Stacking Of Molecules Research Articles

Hydrothermal synthesis, crystal structure and photoluminescent properties of 2D layered zinc phosphate intercalated with 4,4ˈbiphenyl dicarboxylic acid (ZnPO-BDA)

Herein, we report a new inorganic-organic hybrid, (H3tren)2⸱[Zn3(PO4)4(BDA)]⸱xH2O (ZnPO-BDA) prepared under hydrothermal conditions. This hybrid structure of zinc phosphate layers pillared with 4,4′-biphenyl-dicarboxylic acid (BDA) was characterized by single-crystal X-ray diffraction. The compound, ZnPO-BDA, crystallizes in the monoclinic crystal system (space group C2) with a = 14.9348(3) Å, b = 8.7058(2) Å, c = 17.6455(5) Å, β = 111.6760(10), V = 2132.02(9) Å3, Z = 2. The crystalline host of the 2D zinc phosphate framework was built with vertex linked ZnO4 and PO4 tetrahedra and anchored with tris(2-aminoethyl)amine (H3tren). Biphenyl dicarboxylic acid (BDA) molecules stack between the phosphate framework layers by means of strong hydrogen bonding, resulting in an interlayer distance of 16.4 Å. ZnPO-BDA displayed blue photoluminescence with an emission maximum at 404 nm on photoexcitation at 340 nm.

105 K Wide Room Temperature Spin Transition Memory Due to a Supramolecular Latch Mechanism

Little is known about the mechanisms behind the bistability (memory) of molecular spin transition compounds over broad temperature ranges (>100 K). To address this point, we report on a new discrete FeII neutral complex [FeIIL2]0 (1) based on a novel asymmetric tridentate ligand 2-(5-(3-methoxy-4H-1,2,4-triazol-3-yl)-6-(1H-pyrazol-1-yl))pyridine (L). Due to the asymmetric cone-shaped form, in the lattice, the formed complex molecules stack into a one-dimensional (1D) supramolecular chain. In the case of the rectangular supramolecular arrangement of chains in methanolates 1-A and 1-B (both orthorhombic, Pbcn) differing, respectively, by bent and extended spatial conformations of the 3-methoxy groups (3MeO), a moderate cooperativity is observed. In contrast, the hexagonal-like arrangement of supramolecular chains in polymorph 1-C (monoclinic, P21/c) results in steric coupling of the transforming complex species with the peripheral flipping 3MeO group. The group acts as a supramolecular latch, locking the huge geometric distortion of complex 1 and in turn the trigonal distortion of the central FeII ion in the high-spin state, thereby keeping it from the transition to the low-spin state over a large thermal range. Analysis of the crystal packing of 1-C reveals significantly changing patterns of close intermolecular interactions on going between the phases substantiated by the energy framework analysis. The detected supramolecular mechanism leads to a record-setting robust 105 K wide hysteresis spanning the room temperature region and an atypically large TLIESST relaxation value of 104 K of the photoexcited high-spin state. This work highlights a viable pathway toward a new generation of cleverly designed molecular memory materials.

Modulation of the Fluorination Site on Side-Chain Thiophene Improved Efficiency in All-Small-Molecule Organic Solar Cells.

Fine-tuning the phase-separated morphology is of great importance to achieve efficient all-small-molecule organic solar cells (ASM-OSCs). In this work, a pair of isomers are designed and synthesized, namely, BDT-UF and BDT-DF, in which the fluorine atom in BDT-UF is close to the alkyl chain of side-chain thiophene, while that in BDT-DF is close to the center core. Owing to the noncovalent interaction between fluorine and hydrogen, BDT-DF shows a smaller dihedral angle between the thiophene side chain and the BDT core, which causes better molecular planarity. When mixed with N3, BDT-UF shows better miscibility, higher crystallinity, and more ordered molecule stacking in the blend film. Finally, the device of BDT-DF:N3 gains a power conversion efficiency (PCE) of 14.5%, while that of BDT-UF:N3 shows an increase in Voc, Jsc, and FF and gains a PCE of 15.1%. Our work exhibits a way of adjusting the substitution site of fluorine atoms to improve the PCE of ASM-OSCs.

