Thiocyanate-Stabilized Pseudo-cubic Perovskite CH(NH2)2PbI3 from Coincident Columnar Defect Lattices.

α-FAPbI3 (FA+ = CH(NH2)2+) with a cubic perovskite structure is promising for photophysical applications. However, α-FAPbI3 is metastable at room temperature, and it transforms to the δ-phase at a certain period of time at room temperature. Herein, we report a thiocyanate-stabilized pseudo-cubic perovskite FAPbI3 with ordered columnar defects (α'-phase). This compound has a √5ap × âˆš5ap × ap tetragonal unit cell (ap: cell parameter of primitive perovskite cell) with a band gap of 1.91 eV. It is stable at room temperature in a dry atmosphere. Furthermore, the presence of the α'-phase in a mixed sample with the δ-phase drastically reduces the δ-to-α transition temperature measured on heating, suggesting the reduction of the nucleation energy of the α-phase or thermodynamic stabilization of the α-phase through epitaxy. The defect-ordered pattern in the α'-phase forms a coincidence-site lattice at the twinned boundary of the single crystals, thus hinting at an epitaxy- or strain-based mechanism of α-phase formation and/or stabilization. In this study, we developed a new strategy to control defects in halide perovskites and provided new insight into the stabilization of α-FAPbI3 by pseudo-halide and grain boundary engineering.

Correlating Broadband Photoluminescence with Structural Dynamics in Layered Hybrid Halide Perovskites.

The emission of white light from a single material is atypical and is of interest for solid-state lighting applications. Broadband light emission has been observed in some layered perovskite derivatives, A2PbBr4 (A = R-NH3+), and correlates with static structural distortions corresponding to out-of-plane tilting of the lead bromide octahedra. While materials with different organic cations can yield distinct out-of-plane tilts, the underlying origin of the octahedral tilting remains poorly understood. Using high energy resolution (e.g., quasi-elastic) neutron scattering, this contribution details the rotational dynamics of the organic cations in A2PbBr4 materials where A = n-butylammonium (nBA), 1,8-diaminooctammonium (ODA), and 4-aminobutyric acid (GABA). The organic cation dynamics differentiate (nBA)2PbBr4 from (ODA)PbBr4 or (GABA)2PbBr4 in that the larger spatial extent of dynamics of nBA yields a larger effective cation radius. The larger effective volume of the nBA cation in (nBA)2PbBr4 yields a closer to ideal A-site geometry, preventing the out-of-plane tilt and broadband luminescence. In all three compounds, we observe hydrogen dynamics attributed to rotation of the ammonium headgroup and at a time scale faster than the white light photoluminescence studied by time-correlated single photon counting spectroscopy. This supports a previous assignment of the broadband emission as resulting from a single ensemble, such that the emissive excited state experiences many local structures faster than the emissive decay. The findings presented here highlight the role of the organic cation and its dynamics in hybrid organic-inorganic perovskites and white light emission.

Chemical and Toxicological Characterization of Vaping Emission Products from Commonly Used Vape Juice Diluents.

Recent reports have linked severe lung injuries and deaths to the use of e-cigarettes and vaping products. Nevertheless, the causal relationship between exposure to vaping emissions and the observed health outcomes remains to be elucidated. Through chemical and toxicological characterization of vaping emission products, this study demonstrates that during vaping processes, changes in chemical composition of several commonly used vape juice diluents (also known as cutting agents) lead to the formation of toxic byproducts, including quinones, carbonyls, esters, and alkyl alcohols. The resulting vaping emission condensates cause inhibited cell proliferation and enhanced cytotoxicity in human airway epithelial cells. Notably, substantial formation of the duroquinone and durohydroquinone redox couple was observed in the vaping emissions from vitamin E acetate, which may be linked to acute oxidative stress and lung injuries reported by previous studies. These findings provide an improved molecular understanding and highlight the significant role of toxic byproducts in vaping-associated health effects.

Structure and Optical Properties of Layered Perovskite (MA)2PbI2-xBrx(SCN)2 (0 ≤ x < 1.6).

