The double perovskite family, A2MIMIIIX6, is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH3NH3PbI3. Given the generally large indirect ...band gap within most known double perovskites, band‐gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs2AgBiBr6 as host, band‐gap engineering through alloying of InIII/SbIII has been demonstrated in the current work. Cs2Ag(Bi1−xMx)Br6 (M=In, Sb) accommodates up to 75 % InIII with increased band gap, and up to 37.5 % SbIII with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs2Ag(Bi0.625Sb0.375)Br6. Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three‐metal systems are also assessed.
Unleaded: The substituted double perovskites, Cs2Ag(Bi1−xInx)Br6 (x=0, 0.25, 0.5, and 0.75) and Cs2Ag(Bi1−xSbx)Br6 (x=0, 0.125, and 0.375), were successfully synthesized. The band gap can be tuned from 1.86 eV to 2.27 eV, associated with broad photoluminescence from visible to near‐infrared. Band structure calculations provide insight into the band gap engineering in these alloys, and environmental stability was assessed over a two‐month period.
π-Extended pyrene compounds possess remarkable luminescent and semiconducting properties and are being intensively investigated as electroluminescent materials for potential uses in organic ...light-emitting diodes, transistors, and solar cells. Here, the synthesis of two sets of pyrene-containing π-conjugated polyaromatic regioisomers, namely 2,3,10,11,14,15,20,21-octaalkyloxypentabenzo
,
,
,
,
pentaphene (
) and 2,3,6,7,13,14,17,18-octaalkyloxydibenzo
,
phenanthro 9,10-
picene (
), is reported. They were obtained using the Suzuki-Miyaura cross-coupling in tandem with Scholl oxidative cyclodehydrogenation reactions from the easily accessible precursors 1,8- and 1,6-dibromopyrene, respectively. Both sets of compounds, equipped with eight peripheral aliphatic chains, self-assemble into a single hexagonal columnar mesophase, with one short-chain
homolog also exhibiting another columnar mesophase at a lower temperature, with a rectangular symmetry;
isomers also possess wider mesophase ranges and higher mesophases' stability than their
homologs. These polycyclic aromatic hydrocarbons all show a strong tendency of face-on orientation on the substrate and could be controlled to edge-on alignment through mechanical shearing of interest for their implementation in photoelectronic devices. In addition, both series
and
display green-yellow luminescence, with high fluorescence quantum yields, around 30%. In particular,
exhibit a blue shift phenomenon in both absorption and emission with respect to their
isomers. DFT results were in good agreement with the optical properties and with the stability ranges of the mesophases by confirming the higher divergence from the flatness of
compared with
. Based on these interesting properties, these isomers could be potentially applied not only in the field of fluorescent dyes but also in the field of organic photoelectric semiconductor materials as electron transport materials.
Recently, CuI‐ and AgI‐based halide double perovskites have been proposed as promising candidates for overcoming the toxicity and instability issues inherent within the emerging Pb‐based halide ...perovskite absorbers. However, up to date, only AgI‐based halide double perovskites have been experimentally synthesized; there are no reports on successful synthesis of CuI‐based analogues. Here we show that, owing to the much higher energy level for the Cu 3d10 orbitals than for the Ag 4d10 orbitals, CuI atoms energetically favor 4‐fold coordination, forming CuX4 tetrahedra (X=halogen), but not 6‐fold coordination as required for CuX6 octahedra. In contrast, AgI atoms can have both 6‐ and 4‐fold coordinations. Our density functional theory calculations reveal that the synthesis of CuI halide double perovskites may instead lead to non‐perovskites containing CuX4 tetrahedra, as confirmed by our material synthesis efforts.
Tetrahedra preferred: Owing to the high‐energy level for the Cu 3d10 orbitals, CuI atoms energetically do not favor the 6‐fold coordination required for CuX6 octahedra. DFT and experimental studies reveal that the CuI halide double perovskites are thermodynamically unstable against decomposition into products containing CuX4 tetrahedra.
High levels of cholesterol are generally considered to be associated with atherosclerosis. In the past two decades, however, a number of studies have shown that excess cholesterol accumulation in ...various tissues and organs plays a critical role in the pathogenesis of multiple diseases. Here, we summarize the effects of excess cholesterol on disease pathogenesis, including liver diseases, diabetes, chronic kidney disease, Alzheimer’s disease, osteoporosis, osteoarthritis, pituitary-thyroid axis dysfunction, immune disorders, and COVID-19, while proposing that excess cholesterol-induced toxicity is ubiquitous. We believe this concept will help broaden the appreciation of the toxic effect of excess cholesterol, and thus potentially expand the therapeutic use of cholesterol-lowering medications.
