Recent Progress of Thin Crystal Engineering for Perovskite Solar Cells.

Metal halide perovskite single crystals hold promise for photovoltaics with high efficiency and stability due to their superior optoelectronic properties and weak bulk ion migration. The past several years have witnessed rapid development of single-crystal perovskite solar cells (PSCs) with efficiency rocketed from 6.5% to 24.3%, however, which still lags behind their polycrystalline counterparts. Moreover, the poor device stability under light illumination is contrary to the high ion migration barrier of perovskite single crystals. The key limiting factors should be the low crystalline quality and high surface defect density of solution-grown thin single crystals. Under this circumstance, a review paper summarizing the recent progress and challenges will be instructive for future development of this emerging field. In this manuscript, the crystal engineering used to enhance carrier transport and suppress carrier recombination in vertical single-crystal PSCs will be summarized initially, including crystal growth, component control, surface and interface modification. Subsequently, the application of perovskite single crystals in lateral single-crystal PSCs will be discussed and compared with the conventionally vertical structure. Finally, the challenges and proposed strategies for the development of single-crystal PSCs are provided.

A Perspective on the Permeability of Cocrystals/Organic Salts of Oral Drugs.

According to the BCS classification system, the differentiation of drugs is based on two essential parameters of solubility and permeability, meaning the latter is as pivotal as the former in creating marketable pharmaceutical products. Nevertheless, the indispensable role of permeability in pharmaceutical cocrystal profiles has not been sufficiently cherished, which can be most probably attributed to two principal reasons. First, responsibility may be on more user-friendly in vitro measurement procedures for solubility compared to permeability, implying the permeability measurement process seems unexpectedly difficult for researchers, whereas they have a complete understanding of solubility concepts and experiments. Besides, it may be ascribed to the undeniable attraction of introducing new crystal-based structures which mostly leaves the importance of improving the function of existing multicomponents behind. Bringing in new crystalline entities, to rephrase it, researchers have a fairly better chance of achieving high-class publications. Although the Food and Drug Administration (FDA) has provided a golden opportunity for pharmaceutical cocrystals to straightforwardly enter the market by simply considering them as derivatives of the existing active pharmaceutical ingredients, inattention to assessing and scaling up permeability which is intimately linked with solubility has resulted in limited numbers of them in the global pharmaceutical market. Casting a glance at the future, it is apprehended that further development in the field of permeability of pharmaceutical cocrystals and organic salts requires a meticulous perception of achievements to date and potentials to come. Thence, this perspective scrutinizes the pathway of permeation assessment making researchers confront their fear upfront through mapping the simplest way of permeability measurement for multicomponents of oral drugs.

Crystal Engineering Under Residual Solvent Evaporation: A Journey Into Crystallization Chronicles of Soluble Acenes.

In the pursuit of achieving high-performance and high-throughput organic transistors, this study highlights two critical aspects: designing new soluble acenes and optimizing their solution processing. A fundamental understanding of the crystallization mechanism inherent to these customized soluble acenes, as they undergo a transformation during the evaporation of residual solvent, is deemed essential. Here, the pathway to crafting ideal solution processing conditions is elucidated, meticulously tailored to the molecular structure of soluble acenes when blended with polymers. Employing a comprehensive array of analytical and computational methodologies, this investigation delves directly into the intricate interplay between processing parameters and crystallization mechanisms, firmly rooted in the domains of thermodynamics and kinetics. Notably, a delicate equilibrium where the optimal weight of residual solvent harmoniously aligns is uncovered with the specific attributes of soluble acene molecules, exerting influence over vertical phase separation with the blended polymer and the crystallization process of soluble acenes at the surface. Consequently, transistors showcasing remarkable field-effect mobility exceeding 8 cm2 V-1 s-1 are successfully developed. These findings provide invaluable guidance for navigating the path toward determining optimal solution processing conditions across a diverse array of soluble acene/polymer blend systems, all achieved through the strategic application of crystal and residual solvent engineering.

Biocompatible Nano-Cocrystal Engineering for Targeted Herbicide Delivery: Enhancing Efficacy through Stimuli-Responsive Release and Reduced Environmental Losses.