The layered perovskite (MA)2PbI2(SCN)2 (MA = CH3NH3+) is a member of an emerging series of compounds derived from hybrid organic-inorganic perovskites. Here, we successfully synthesized (MA)2PbI2-xBrx(SCN)2 (0 ≤ x < 1.6) by using a solid-state reaction. Despite smaller bromide substitution for iodine, 1% linear expansion along the a axis was observed at x ∼ 0.4 due to a change of the orientation of the SCN- anions. Diffuse reflectance spectra reveal that the optical band gap increases by the bromide substitution, which is supported by the DFT calculations. Curiously, bromine-rich compounds where x ≥ 0.8 are light sensitive, leading to partial decomposition after ∼24 h. This study demonstrates that the layered perovskite (MA)2PbI2(SCN)2 tolerates a wide range of bromide substitution toward tuning the band gap energy.

Casting a Wider Net: Rational Synthesis Design of Low-Dimensional Bulk Materials.

The discovery of novel magnetic and electronic properties in low-dimensional materials has led to the pursuit of hierarchical materials with specific substructures. Low-dimensional solids are highly anisotropic by nature and show promise in new quantum materials leading to exotic physical properties not realized in three-dimensional materials. We have the opportunity to extend our synthetic strategy of the flux-growth method to designing single crystalline low-dimensional materials in bulk. The goal of this Account is to highlight the synthesis and physical properties of several low-dimensional intermetallic compounds containing specific structural motifs that are linked to desirable magnetic and electrical properties. We turned our efforts toward intermetallic compounds consisting of antimony nets because they are closely linked to properties such as high carrier mobility (the velocity of an electron moving through a material under a magnetic field) and large magnetoresistance (the change in resistivity with an applied magnetic field), both of which are desirable properties for technological applications. The SmSb2 structure type is of particular interest because it is comprised of rectangular antimony nets and rare earth ions stacked between the antimony nets in a square antiprismatic environment. LnSb2 (Ln = La-Nd, Sm) have been shown to be highly anisotropic with SmSb2 exhibiting magnetoresistance of over 50000% for H∥c axis and ∼2400% for H∥ab. Using this structure type as an initial building block, we envision the insertion of transition metal substructures into the SmSb2 structure type to produce ternary materials. We describe compounds adopting the HfCuSi2 structure type as an insertion of a tetrahedral transition metal-antimony subunit into the LnSb2 host structure. We studied LnNi1-xSb2 (Ln = Y, Gd-Er), where positive magnetoresistance reaching above 100% was found for the Y, Gd, and Ho analogues. We investigated the influence of the transition metal sublattice by substituting Ni into Ce(Cu1-xNix)ySb2 (y < 0.8) and found that the material is highly anisotropic and metamagnetic transitions appear at ∼0.5 and 1 T in compounds with higher Ni concentration. Metamagnetism is characterized by a sharp increase in the magnetic response of a material with increasing applied magnetic field, which was also observed in LnSb2 (Ln = Ce-Nd). We also endeavored to study materials that possess a transition metal sublattice with the potential for geometric frustration. An example is the La2Fe4Sb5 structure type, which consists of antimony square nets and an iron-based network arranged in nearly equilateral triangles, a feature found in magnetically frustrated systems. We discovered spin glass behavior in Ln2Fe4Sb5 (Ln = La-Nd, Sm) and evidence that the transition metal sublattice contributes to the magnetic interactions of Ln2Fe4Sb5. We investigated the magnetic properties of Pr2Fe4-xCoxSb5 (x < 2.3) and found that as the Co concentration increases, a second magnetic transition leads from a localized to an itinerant system. The La2Fe4Sb5 structure type is quite robust and allows for the incorporation of other transition metals, thereby making it an excellent candidate to study competing magnetic interactions in lanthanide-containing intermetallic compounds. In this manuscript, we aim to share our experiences of bulk intermetallic compounds to inspire the development of new low-dimensional materials.

Hybrid Charge-Transfer Semiconductors: (C7H7)SbI4, (C7H7)BiI4, and Their Halide Congeners.

Hybrid metal halides yield highly desirable optoelectronic properties and offer significant opportunity due to their solution processability. This contribution reports a new series of hybrid semiconductors, (C7H7)MX4 (M = Bi3+, Sb3+; X = Cl-, Br-, I-), that are composed of edge-sharing MX6 chains separated in space by π-stacked tropylium (C7H7+) cations; the inorganic chains resemble the connectivity of BiI3. The Bi3+ compounds have blue-shifted optical absorptions relative to the Sb3+ compounds that span the visible and near-IR region. Consistent with observations, DFT calculations reveal that the conduction band is composed of the tropylium cation and valence band primarily the inorganic chain: a charge-transfer semiconductor. The band gaps for both Bi3+ and Sb3+ compounds decrease systematically as a function of increasing halide size. These compounds are a rare example of charge-transfer semiconductors that also exhibit efficient crystal packing of the organic cations, thus providing an opportunity to study how structural packing affects optoelectronic properties.