Here, Song et al. present a concept called “cholesterol toxicity,” which stems from the emerging evidence of adverse effects of excess cholesterol in multiple organs. They suggest that excess cholesterol contributes to the pathogenesis of several diseases other than atherosclerosis. This concept potentially expands the therapeutic use of cholesterol-lowering medications.
Recently, there has been substantial interest in developing double-B-cation halide perovskites, which hold the potential to overcome the toxicity and instability issues inherent within emerging lead ...halide-based solar absorber materials. Among all double perovskites investigated, In(I)-based Cs2InBiCl6 and Cs2InSbCl6 have been proposed as promising thin-film photovoltaic absorber candidates, with computational examination predicting suitable materials properties, including direct bandgap and small effective masses for both electrons and holes. In this study, we report the intrinsic instability of Cs2In(I)M(III)X6 (M = Bi, Sb; X = halogen) double perovskites by a combination of density functional theory and experimental study. Our results suggest that the In(I)-based double perovskites are unstable against oxidation into In(III)-based compounds. Further, the results show the need to consider reduction–oxidation (redox) chemistry when predicting stability of new prospective electronic materials, especially when less common oxidation states are involved.
Two series of regio-isomeric butterfly-shaped liquid crystalline systems, based on a ditriphenylenothiophene core (α/β-DTPT) equipped with eight peripheral long alkoxy chains, were synthesized in two ...steps by the Suzuki–Miyaura cross-coupling/Scholl cyclo-dehydrogenation reactions tandem from appropriate precursors. The influence of the core topology ( i.e. positional isomerism) on the mesomorphism, gelling self-assembly, absorption and luminescence, and charge-transport properties of both sets of isomers was investigated and compared. The six fused π-conjugated molecules systematically display columnar hexagonal (Col hex ) mesophases with β-fused ditriphenylenothiophene compounds (DTPTBn) showing more extended mesophase ranges and higher phase transition temperatures than their isomeric α-counterparts (DTPTAn). All ditriphenylenothiophenes also show strong aggregation behavior in organic solvents, and, in addition, good organic gelling abilities were found for the β-isomers. Interestingly too, high hole mobility rates greater than 10 −3 cm 2 V −1 s −1 were measured for the β-isomers, which were about 10 times higher than those of the α-counterparts. Modeling of the molecular structures combined with DFT calculations showed that the β-isomers possess flatter and more extended π-conjugated cores than the slightly distorted α-isomers, and consequently were more prone to optimize π–π intermolecular interactions, in agreement with the high-temperature mesophases and high charge carrier mobilities observed for these isomers. Finally, both sets of compounds emit blue-purple light in solution and the emission is substantially red-shifted when organized in films. DFT calculations of the HOMO–LUMO energy levels were also consistent with the optical measurements. This original molecular design and straightforward synthesis combination provides an efficient way to obtain novel π-extended organic, potentially semiconductor materials for further electronic device investigations.
Covering: 2009 to 2018.
Diterpenoid alkaloids, originating from the amination of natural tetracyclic diterpenes, are a diverse class of compounds having complex structural features with many ...stereocenters. The important pharmacological activities and structural complexity of the diterpenoid alkaloids have long interested scientists due to their medicinal uses, infamous toxicity, and unique biosynthesis. Since 2009, 373 diterpenoid alkaloids, assigned to 46 skeletons, have been isolated and identified from plants mostly in the Ranunculaceae family. The names, classes, molecular weight, molecular formula, NMR data, and plant sources of these diterpene alkaloids are collated here. This review will be a detailed update of the naturally occurring diterpene alkaloids reported from the plant kingdom from 2009-2018, providing an in-depth discussion of their diversity, biological activities, pharmacokinetics, toxicity, application, evolution, and biosynthesis.
Diterpenoid alkaloids, originating from the amination of natural tetracyclic diterpenes, are a diverse class of compounds having complex structural features with many stereocenters.
