Packing Arrangement Research Articles

Optical nature of non‐substituted triphenylmethyl cation: Crystalline state emission, thermochromism, and phosphorescence

AbstractSince the discovery of the triphenylmethyl (trityl) cation 120 years ago, a variety of aromatic cations having various colors and luminescence properties have been rigorously studied. Many, differently substituted trityl cations have been synthesized, and their optical properties have been elucidated. However, the optical properties of the parent, non‐substituted and highly reactive trityl cation, which was observed to be very weakly luminescent, have not been subjected to detailed investigation. In the effort described herein, we explored the optical nature of non‐substituted trityl hexafluorophosphate (PF6) in the crystalline state. Trityl PF6 was found to exist as two crystal polymorphs including a yellow (Y) and an orange (O) form. Moreover, we observed that these crystalline forms display crystalline‐state emission with different colors. The results of X‐ray crystallographic analysis showed that the two polymorphs have totally different molecular packing arrangements. Furthermore, an investigation of their optical properties revealed that the O‐crystal undergoes a distinct color change to yellow upon cooling as a consequence of a change in the nature of the charge transfer interaction between the cation and PF6 anion, and that both the Y‐ and O‐crystal exhibit phosphorescence.

CFD Investigation of helium gas flow in sphere packed (Pebble bed) in a rectangular canister using OpenFOAM

The lead-lithium cooled ceramic breeder uses spherical lithium titanate pebbles, which act as the breeder for generating tritium as the fuel for nuclear fusion reaction and helium as the purging gas. In this work, the flow-field of helium gas and temperature distribution inside a rectangular canister is investigated numerically, considering the pebble bed as the porous medium. In the numerical model, the local thermal non-equilibrium (LTNE) is assumed to exist between the pebbles and the purging gas, and a local porosity distribution is considered. Considering the radiation effect, a heterogeneous and LTNE based solver developed in OpenFOAM software is validated with the published results. Further, the effects of different heat generation rates, mass flow rates, and packing arrangements (random and uniform arrangements, i.e. BCC and FCC) on the flow-field and temperature profile are studied. The BCC and FCC packing arrangements have better purging behaviour than random packing. Further, the effect of inlet and outlet configuration is evaluated to find the optimal locations for uniform distributions of purging gas in the canister. With a higher value of area-weighted average velocity, the diagonally opposite inlet-outlet is the best choice for removing tritium from the packed bed.

The impact of the molecular structure on aggregation and solid state luminescence of 2,3-diarylfumaronitriles

This work focuses on the substituent effect in 2,3-diarylfumaronitriles on the optical properties and intermolecular interactions in the solid state. 2,3-Diarylfumaronitriles show various luminescence behaviour in solution and in the solid state. Aggregation patterns of 2,3-diarylfumaronitriles govern their luminescent properties in the solid state. The weak intermolecular interactions NC···NC, C–H···Cl, and C–H···NC were detected in the X-ray structures of 2,3-diarylfumaronitriles and studied by DFT calculations at the M06–2X/6–311++G(d,p) level of theory and topological analysis of the electron density distribution within the framework of QTAIM method. The estimated strength of these non-covalent bonds is 0.8–1.3 kcal/mol. The orientation of molecules in crystals depends on the substituents in 2,3-diarylfumaronitriles. Distinct molecular orientation and packing arrangements in crystalline 2,3-diarylfumaronitriles ensured perturbed electronic communication amongst the nearest and non-nearest molecules through an interplay of excimer and dipole couplings. As a result, the intermolecular interactions govern the solid state luminescence of molecules.

Crystal structures of three N-(pyridine-2-carbon-yl)pyridine-2-carboxamides as potential ligands for supra-molecular chemistry.

The synthesis and single-crystal X-ray structures of three N-(pyridine-2-carbon-yl)pyridine-2-carboxamide imides, with or without F atoms on the 3-position of the pyridine rings are reported, namely, N-(pyridine-2-carbon-yl)pyridine-2-carboxamide, C12H9N3O2 (1), N-(3-fluoro-pyridine-2-carbon-yl)pyridine-2-carboxamide, C12H8FN3O2 (2), and 3-fluoro-N-(3-fluoro-pyridine-2-carbon-yl)pyridine-2-carboxamide, C12H7F2N3O2 (3). The above-mentioned compounds were synthesized by a mild, general procedure with an excellent yield, providing straightforward access to symmetrical and/or asymmetrical heterocyclic ureas. The crystal structures of 1 and 2 are isomorphous, showing similar packing arrangements, i.e. double layers of parallel (face-to-face) mol-ecules alternating with analogous, but perpendicularly oriented, double layers. In contrast, the crystal structure of 3, containing a fluoro- group at the 3-position of both pyridine rings, shows mol-ecular arrangements in a longitudinal, tubular manner along the c axis, with the aromatic pyridine and carbon-yl/fluorine moieties facing towards each other.

