, their synthesis typically involves multistep cumbersome processes that might hinder commercial development. Herein, green light-emitting diodes (LEDs) prepared by using all-inorganic PeNPs CsPbBr3 synthesized at room temperature (RT) are reported and their performance compared with those prepared by a traditional hot-injection method. Insights into the morphology and optoelectronic properties of RT PeNPs are provided through AFM and TEM and employing them in LEDs.
TL;DR: It was found that NPC derived from the core-shell MOF@MOF can provide excellent catalytic ORR performance exceeding that of the single MOF.
Abstract: Here we propose a new strategy in which two isomorphic metal-organic frameworks (MOFs) [FJU-40-H (a) and FJU-40-NH2 (b)] are used to construct the core-shell material MOF@MOF. This strategy based on nitrogen doping and specific surface has resulted in an N-doped porous carbon (NPC) material in a one-step thermal treatment in N2 atmosphere; this material displays high catalytic activity for the oxygen reduction reaction (ORR). The materials were analyzed by SEM, XPS, Raman, specific surface area, pore size distribution and electrochemical measurements. It was found that NPC derived from the core-shell MOF@MOF can provide excellent catalytic ORR performance exceeding that of the single MOF. The onset potential is NPC-b@a-4h (-0.068 V)>NPC-a@b-4h (-0.075 V)>NPC-a-4h (-0.109 V)>NPC-b-4h (-0.113 V). Moreover, the results also show that the performance of NPC-b@a (n=4.15) is better than that of NPC-a@b (n=3.32), which means the different nitrogen content of ligands inside and outside of the core affects the ORR properties.