The synthesis of an exclusive family of liquid-crystalline dimers consisting of two protomesogenic triphenylene moieties connected
via
a rigid, π-conjugated bridge, and the study of their ...mesomorphous, gel self-assembly and optical properties as a function of the nature of the bridge are reported. Various triphenylene bridged dimers were successfully prepared by either palladium-catalyzed Suzuki-Miyaura cross-coupling between pentakis(alkoxy)triphenylene nonaflates and various commercially accessible aryldiboronic acids (as bridges) or by FeCl
3
-promoted Scholl oxidative homo-coupling of thiophene/thienothiophene/furan-containing pentakis(alkoxy)triphenylene derivatives. All linear dimers are mesomorphous, and self-organize into large multi-columnar rectangular superlattices, with columnar pairs arranged according to a chevron-like pattern, as deduced from SWAXS and supported by STM. At high temperature, most compounds also display a nematic columnar mesophase (N
Col
), easily recognized by characteristic optical textures. The transition temperature and mesophase ranges show a high dependency on the bridge nature and, to a lesser extent, on the chain-lengths around the triphenylene moieties. The sole kinked bridged-dimeric homolog of this series exhibits a single, room-temperature hexagonal mesophase (Col
hex
), as do the monofunctionalized triphenylene precursors, whereas the dimeric triphenylene with no bridge is not mesomorphous. UV-visible absorption and fluorescence emission spectra were measured in both solvents and thin films. The π-conjugated bridged-dimers exhibit emission spanning from 400-700 nm, thus covering the full visible-light range, whose emission maxima are obviously influenced by the chemical nature of the bridge. Furthermore, fluorescence quantum yields as high as 64% were measured for some of them. DFT theoretical computing calculations fully support the experimental measurements. Most dimers also form gels in cyclohexane and emit blue-to-orange light when irradiated by UV light; the corresponding xerogels revealed that their gelation ability results from the 3D morphology of entangled ultra-long and thin microfibers. The facile synthesis of these unique, multifunctional rigid discotic dimers, their rich mesomorphism, strong gelation ability and fine-tuned photophysical properties make these materials very attractive for the active field of organic electronics.
π-Conjugated liquid-crystalline dimers consisting of two triphenylene mesogens connected through a rigid molecular bridge have been synthesized. Mesophases, gels and optical properties have been investigated as a function of the bridge nature.
Uranium is important in the nuclear fuel cycle both as an energy source and as radioactive waste. It is of vital importance to recover uranium from nuclear waste solutions for further treatment and ...disposal. Herein we present the first chalcogenide example, (Me2NH2)1.33(Me3NH)0.67Sn3S7·1.25H2O (FJSM-SnS), in which organic amine cations can be used for selective UO2 2+ ion-exchange. The UO2 2+-exchange kinetics perfectly conforms to pseudo-second-order reaction, which is observed for the first time in a chalcogenide ion-exchanger. This reveals the chemical adsorption process and its ion-exchange mechanism. FJSM-SnS has excellent pH stability in both strongly acidic and basic environments (pH = 2.1–11), with a maximum uranium-exchange capacity of 338.43 mg/g. It can efficiently capture UO2 2+ ions in the presence of high concentrations of Na+, Ca2+, or HCO3 – (the highest distribution coefficient K d value reached 4.28 × 104 mL/g). The material is also very effective in removing of trace levels of U in the presence of excess Na+ (the relative amounts of U removed are close to 100%). The UO2 2+···S2– interactions are the basis for the high selectivity. Importantly, the uranyl ion in the exchanged products could be easily eluted with an environmentally friendly method, by treating the UO2 2+-laden materials with a concentrated KCl solution. These advantages coupled with the very high loading capacity, low cost, environmentally friendly nature, and facile synthesis make FJSM-SnS a new promising remediation material for removal of radioactive U from nuclear waste solutions.
A series of two-dimensional (2D) hybrid organic–inorganic perovskite (HOIP) crystals, based on acene alkylamine cations (i.e., phenylmethylammonium (PMA), 2-phenylethylammonium (PEA), ...1-(2-naphthyl)methanammonium (NMA), and 2-(2-naphthyl)ethanammonium (NEA)) and lead(II) halide (i.e., PbX4 2–, X = Cl, Br, and I) frameworks, and their corresponding thin films were fabricated and examined for structure–property relationship. Several new or redetermined crystal structures are reported, including those for (NEA)2PbI4, (NEA)2PbBr4, (NMA)2PbBr4, (PMA)2PbBr4, and (PEA)2PbI4. Non-centrosymmetric structures from among these 2D HOIPs were confirmed by piezoresponse force microscopyespecially noteworthy is the structure of (PMA)2PbBr4, which was previously reported as centrosymmetric. Examination of the impact of organic cation and inorganic layer choice on the exciton absorption/emission properties, among the set of compounds considered, reveals that perovskite layer distortion (i.e., Pb–I–Pb bond angle between adjacent PbI6 octahedra) has a more global effect on the exciton properties than octahedral distortion (i.e., variation of I–Pb–I bond angles and discrepancy among Pb–I bond lengths within each PbI6 octahedron). In addition to the characteristic sharp exciton emission for each perovskite, (PMA)2PbCl4, (PEA)2PbCl4, (NMA)2PbCl4, and (PMA)2PbBr4 exhibit separate, broad “white” emission in the long wavelength range. Piezoelectric compounds identified from these 2D HOIPs may be considered for future piezoresponse-type energy or electronic applications.
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