In addressing the critical challenges posed by the misuse and inefficiency of traditional pesticides, we introduce a Nano-Cocrystal material composed of the herbicide clopyralid and coformer phenazine. Developed through synergistic supramolecular self-assembly and mechanochemical nanotechnology, this Nano-Cocrystal significantly enhances pesticide performance. It exhibits a marked improvement in stability, with reductions in hygroscopicity and volatility by approximately 38%. Moreover, it intelligently modulates release according to environmental factors, such as temperature, pH, and soil inorganic salts, demonstrating decreased solubility by up to four times and improved wettability and adhesion on leaf surfaces. Importantly, the herbicidal activity surpasses that of pure clopyralid, increasing suppression rates of Medicago sativa L. and Oxalis corniculata L. by up to 27% at the highest dosage. This Nano-Cocrystal also shows enhanced crop safety and reduced genotoxicity compared to conventional formulations. Offering a blend of simplicity, cost-effectiveness, and robust stability, our findings contribute a sustainable solution to agricultural practices, favoring the safety of nontarget organisms.

Dynamic Luminescence Vapochromism of Pyridinium-Based Organic Salts.

Organic vapochromic materials which undergo a drastic change in their photophysical properties upon exposure to vapors or gases are attracting growing scientific attention because of their low price and wide range of possible applications. In this work, luminescence vapochromism of carbazole-pyridinium-based organic salts with a general structure of (CzPy)X (CzPy+ = 2,3-di(9H-carbazol-9-yl)pyridinium ion; X = Cl, Br or I) is reported. It was found that (CzPy)X compounds form J-aggregates, which rearranged back to monomeric form upon exposure to methanol, ethanol, acetone, and water vapors. In contrast, acetonitrile was found to promote the J-aggregation in (CzPy)X compounds by occupying the voids in their crystal lattice and pushing cations closer together. It was further demonstrated that the efficiency of J-aggregation in (CzPy)X compounds depends on the size of the anion, which was employed to realize dynamic luminescence vapochromism, with vapochromic response times ranging from a couple of minutes in (CzPy)Cl to more than an hour in (CzPy)I. In addition, (CzPy)X compounds exhibited high melting points of about 250 °C and excellent thermal stability. (CzPy)Cl and (CzPy)Br have also shown good photoluminescence quantum yields at room temperature in a solid state.

Simultaneous Cycloadditions in the Solid State via Supramolecular Assembly.

Chemical reactions conducted in the solid phase (specifically, crystalline) are much less numerous than solution reactions, primarily due to reduced motion, flexibility, and reactivity. The main advantage of crystalline-state transformations is that reactant molecules can be designed to self-assemble into specific spatial arrangements, often leading to high control over product regiochemistry and/or stereochemistry. In crystalline-phase transformations, typically only one type of reaction occurs, and a sacrificial template molecule is frequently used to facilitate self-assembly, similar to a catalyst or enzyme. Here, we demonstrate the first system designed to undergo two chemically unique and orthogonal cycloaddition reactions simultaneously within a single crystalline solid. Well-controlled supramolecular self-assembly of two molecules containing different reactive moieties affords orthogonal reactivity without use of a sacrificial template. Using only UV light, the simultaneous [2+2] and [4+4] cycloadditions are achieved regiospecifically, stereospecifically, and products are obtained in high yield, whereas a simultaneous solution-state reaction affords a mixture of isomers in low yield. Application of dually-reactive systems toward (supra)molecular solar thermal storage materials is also discussed. This work demonstrates fundamental chemical approaches for orthogonal reactivity in the crystalline state and highlights the complexity and reversibility that can be achieved with supramolecular design.

A crystal engineering approach for rational design of curcumin crystals for Pickering stabilization of emulsions.