Water cluster confinement and methane adsorption in the hydrophobic cavities of a fluorinated metal-organic framework.

Water cluster formation and methane adsorption within a hydrophobic porous metal organic framework is studied by in situ vibrational spectroscopy, adsorption isotherms, and first-principle DFT calculations (using vdW-DF). Specifically, the formation and stability of H2O clusters in the hydrophobic cavities of a fluorinated metal-organic framework (FMOF-1) is examined. Although the isotherms of water show no measurable uptake (see Yang et al. J. Am. Chem. Soc. 2011 , 133 , 18094 ), the large dipole of the water internal modes makes it possible to detect low water concentrations using IR spectroscopy in pores in the vicinity of the surface of the solid framework. The results indicate that, even in the low pressure regime (100 mTorr to 3 Torr), water molecules preferentially occupy the large cavities, in which hydrogen bonding and wall hydrophobicity foster water cluster formation. We identify the formation of pentameric water clusters at pressures lower than 3 Torr and larger clusters beyond that pressure. The binding energy of the water species to the walls is negligible, as suggested by DFT computational findings and corroborated by IR absorption data. Consequently, intermolecular hydrogen bonding dominates, enhancing water cluster stability as the size of the cluster increases. The formation of water clusters with negligible perturbation from the host may allow a quantitative comparison with experimental environmental studies on larger clusters that are in low concentrations in the atmosphere. The stability of the water clusters was studied as a function of pressure reduction and in the presence of methane gas. Methane adsorption isotherms for activated FMOF-1 attained volumetric adsorption capacities ranging from 67 V(STP)/V at 288 K and 31 bar to 133 V(STP)/V at 173 K and 5 bar, with an isosteric heat of adsorption of ca. 14 kJ/mol in the high temperature range (288-318 K). Overall, the experimental and computational data suggest high preferential uptake for methane gas relative to water vapor within FMOF-1 pores with ease of desorption and high framework stability under operative temperature and moisture conditions.

Cannabidiol and cannabis-inspired terpene blends have acute prosocial effects in the BTBR mouse model of autism spectrum disorder.

Introduction: Cannabidiol (CBD) is a non-intoxicating phytocannabinoid with increasing popularity due to its purported therapeutic efficacy for numerous off-label conditions including anxiety and autism spectrum disorder (ASD). Those with ASD are commonly deficient in endogenous cannabinoid signaling and GABAergic tone. CBD has a complex pharmacodynamic profile that includes enhancing GABA and endocannabinoid signaling. Thus, there is mechanistic justification for investigating CBD's potential to improve social interaction and related symptoms in ASD. Recent clinical trials in children with ASD support CBD's beneficial effects in numerous comorbid symptoms, but its impact on social behavior is understudied. Methods: Here, we tested the prosocial and general anxiolytic efficacy of a commercially available CBD-rich broad spectrum hemp oil delivered by repeated puff vaporization and consumed via passive inhalation in the female cohort of the BTBR strain, a common inbred mouse line for preclinical assessment of ASD-like behaviors. Results: We observed that CBD enhanced prosocial behaviors using the 3-Chamber Test with a different vapor dose-response relationship between prosocial behavior and anxiety-related behavior on the elevated plus maze. We also identified that inhalation of a vaporized terpene blend from the popular OG Kush cannabis strain increased prosocial behavior independently of CBD and acted together with CBD to promote a robust prosocial effect. We observed similar prosocial effects with two additional cannabis terpene blends from the Do-Si-Dos and Blue Dream strains, and further reveal that these prosocial benefits rely on the combination of multiple terpenes that comprise the blends. Discussion: Our results illustrate the added benefit of cannabis terpene blends for CBD-based treatment of ASD.

Minor, Nonterpenoid Volatile Compounds Drive the Aroma Differences of Exotic Cannabis.