New graphitic carbon nitride-based composite membranes: Fast water transport through the synergistic effect of tannic acid and tris(hydroxymethyl) aminomethane

Graphitic carbon nitride nanosheets can be assembled into two-dimensional layered separation membranes due to their unique structure; however, the narrow interlayer channels (0.32 nm) cause strong transmembrane mass transfer resistance. In this study, we expanded the interlayer spacing by intercalating tris(hydroxymethyl) aminomethane (Tris) molecules as supports while introducing high-affinity and adhesive tannic acid (TA) molecules to suppress the disordered stacking of Tris molecules. The two were stably anchored between the layers through hydrogen bonding to form an interlayer channel of 0.83 nm. While maintaining the high rejection performance (>99%) for EB dyes, the improved composite membrane possessed an ultrahigh water flux (170 ± 6 L h−1 m−2 bar−1) that was more than ten times higher than that of the pristine g-C3N4 membrane. We also studied the acid-base resistance, organic solvent resistance and mechanical stability of the composite membrane.

Constructing Effective Hole Transport Channels in Cross-Linked Hole Transport Layer by Stacking Discotic Molecules for High Performance Deep Blue QLEDs.

The inadequate hole injection limits the efficiency and lifetime of the blue quantum dot light‐emitting diodes (QLEDs), which severely hampers their commercial applications. Here a new discotic molecule of 3,6,10,11‐tetrakis(pentyloxy)triphenylene‐2,7‐diyl bis(2,2‐dimethylpropanoate) (T5DP‐2,7) is introduced, in which the hole transport channels with superior hole mobility (2.6 × 10–2 cm2 V–1 s–1) is formed by stacking. The composite hole transport material (HTM) is prepared by blending T5DP‐2,7 with the cross‐linked 4,4′‐ bis(3‐vinyl‐9H‐carbazol‐9‐yl)‐1,1′biphenyl (CBP‐V) which shows the deep highest occupied molecular orbital energy level. The increased hole mobility of the target composite HTM from 10–4 to 10–3 cm2 V–1 s–1 as well as the stepwise energy levels facilitates the hole transport, which would be beneficial for more balanced carrier injection. This composite hole transport layer (HTL) has improved the deep‐blue‐emission performances of Commission International de I'Eclairage of (0.14, 0.04), luminance of 44080 cd m−2, and external quantum efficiency of 18.59%. Furthermore, when L0 is 100 cd m−2, the device lifetime T50 is extended from 139 to 502 h. The state‐of‐the‐art performance shows the successful promotion of the high‐efficiency for deep blue QLEDs, and indicates that the optimizing HTL by discotic molecule stacking can serve as an excellent alternative for the development of HTL in the future.

Dual-state emission of a coumarin acylhydrazone pH dye as colorimetric and fluorometric dual-channel indicator for seafood spoilage taggant

A coumarin hydrazone ligand 1 not only displays a dual-state emission but also has an ability to behave as a solid-state fluorescent sensor for vapor detection of volatile acid and ammonia (1 = 7-(diethylamino)-2-oxo-N′-(pyridin-2-ylmethylene)-2H-chromene-3-carbohydrazide). The mechanism of “OFF” fluorescent signal of conjugate acid of 1 (H1+) is due to the formation of H-aggregate with aggregation-caused quenching (ACQ) effect, however, molecule stacking of protonated counterpart H1+·ClO4·DCE with staircase arrangement of J-aggregates exhibited an orange emission in the solid state, acting as crystallization-induced emission (CIE) active nature. Moreover, the color and fluorescence emission of CIE-active molecule can be switched by external stimuli including grinding and solvent vapor. Utilizing the excellent OFF–ON response to HCl-NH3 vapor in the solid state, H1+ acts as a colorimetric and fluorometric dual-channel indicator upon exposure to total basic volatile nitrogen (TVB-N) compounds from fish as it spoils. The freshness of different batches, species and temperatures of fillets were readily monitored using standard chemometric and fluorometric approaches, providing in situ quality assurance (QA) information for fisheries industries and consumers.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Crystal Structures and Conducting Properties of Mott Insulator (BEDT-BDS)PF6: Selenium Substitution Effect in the Parent (BEDT-BDT)PF6