Emulsions stabilized via Pickering particles are becoming more and more popular due to their high stability and biocompatibility. Hence, developing new ways to produce effective Pickering particles is essential. In this work, we present a crystal engineering approach to obtain precise control over particle properties such as size, shape, and crystal structure, which may affect wettability and surface chemistry. A highly reproducible synthesis method via anti-solvent crystallization was developed to produce sub-micron sized curcumin crystals of the metastable form III, to be used as Pickering stabilizers. The produced crystals presented a clear hydrophobic nature, which was demonstrated by their preference to stabilize water-in-oil (W/O) emulsions. A comprehensive experimental and computational characterization of curcumin crystals was performed to rationalize their hydrophobic nature. Analytical techniques including Raman spectroscopy, powder X-ray diffraction (PXRD), Solid-State Nuclear Magnetic Resonance (SSNMR), scanning electron microscopy (SEM), Differential Scanning Calorimetry (DSC), confocal fluorescence microscopy and contact angle measurements were used to characterize curcumin particles in terms of shape, size and interfacial activity. The attachment energy model was instead applied to study relevant surface features of curcumin crystals, such as topology and facet-specific surface chemistry. This work contributes to the understanding of the effect of crystal properties on the mechanism of Pickering stabilization, and paves the way for the formulation of innovative products in fields ranging from pharmaceuticals to food science.

High-Efficiency Inverted Perovskite Solar Cells via In Situ Passivation Directed Crystallization.

Lead halide perovskite solar cells (PSCs) have emerged as one of the influential photovoltaic technologies with promising cost-effectiveness. Though with mild processabilities to massive production, inverted PSCs have long suffered from inferior photovoltaic performances due to intractable defective states at boundaries and interfaces. Herein, an in situ passivation (ISP) method is presented to effectively adjust crystal growth kinetics and obtain the well-orientated perovskite films with the passivated boundaries and interfaces, successfully enabled the new access of high-performance inverted PSCs. The study unravels that the strong yet anisotropic ISP additive adsorption between different facets and the accompanied additive engineering yield the high-quality (111)-orientated perovskite crystallites with superior photovoltaic properties. The ISP-derived inverted perovskite solar cells (PSCs) have achieved remarkable power conversion efficiencies (PCEs) of 26.7% (certified as 26.09% at a 5.97 mm2 active area) and 24.5% (certified as 23.53% at a 1.28 cm2 active area), along with decent operational stabilities.

Size Reduction to Enhance Crystal-to-Liquid Phase Transition Induced by E-to-Z Photoisomerization Based on Molecular Crystals of Phenylbutadiene Ester.

Harnessing the photoinduced phase transitions in organic crystals, especially the changes in shape and structure across various dimensions, offers a fascinating avenue for exact spatiotemporal control, which is crucial for developing future smart devices. In our study, we report a new photoactive molecular crystal made from (E)-2-(3-phenyl-allylidene)malonate ((E)-PADM). When exposed to ultraviolet (UV) light at 365 nm, this compound experiences an E-to-Z photoisomerization in liquid solution and a crystal-to-liquid phase transition in solid crystals. Remarkably, nanoscopic crystalline rods boost their melting rate and degree compared to bulk crystals, indicating that miniaturization enhances the photoinduced melting effect. Our results demonstrate a simple approach to rapidly drive molecular crystals into liquids via photochemical reactions and phase transitions.

Solvatomorphism in a series of copper(II) complexes with the 5-phenylimidazole/perchlorate system as ligands.