Cannabis sativa L. produces a wide variety of volatile secondary metabolites that contribute to its unique aroma. The major volatile constituents include monoterpenes, sesquiterpenes, and their oxygenated derivates. In particular, the compounds ß-myrcene, D-(+)-limonene, ß-caryophyllene, and terpinolene are often found in greatest amounts, which has led to their use in chemotaxonomic classification schemes and legal Cannabis sativa L. product labeling. While these compounds contribute to the characteristic aroma of Cannabis sativa L. and may help differentiate varieties on a broad level, their importance in producing specific aromas is not well understood. Here, we show that across Cannabis sativa L. varieties with divergent aromas, terpene expression remains remarkably similar, indicating their benign contribution to these unique, specific scents. Instead, we found that many minor, nonterpenoid compounds correlate strongly with nonprototypical sweet or savory aromas produced by Cannabis sativa L. Coupling sensory studies to our chemical analysis, we derive correlations between groups of compounds, or in some cases, individual compounds, that produce many of these diverse scents. In particular, we identified a new class of volatile sulfur compounds (VSCs) containing the 3-mercaptohexyl functional group responsible for the distinct citrus aromas in certain varieties and skatole (3-methylindole) as the key source of the chemical aroma in others. Our results provide not only a rich understanding of the chemistry of Cannabis sativa L. but also highlight how the importance of terpenes in the context of the aroma of Cannabis sativa L. has been overemphasized.

Identification of a New Family of Prenylated Volatile Sulfur Compounds in Cannabis Revealed by Comprehensive Two-Dimensional Gas Chromatography.

Cannabis sativa L. produces over 200 known secondary metabolites that contribute to its distinctive aroma. Studies on compounds traditionally associated with the scent of this plant have focused on those within the terpenoid class. These isoprene-derived compounds are ubiquitous in nature and are the major source of many plant odors. Nonetheless, there is little evidence that they provide the characteristic "skunk-like" aroma of cannabis. To uncover the chemical origins of this scent, we measured the aromatic properties of cannabis flowers and concentrated extracts using comprehensive two-dimensional gas chromatography equipped with time-of-flight mass spectrometry, flame ionization detection, and sulfur chemiluminescence. We discovered a new family of volatile sulfur compounds (VSCs) containing the prenyl (3-methylbut-2-en-1-yl) functional group that is responsible for this scent. In particular, the compound 3-methyl-2-butene-1-thiol was identified as the primary odorant. We then conducted an indoor greenhouse experiment to monitor the evolution of these compounds during the plant's lifecycle and throughout the curing process. We found that the concentrations of these compounds increase substantially during the last weeks of the flowering stage, reach a maximum during curing, and then drop after just one week of storage. These results shed light on the chemical origins of the characteristic aroma of cannabis and how volatile sulfur compound production evolves during plant growth. Furthermore, the chemical similarity between this new family of VSCs and those found in garlic (allium sativum) suggests an opportunity to also investigate their potential health benefits.

Influence of organic cation planarity on structural templating in hybrid metal-halides.

Controlling the connectivity and topology of solids is a versatile way to target desired physical properties. This is especially relevant in the realm of hybrid halide semiconductors, where the long-range connectivity of the inorganic substructural unit can lead to significant changes in optoelectronic properties such as photoluminescence, charge transport, and absorption. We present a new series of hybrid metal-halide semiconductors, (phenH2)BiI5·H2O, (2,2-bpyH2)BiI5, (BrbpyH)BiI4·H2O, (phenH2)2Pb3I10·2H2O, and (2,2-bpyH2)2Pb3I10 where (phenH2)2+ = 1,10-phenanthroline-1,10-diium, (2,2-bpyH2)2+ = 2,2'-bipyridine-1,1'-diium and (BrbpyH)+ = 6,6'-dibromo-2,2'-bipyridium. These compounds allow us to observe how the planarity of the cation, induced either through structural modification in the case of (phenH2)2+ or through non-covalent interactions in (BrbpyH)+, both relative to (2,2-bpyH2)2+, modifies the inorganic substructural unit. While the Pb2+ series of compounds show minimal changes in inorganic connectivity, we observe large differences in the Bi3+ series, ranging from 0-D dimers to corner- and edge-sharing 1-D chains of octahedra. We find that compounds containing (phenH2)2+ and (BrbpyH)+ pack more efficiently than those with (2,2-bpyH2)2+ due to their retention of planarity leading to greater inorganic connectivity. Electronic structure calculations and optical diffuse reflectance reveal that the band gaps of these compounds are influenced by the degree of inorganic connectivity and the inorganic substructural unit distances. These results show that the structure and planarity of organic cations can directly influence both the inorganic connectivity and the optical properties that could be tuned for certain optoelectronic applications.

Systematic Control of the Orientation of Organic Phosphorescent Pt Complexes in Thin Films for Increased Optical Outcoupling.