Abstract A new organic donor, viz. benzo[1,2-g:4,5-g′]bis(seleno[2,3-b][1,4]dithiin) (BEDT-BDS), which is a selenium analog of the parent benzo[1,2-g:4,5-g′]bis(thieno[2,3-b][1,4]dithiin), has been synthesized. The degree of “zigzag-N-shaped” molecular bending of BEDT-BDS, which is caused by the selenium substitution, is greater than that of BEDT-BDT. The N-shaped molecular bending in a radical-cation salt (BEDT-BDS)PF6 changes the S⋯S contact distances between the stacked molecules, and thus, a quasi-one-dimensional electronic structure is formed. According to the compositional formula and temperature dependence of resistivity, the PF6 salt is revealed to be a half-filled Mott insulator.

Pyrene‐Based Dopant‐Free Hole‐Transport Polymers with Fluorine‐Induced Favorable Molecular Stacking Enable Efficient Perovskite Solar Cells

AbstractA new class of polymeric hole‐transport materials (HTMs) are explored by inserting a two‐dimensionally conjugated fluoro‐substituted pyrene into thiophene and selenophene polymeric chains. The broad conjugated plane of pyrene and “Lewis soft” selenium atoms not only enhance the π–π stacking of HTM molecules greatly but also render a strong interaction with the perovskite surface, leading to an efficient charge transport/transfer in both the HTM layer and the perovskite/HTM interface. Note that fluorine substitution adjacent to pyrene boosts the stacking of HTMs towards a more favorable face‐on orientation, further facilitating the efficient charge transport. As a result, perovskite solar cells (PSCs) employing PE10 as dopant‐free HTM afford an excellent efficiency of 22.3 % and the dramatically enhanced device longevity, qualifying it among the best PSCs based on dopant‐free HTMs.

Pyrene-Based Dopant-Free Hole-Transport Polymers with Fluorine-Induced Favorable Molecular Stacking Enable Efficient Perovskite Solar Cells.

A new class of polymeric hole‐transport materials (HTMs) are explored by inserting a two‐dimensionally conjugated fluoro‐substituted pyrene into thiophene and selenophene polymeric chains. The broad conjugated plane of pyrene and “Lewis soft” selenium atoms not only enhance the π–π stacking of HTM molecules greatly but also render a strong interaction with the perovskite surface, leading to an efficient charge transport/transfer in both the HTM layer and the perovskite/HTM interface. Note that fluorine substitution adjacent to pyrene boosts the stacking of HTMs towards a more favorable face‐on orientation, further facilitating the efficient charge transport. As a result, perovskite solar cells (PSCs) employing PE10 as dopant‐free HTM afford an excellent efficiency of 22.3 % and the dramatically enhanced device longevity, qualifying it among the best PSCs based on dopant‐free HTMs.

An ultrasensitive fluorescent breath ammonia sensor for noninvasive diagnosis of chronic kidney disease and helicobacter pylori infection