In the course of an investigation of the supramolecular behaviour of copper(II) complexes with the 5-phenylimidazole/perchlorate ligand system (`blend') remarkable solvatomorphism has been observed. By employing a variety of crystallization solvents (polar protic, polar/non-polar aprotic), a series of 12 crystalline solvatomorphs with the general formula [Cu(ClO4)2(LH)4]·x(solvent) have been obtained [LH = 5-phenylimidazole, x(solvent) = 3.3(H2O) (1), 2(methanol) (2), 2(ethanol) (3), 2(1-propanol) (4), 2(2-propanol) (5), 2(2-butanol) (6), 2(dimethylformamide) (7), 2(acetone) (8), 2(tetrahydrofurane) (9), 2(1,4-dioxane) (10), 2(ethyl acetate) (11) and 1(diethyl ether) (12)]. The structures have been solved using single-crystal X-ray diffraction and the complexes were characterized by thermal analysis and infrared spectroscopy. The solvatomorphs are isostructural (triclinic, P1), with the exception of compound 9 (monoclinic, P21/n). The supramolecular structures and the role of the various solvents is discussed. All potential hydrogen-bond functionalities, both of the [Cu(ClO4)2(LH)4] units and of the solvents, are utilized in the course of the crystallization process. The supramolecular assembly in all structures is directed by strong recurring Nimidazole-H...Operchlorate motifs leading to robust scaffolds composed of the [Cu(ClO4)2(LH)4] host complexes. The solvents are located in channels and, with the exception of the disordered waters in 1 and the diethyl ether in 12, participate in hydrogen-bonding formation with the [Cu(ClO4)2(LH)4] complexes, serving as both hydrogen-bond acceptors and donors (for the polar protic solvents in 2-6), or solely as hydrogen-bond acceptors (for the polar/non-polar aprotic solvents in 7-11), linking the complexes and contributing to the stability of the crystalline compounds.

Structure-property relationship of a complex photoluminescent arylacetylide-gold(I) compound. I: a pressure-induced phase transformation caught in the act.

A pressure-induced triclinic-to-monoclinic phase transition has been caught `in the act' over a wider series of high-pressure synchrotron diffraction experiments conducted on a large, photoluminescent organo-gold(I) compound. Here, we describe the mechanism of this single-crystal-to-single-crystal phase transition, the onset of which occurs at ∼0.6 GPa, and we report a high-quality structure of the new monoclinic phase, refined using aspherical atomic scattering factors. Our case illustrates how conducting a fast series of diffraction experiments, enabled by modern equipment at synchrotron facilities, can lead to overestimation of the actual pressure of a phase transition due to slow transformation kinetics.

Symmetry-Breaking and Symmetry-Retaining Morphological Evolution of the Single Crystals of Cyclodextrin Metal-Organic Frameworks.

The morphological symmetry-retaining and symmetry-breaking of single crystals of the γ-cyclodextrin metal-organic framework have been achieved via introducing lower symmetric ß-cyclodextrins and α-cyclodextrins, respectively. ß-cyclodextrins led to a morphological evolution with retained symmetry from cubic to rhombic dodecahedra, while α-cyclodextrins resulted in the original cubic crystal missing a vertex angle presenting symmetry-breaking behavior. The crystal structures of rhombic dodecahedra and angle-deficient crystals were confirmed through X-ray crystallography, and the mechanisms underlying the morphological transformation evolution were further analyzed. Our work not only provides a rare case realizing two different paths of morphological evolution in one system, but also encourages future efforts towards the evolution of artificial crystal systems in a natural way.

Large Local Internal Stress in an Elastically Bent Molecular Crystal Revealed by Raman Shifts.

The structural dynamics involved in the mechanical flexibility of molecular crystals and the internal stress in such flexible materials remain obscure. Here, the study reports an elastically bending lipidated molecular crystal that shows systematic shifts in characteristic vibrational frequencies across the bent crystal region - revealing the nature of structural changes during bending and the local internal stress distribution. The blueshifts in the bond stretching modes (such as C═O and C-H modes) in the inner arc region and redshifts in the outer arc region of the bent crystals observed via micro-Raman mapping are counterintuitive to the bending models based on intermolecular hydrogen bonds. Correlating these shifts with the trends observed from high-pressure Raman studies on the crystal reveals the local stress difference between the inner arc and outer arc regions of the bent crystal to be ≈2 GPa, more than an order of magnitude higher than the previously proposed value in elastically bending crystals. High local internal stress can have direct ramifications on the properties of molecular piezoelectric energy harvesters, actuators, semiconductors, and flexible optoelectronic materials.

Chemistry and crystal engineering.

Recent studies published in the Chemistry and crystal engineering section of IUCrJ emphasize developments both in methodology and techniques as well as the diverse range of classes of compounds being studied and of problems being tackled.

Exhaled Anesthetic Xenon Regeneration by Gas Separation Using a Metal-Organic Framework with Sorbent-Sorbate Induced-Fit.