Orienting light-emitting molecules relative to the substrate is an effective method to enhance the optical outcoupling of organic light-emitting devices. Platinum(II) phosphorescent complexes enable facile control of the molecular alignment due to their planar structures. Here, the orientation of Pt(II) complexes during the growth of emissive layers is controlled by two different methods: modifying the molecular structure and using structural templating. Molecules whose structures are modified by adjusting the diketonate ligand of the Pt complex, dibenzo-(f,h)quinoxaline Pt dipivaloylmethane, (dbx)Pt(dpm), show an ≈20% increased fraction of horizontally aligned transition dipole moments compared to (dbx)Pt(dpm) doped into a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl, CBP, host. Alternatively, a template composed of highly ordered 3,4,9,10-perylenetetracarboxylic dianhydride monolayers is predeposited to drive the alignment of a subsequently deposited emissive layer comprising (2,3,7,8,12,13,17,18-octaethyl)-21H,23H-porphyrinplatinum(II) doped into triindolotriazine. This results in a 60% increase in horizontally aligned transition dipole moments compared to the film deposited in the absence of the template. The findings provide a systematic route for controlling molecular alignment during layer growth, and ultimately to increase the optical outcoupling in organic light-emitting diodes.

Synthetic control over orientational degeneracy of spacer cations enhances solar cell efficiency in two-dimensional perovskites.

Two-dimensional perovskites have emerged as more intrinsically stable materials for solar cells. Chemical tuning of spacer organic cations has attracted great interest due to their additional functionalities. However, how the chemical nature of the organic cations affects the properties of two-dimensional perovskites and devices is rarely reported. Here we demonstrate that the selection of spacer cations (i.e., selective fluorination of phenethylammonium) affects the film properties of two-dimensional perovskites, leading to different device performance of two-dimensional perovskite solar cells (average n = 4). Structural analysis reveals that different packing arrangements and orientational disorder of the spacer cations result in orientational degeneracy and different formation energies, largely explaining the difference in film properties. This work provides key missing information on how spacer cations exert influence on desirable electronic properties and device performance of two-dimensional perovskites via the weak and cooperative interactions of these cations in the crystal lattice.

Adsorption and molecular siting of CO2, water, and other gases in the superhydrophobic, flexible pores of FMOF-1 from experiment and simulation.

FMOF-1 is a flexible, superhydrophobic metal-organic framework with a network of channels and side pockets decorated with -CF3 groups. CO2 adsorption isotherms measured between 278 and 313 K and up to 55 bar reveal a maximum uptake of ca. 6.16 mol kg-1 (11.0 mol L-1) and unusual isotherm shapes at the higher temperatures, suggesting framework expansion. We used neutron diffraction and molecular simulations to investigate the framework expansion behaviour and the accessibility of the small pockets to N2, O2, and CO2. Neutron diffraction in situ experiments on the crystalline powder show that CO2 molecules are favourably adsorbed at three distinct adsorption sites in the large channels of FMOF-1 and cannot access the small pockets in FMOF-1 at 290 K and oversaturated pressure at 61 bar. Stepped adsorption isotherms for N2 and O2 at 77 K can be explained by combining Monte Carlo simulations in several different crystal structures of FMOF-1 obtained from neutron and X-ray diffraction under different conditions. A similar analysis is successful for CO2 adsorption at 278 and 283 K up to ca. 30 bar; however, at 298 K and pressures above 30 bar, the results suggest even more substantial expansion of the FMOF-1 framework. The measured contact angle for water on an FMOF-1 pellet is 158°, demonstrating superhydrophobicity. Simulations and adsorption measurements also show that FMOF-1 is hydrophobic and water is not adsorbed in FMOF-1 at room temperature. Simulated mixture isotherms of CO2 in the presence of 80% relative humidity predict that water does not influence the CO2 adsorption in FMOF-1, suggesting that hydrophobic MOFs could hold promise for CO2 capture from humid gas streams.

A non-doped phosphorescent organic light-emitting device with above 31% external quantum efficiency.

The demonstrated square-planar Pt(II)-complex has reduced triplet-triplet quenching and therefore a near unity quantum yield in the neat thin film. A non-doped phosphorescent organic light-emitting diode (PhOLED) based on this emitter achieves (31.1 ± 0.1)% external quantum efficiency without any out-coupling, which shows that a non-doped PhOLED can be comparable in efficiency to the best doped devices with very complicated device structures.