Breath ammonia detection has been a significant non-invasive approach for disease diagnosis. However, the reported methods for breath ammonia detection suffer from high cost, time-consuming, complex operation, or low selectivity. Fluorescence analysis as an alternative method has not been introduced in the detection of breath ammonia due to its insufficient sensitivity. In this work, a rationally designed strategy is proposed to improve the sensitivity of fluorescence sensors by increasing the amount of recognition site and enhancing the brightness of the solid-state fluorescence in sensor molecule. Briefly, three curcumin (CUR) derivatives BFCUR, MBFCUR and MBFCURM with D-π-A-π-D conjugated system were synthesized. Compared with the other two control molecules MBFCUR and MBFCURM, whose phenol groups at one or both ends of BFCUR were protected by a methyl group, BFCUR has two response sites, thus, two intramolecular charge transfer (ICT) interactions occurred after exposure to ammonia, suggesting the improved sensitivity. Moreover, the large steric hindrance of boron trifluoride in BFCUR can prevent the π-π stacking of molecules and endow BFCUR with bright solid-state fluorescence. BFCUR was subsequently loaded into electrospun nanofibers (ENFs) with high specific surface area, which further improved the detection sensitivity. The obtained BFCUR-loaded ENFs sensor (denoted as BFCUR-ENF) exhibited ultra-low LOD of 22 ppb for ammonia. BFCUR-ENF is successfully applied to breath ammonia detection in healthy volunteers, patients with chronic kidney disease (CKD) and Helicobacter pylori (H. pylori) infection, demonstrating its great application potentials. Taken together, the first fluorescent sensor for breath ammonia detection was successfully constructed for noninvasive diagnosis of CKD and H. pylori.

Preparation of highly selective reverse osmosis membranes by introducing a nonionic surfactant in the organic phase

The development of highly selective polyamide (PA) membranes is critical for improving the quality and efficiency of the reverse osmosis (RO) process. However, the preparation of highly selective RO membranes exhibits some limitations, such as low efficiency and complex preparation process. Herein, RO membranes with high selectivity were prepared by adding Tween 80, a nonionic surfactant, to an organic phase. The state of Tween 80 in the organic phase and its function in the interfacial polymerization process were thoroughly discussed based on the detailed characterization of the organic phase solution and membrane. Furthermore, the optimization of the Tween 80 concentration, organic phase temperature, organic solvent type, and heat treatment temperature enabled the preparation of a membrane with high rejection (99.61%), high water flux (40.28 L m−2 h−1), and high stability. Compared with the virgin membrane, the selectivity of the optimized membrane increased by 136% and its permeability decreased by only 23%. In summary, the nonionic surfactant Tween 80 reacted with trimesoyl chloride (TMC) in the developed membrane preparation method to produce a new product TW-TMC, exhibiting a dual role of a surfactant and a co-monomer in the interfacial polymerization process, thereby regulating the formation and stacking of PA molecules.

Size-dependent filling effect of crystalline celluloses in structural engineering of composite oleogels

Oleogels are a class of solid-fat mimetics that contain a large fraction of oil. Most of these materials have low stiffness and poor oil-binding capacity at commercially viable concentrations, which limits their application in the food and cosmetic industries. To improve their mechanical behavior, we exploited the concepts of particulate-filled materials by developing oil-continuous monoglyceride composites reinforced with crystalline cellulose of various sizes. Cellulose was used as the reinforcing filler material due to its strength, biodegradability, and abundance. The composites gradually stiffened and became more brittle with a progressive increase of the cellulose weight fraction as the maximum packing fraction of fillers approached. This was manifested as an increase in the viscoelastic moduli and yield stress, consistent with the size of the filler. Based on differential scanning calorimetry, X-ray diffraction, X-ray scattering analyses, and microscopic analyses, the inert surface of crystalline celluloses provided a solid substrate for the crystallization of monoglycerides, favoring the lamellar stacking of monoglyceride molecules during the composite oleogel formation regardless of the cellulose size. The present study suggests that cellulose is a suitable bio-based filler material to obtain mechanically strong oleogels suitable for high-shear applications e.g., in food and pharmaceutical industries.

Influence of Hydrogen Bonds and π–π Interactions on the Fluorescence of Crystalline (N-Alkylpyridyl)enamino-pyrrolo[2,3-b]quinoxalin-2-one Derivatives