Noble gas xenon (Xe) is an excellent anesthetic gas, but its rarity, high cost and constrained production prohibits wide use in medicine. Here, we have developed a closed-circuit anesthetic Xe recovery and reusage process with highly effective CO2-specific adsorbent CUPMOF-5 that is promising to solve the anesthetic Xe supply problem. CUPMOF-5 possesses spacious cage cavities interconnected in four directions by confinement throat apertures of ~3.4 Å, which makes it an ideal molecular sieving of CO2 from Xe, O2, N2 with the benchmark selectivity and high uptake capacity of CO2. In situ single-crystal X-ray diffraction (SCXRD) and computational simulation solidly revealed the vital sieving role of the confined throat and the sorbent-sorbate induced-fit strengthening binding interaction to CO2. CUPMOF-5 can remove 5 % CO2 even from actual moist exhaled anesthetic gases, and achieves the highest Xe recovery rate (99.8 %) so far, as verified by breakthrough experiments. This endows CUPMOF-5 great potential for the on-line CO2 removal and Xe recovery from anesthetic closed-circuits.

Electrostatic Surface Potentials and Chalcogen-Bonding Motifs of Substituted 2,1,3-Benzoselenadiazoles Probed via 77Se Solid-State NMR Spectroscopy.

Chalcogen bonds (ChB) are moderately strong, directional, and specific non-covalent interactions that have garnered substantial interest over the last decades. Specifically, the presence of two σ-holes offers great potential for crystal engineering, catalysis, biochemistry, and molecular sensing. However, ChB applications are currently hampered by a lack of methods to characterize and control chalcogen bonds. Here, we report on the influence of various substituents (halogens, cyano, and methyl groups) on the observed self-complementary ChB networks of 2,1,3-benzoselenadiazoles. From molecular electrostatic potential calculations, we show that the electrostatic surface potentials (ESP) of the σ-holes on selenium are largely influenced by the electron-withdrawing character of these substituents. Structural analyses via X-ray diffraction reveal a variety of ChB geometries and binding modes that are rationalized via the computed ESP maps, although the structure of 5,6-dimethyl-2,1,3-benzoselenadiazole also demonstrates the influence of steric interactions. 77Se solid-state magic-angle spinning NMR spectroscopy, in particular the analysis of the selenium chemical shift tensors, is found to be an effective probe able to characterize both structural and electrostatic features of these self-complementary ChB systems. We find a positive correlation between the value of the ESP maxima at the σ-holes and the experimentally measured 77Se isotropic chemical shift, while the skew of the chemical shift tensor is established as a metric which is reflective of the ChB binding motif.

Investigating the Mechanism of Triboluminescence: Insights from Structural and Electrostatic Characterization of Copper Thiocyanate Complexes.

Triboluminescence is a phenomenon in which light is generated through mechanical stress; it has emerging applications in stress-sensing devices. Although the prevailing mechanistic model indicates that light emits from charge separation and recombination in fracture planes arising from polar structures, its application in designing triboluminescent materials remains limited owing to numerous exceptions. This study provides insights into the essential requirements for triboluminescence by investigating the structural and electrostatic properties of fractured crystals of copper thiocyanate complexes. The examined fracture plane indicated that charge pairs (which are essential for light emission) form when intermolecular interactions are disrupted during fracturing. On the basis of the nature of these charges, we successfully suppressed triboluminescence by inhibiting the formation of intermolecular interactions disrupted in the examined complexes. Furthermore, we induced its re-emergence by creating an alternative fracture plane through controlled manipulation of the molecular network. This demonstrative deactivation and reactivation of triboluminescence underscores the critical role of intermolecular disruption in generating charge pairs, a prerequisite for triboluminescence.

The Continuous and Reversible Transformation of the Polymorphs of an MGAT2 Inhibitor (S-309309) from the Anhydrate to the Hydrate in Response to Relative Humidity.