This paper presents the relationship between the fluorescent properties of (E/Z)-(N-alkylpyridyl)enamino-pyrrolo[2,3-b]quinoxalin-2-one derivatives in the crystalline state and the molecular packing governed by the conformation of the molecules, hydrogen bonding, and π–π interactions. In particular, the type of 2-pyridyl alkyl chain (2-Py(CH2)n with n = 0,1,2) is responsible for the molecular packing and influences the fluorescence properties of crystalline pyrrolo[2,3-b]quinoxalines. The molecules studied exhibit permanent dipole moments that, in the crystalline phases, promote either the formation of dimers with an antiparallel orientation or stacks with a parallel dipole moment orientation. In dimers and stacks, the main observed interaction is the π–π type. The conformations of both (E)- and (Z)-enamines are stabilized by intramolecular hydrogen bonds from the NH group of the enamine to either the nitrogen atom N4 of the quinoxaline (E)-diastereoisomer or the oxygen atom of the amide carbonyl group in the (Z)-diastereoisomer. When an additional intramolecular hydrogen bond from the enamine NH group to the pyridyl nitrogen atom forms, it affects the conformation of the molecules, causing the reorientation of the molecular permanent dipole moment. Density functional theory (DFT) calculations performed for two neighboring molecules in dimers or stacks indicate two charge transfer mechanisms: intra- and intermolecular mechanisms. For centrosymmetric dimers, charge transfer occurs within each component molecule (intramolecular charge transfer). For stacks with molecules arranged by translation and noncentrosymmetric dimers, charge transfer is of an intermolecular nature. Higher absolute fluorescence quantum yields (Φf = 12.06–13.77%) are exhibited by the (E-diastereoisomers, which contain methylene or ethylene chains and form either translational stacks of the molecules or noncentrosymmetric dimers. The lowest absolute fluorescence quantum yields (Φf = 3.80–4.00%) are typical for the centrosymmetric dimers present in crystalline (Z)-(N-pyridyl)enaminopyrrolo[2,3-b]quinoxaline and (E)-(N-ethylpyridyl)enamino-pyrrolo[2,3-b]quinoxaline. The fluorescence liftimes τ were determined for single crystals of the studied phases (from 13.3 to 15.6 ns) and revealed one single process of radiative energy transfer.

Lone pair/π-hole interactions in the edge-to-face stacking of the criss-cross construction molecule: Towards thermally stability, low sensitivity, and high detonation performance

4-Azasydnone-3,5-dinitropyrazole was synthesized and fully characterized by IR, multinuclear NMR spectroscopy, elemental analysis and differential scanning calorimetry (DSC). Its crystal structure was determined by single-crystal X-ray diffraction and packing characteristics were thoroughly studied by non-covalent interaction (NCI) and Hirshfeld surface analysis. The theoretical detonation pressure (P) and velocity (vD) were also calculated (Gaussian 09 and EXPLO5). Attributing to the lone pair/π-hole interactions in its dense edge-to-face packing structure, DNPA shows a high density (1.86 g cm−3), good thermal stability (Td = 229 °C), excellent detonation performance (vD = 8703 m s−1, P = 32.7 GPa) and acceptable sensitivities (IS = 17 J, FS = 230 N), and is deservedly superior to 1,3,5-trinitro-1,3,5-triazinane (RDX). These advantages highlight the potential use of DNPA as high-energy–density materials.

Enhanced chromonic stacking assisted by a hydrogel network

We report that the stacking order in lyotropic chromonic liquid crystal (LCLC) Sunset Yellow FCF (SSY) is enhanced when incorporated into a cationic hydrogel via the ionic bonds. The chromonic-incorporated gel is initially opaque but transparent and shows a birefringence at high temperatures. The stacking correlation length at room temperature (≈25 °C) is as large as 5.97 nm, corresponding to about 18 molecules in a single stack, and the stacking energy is found to be 7.96 k B T. Both values are larger than those in a normal SSY solution with the respective concentration (≈1 M).

Synthesis of novel acrylic liquid-crystal resin and its in-situ enhancement in light-curing 3D printing performance

Acrylic liquid-crystal resin (ALCR) was synthesized in three steps using 4-hydroxybenzoate 4-carboxylic phenyl ester as the mesocrystalline unit. The structure, heat resistance, and liquid–crystal properties of the ALCR were systematically investigated. The ALCR was used to produce new 3D printing inks, which exhibited good fluidity and rapid photopolymerization ability to meet the rheological prerequisites of 3D printing ink. Compared with commercial ink, the initial decomposition temperature increased from 304.9 to 334.3 °C, the glass transition temperature increased from 74.8 to 89.8 °C, and the storage modulus increased from 1107.6 to 2230.6 MPa for the ALCR inks. The tensile strength, elongation at break, flexural strength, impact strength, and hardness of an ink containing 20% ALCR were improved to 65.3 MPa, 17.3%, 103.9 MPa, 4.8 kJ m−2, and 77.1 HD, respectively, corresponding to 147.4%, 174.7%, 207.4%, 171.4%, and 106.6% of the values for commercial ink. These results indicate that ALCR can effectively improve the mechanical properties of 3D-printed products in-situ. This is because the liquid-crystal molecules in the product stack to form mesogenic domains. When subjected to an external force, these mesogenic domains exploit their own orientation, cross-linking, and high-strength characteristics to effectively improve the mechanical properties of the product.

Slot‐Die‐Coated Organic Solar Cells Optimized through Multistep Crystallization Kinetics

To fabricate organic solar cells (OSCs) via slot‐die coating, solvent additives are essential to induce an optimized phase‐separated and order morphology. It is critical to determine the morphological evolution from solution to solid state and understand the crystallization kinetics in slot‐die coating. Using in situ grazing‐incidence wide‐angle X‐ray scattering characterization, the morphological evolution in PM6‐ and ITIC‐based systems without or with 0.3% 1,8‐diiodooctane (DIO) as additive can be monitored in real‐time during slot‐die coating. As a result, DIO weakens the planarization of the PM6 backbone and splits the backbone ordering into fragments to form ordered crystallites. DIO also induces surface crystallization to reinforce the tie‐chain connections between the crystallites. Furthermore, in the ITIC system, DIO triggers the formation of an interconnected fibril network morphology and concurrently promotes the stacking of ITIC molecules in between the polymer network. Thus, an optimized morphology with a refined crystal structure is formed with the help of DIO. As a result, the power conversion efficiency is improved from 8.77% to 9.59% in slot‐die‐coated OSCs. These findings provide guidelines for optimizing the morphology in slot‐die‐coated OSCs and accelerate the transition of laboratory‐scale fabrication to industrial production.

Studies on Ni–SnO2 Nanocomposites for Humidity Sensing Application

AbstractWe report a hydrothermal method for synthesis of nickel‐doped tin oxide (Ni–SnO2) nanoparticles. The samples are characterized by different analysis techniques to understand their structural, morphological, and optical properties. The synthesized nanomaterials are characterized by X‐ray diffraction, it is crystallized in a tetragonal rutile crystal structure and the crystallite size increases from ∼5 to ∼23 nm with the increasing nickel (Ni) doping concentration. The field emission electron microscopy demonstrates that in case of doping the addition of polyethylene glycol is responsible for the development of densely packed flower like bunches. Further, the synthesized n‐type SnO2 materials are systematically investigated for humidity sensing toward atmospheric moisture. The results indicate that nickel doping improves the performance of SnO2 sensor and is highly sensitive over a wide relative humidity (%RH) range from 10% to 100% at room temperature than pure SnO2. It is found that the resistance of the films decreases with increasing RH as the multilayer stacking of water molecules occurred on the surface of synthesized nanomaterials. Also, the fast response time of 15 s and recovery time of 4 s are observed for the 5% nickel‐doped SnO2 sensor. This improved sensing performance is attributed to nickel doping as doping developed the proportions of oxygen vacancy and improves the large surface to volume ratio as well as exhibited high conductivity. Thus, the doping of SnO2 nanoparticles with Ni should be a promising approach for designing and fabricating the high‐performance humidity sensor.

Regulating phase separation and molecular stacking by introducing siloxane to small-molecule donors enables high efficiency all-small-molecule organic solar cells

Siloxane with low surface tension can regulate the intermolecular interactions, and optimize the phase separation morphology and molecule stacking, finally contributing to an excellent PCE of 16.4% with small energy loss for ASM-OSCs.