Polymorphic control is vital for the quality control of pharmaceutical crystals. Here, we investigated the relationship between the hydrate and anhydrate polymorphs of a monoacylglycerol acyltransferase 2 inhibitor (S-309309). Solvent evaporation and slurry conversion revealed two polymorphs, the hydrate and the solvate. The solvate was transformed into the hydrate by heating. X-ray powder diffraction demonstrated that the hydrate was transformed into an anhydrate via an intermediate state when heated. These crystal forms were confirmed under controlled humidity conditions; the presence of the anhydrate, the intermediate hydrate, or the hydrate depended on the relative humidity at 25 °C. The stoichiometry of S-309309 in water in the hydrate form was 4:1. The hydrates and anhydrates exhibited similar crystal structures and stability. The water of hydration in the intermediate hydrate was 0.1-0.15 mol according to the dynamic vapor sorption profile. The stability and dissolution profile of the anhydrate and hydrate showed no significant change due to similar crystal lattices and quick rehydration of the anhydrate. A mechanism for the reversible crystal transformation between the anhydrate and pseudo-polymorphs of the hydrate was discovered. We concluded that S-309309 causes a pseudo-polymorphic transformation; however, this is not a critical issue for pharmaceutical use.

Modulation of Water Vapor Sorption by Pore Engineering in Isostructural Square Lattice Topology Coordination Networks.

We report a crystal-engineering study conducted upon a platform of three mixed-linker square lattice (sql) coordination networks of general formula [Zn(Ria)(bphy)] [bphy = 1,2-bis(pyridin-4-yl)hydrazine, H2Ria = 5-position-substituted isophthalic acid, and R = -Br, -NO2, and -OH; compounds 1-3]. Analysis of single-crystal X-ray diffraction data of 1-2 and the simulated crystal structure of 3 revealed that 1-3 are isomorphous and sustained by bilayers of sql networks linked by hydrogen bonds. Although similar pore shapes and sizes exist in 1-3, distinct isotherm shapes (linear and S shape) and uptakes (2.4, 11.6, and 13.3 wt %, respectively) were observed. Ab initio calculations indicated that the distinct water sorption properties can be attributed to the R groups, which offer a range of hydrophilicity. Calculations indicated that the significantly lower experimental uptake in compound 1 can be attributed to a constricted channel. The calculated water-binding sites provide insights into how adsorbed water molecules bond to the pore walls, with the strongest interactions, water-hydroxyl hydrogen bonding, observed for 3. Overall, this study reveals how pore engineering can result in large variations in water sorption properties in an isomorphous family of rigid porous coordination networks.

Improving the Solubility and Bioavailability of Progesterone Cocrystals with Selected Carboxylic Acids.

Progesterone (PROG) is a natural steroid hormone with low solubility and high permeability that belongs to biopharmaceutics classification system class II. In this study, novel pharmaceutical cocrystals of PROG were successfully prepared by solvent evaporation or a liquid-assisted grinding process aimed at enhancing its solubility and bioavailability. The cocrystal formers selected based on crystal engineering principles were carboxylic acids, namely, 4-formylbenzeneboronic acid (BBA), isophthalic acid (IPA), and 3-nitrophthalic acid (NPA). The cocrystal structures were characterized using multiple techniques. Single-crystal X-ray diffraction results showed that the carbonyl group, acting as a hydrogen bond acceptor, was pivotal in the cocrystal network formation, with C-H···O interactions further stabilizing the crystals. The cocrystals exhibited improved solubility and dissolution profiles in vitro, with no significant changes in hygroscopicity. The parallel artificial membrane permeability assay (PAMPA) models indicated that the cocrystals retained PROG's high permeability. Pharmacokinetic studies in Sprague-Dawley rats revealed that all cocrystals increased PROG exposure, with AUC(0~∞) values for PROG-BBA, PROG-IPA, and PROG-NPA being 742.59, 1201.72 and 442.67 h·ng·mL-1, respectively. These values are substantially higher compared to free PROG, which had an AUC(0~∞) of 301.48 h·ng·mL-1. Notably, PROG-IPA provided the highest AUC improvement, indicating a significant enhancement in bioavailability. Collectively, the study concludes that the cocrystal approach is a valuable strategy for optimizing the physicochemical properties and oral bioavailability of PROG, with potential implications for the development of other poor water-soluble drugs.