The Polymorphism of 2-Benzoyl-N,N-diethylbenzamide

The crystal structures of two new polymorphs of 2-benzoyl-N,N-diethylbenzamide were obtained after recrystallization trials with different solvents. The new forms II and III were monoclinic and crystallized in the same space group with similar a, b and c lengths but different β angles. The forms had no conformation differences within themselves; however, the long-range packing (>two unit cells) was not isostructural. In comparison with the previously published crystal structure, form I, different conformations and packing arrangements were observed. The new form II was thermally characterized and stable at room temperature, when heated up to its melting point and when cooled to −170 °C. Additionally, once form II was re-heated, a fourth form is observed after a phase transition from the monoclinic to the orthorhombic crystal systems, form IV.

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Computational Screening of Chiral Organic Semiconductors: Exploring Side-Group Functionalization and Assembly to Optimize Charge Transport

Molecular materials are challenging to design as their packing arrangements, and hence their properties, are subject to subtle variations in the interplay of soft intermolecular interactions. Rational design of new molecular materials with tailored properties is currently hampered by the difficulty in predicting how a candidate molecule will pack in space and how to control the particular polymorph obtained experimentally. Here, we develop a rapid screening approach to aid the material design process, which is then applied to predict the charge-transfer properties of 1344 helicene compounds that have potential as organic electronic materials. Our approach bridges the gap between single-molecule design, molecular assembly, and the resulting charge-carrier mobilities. We find that fluorination significantly improves electron transport in the molecular material by over 200%, while side groups containing triple bonds largely lead to improved transfer integrals. We validate our screening approach through the use of full crystal structure prediction for the most promising compounds to confirm the presence of favorable packing motifs that maximize charge mobility.

V-shaped triazine host featuring intramolecular non-covalent interaction for highly efficient white electroluminescent devices

The exploration of host materials with simultaneously excellent electrical properties and high triplet energy levels is highly essential but challenging in the fields of blue and white phosphorescence (Ph) and thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Herein, the symmetric V-shaped triazine host of DCzT in D-A-D molecular configuration featuring non-covalent intramolecular interactions (NCIs) was designed and synthesized through the replacement of phenyl core of highly twisted blue host of mCP by the acceptor unit of 2,4-dichloro-1,3,5-triazine. By means of the NCIs, DCzT demonstrates a relatively closed plane, thus boosting ordered molecular packing arrangement for the formation of carrier transport channel to acquire enhanced and balanced electrical performance at a high triplet energy level. Excitingly, highly efficient white TADF OLEDs was achieved displaying maximum luminance of 12000 cd m−2 and external quantum, current and power efficiencies of 23.2%, 66.9 cd A-1 and 70.0 lm W−1, respectively. This work highlights that the NCI affords a simple and intelligent way to regulate the electrical attributes of organic optoelectronic materials.

Two Crystal Forms of a Hydrated 2:1 β-Cyclodextrin Fluconazole Complex: Single Crystal X-ray Structures, Dehydration Profiles, and Conditions for Their Individual Isolation

Inclusion complexes between cyclodextrins (CDs) and active pharmaceutical ingredients (APIs) have potential for pharmaceutical formulation. Since crystallization of a given complex may result in the isolation of multiple crystal forms, it is essential to characterize these forms with respect to their structures and physicochemical properties to optimize pharmaceutical candidate selection. Here, we report the preparation and characterization of two crystallographically distinct hydrated forms of an inclusion complex between β-cyclodextrin (β-CD) and the antifungal API fluconazole (FLU) as well as temperature–concentration conditions required for their individual isolation. Determination of crystal water contents was achieved using thermoanalytical methods. X-ray analyses revealed distinct structural differences between the triclinic (TBCDFLU, space group P1) and monoclinic (MBCDFLU, space group C2) crystal forms. Removal of the crystals from their mother liquors led to rapid dehydration of the MBCDFLU crystal, while the TBCDFLU crystal was stable, a result that could be reconciled with the distinct packing arrangements in the respective crystals. This study highlights (a) the importance of identifying possible multiple forms of a cyclodextrin API complex and controlling the crystallization conditions, and (b) the need to characterize such crystal forms to determine the extent to which their physicochemical properties may differ.

Analyzing Hydration Differences in Cocrystal Polymorphs: High-Resolution X-ray Investigation of Caffeine–Glutaric Acid Cocrystals

Two polymorphic forms of caffeine (CAF)–glutaric acid (GLU) cocrystals have been studied via high-resolution X-ray crystallography and Bader’s quantum theory of atoms in molecules (QTAIM). For both the monoclinic, 1, and triclinic, 2, systems the experimental charge density distributions of the 1:1 ratio of CAF and GLU polymorphs have been determined and compared. Previous studies have determined that 1 is less stable than 2, in relative humidity (RH) testing. A topological analysis of the electron density distribution (EDD) revealed little difference between the two polymorph internal systems. The packing densities (0.76 vs 0.74) and lattice energies (−101.1 vs −107.1 kJ mol–1) of 1 and 2, respectively, are nearly equivalent, implying that the differences in hygroscopicity between the two polymorphs are not due to crystal lattice porosity or stability. A topological analysis of the number and strength of hydrogen bonds for 1 and 2 revealed nine hydrogen bonds in both polymorphs. “Classical” (O–H···X) hydrogen bonds were similarly present in both polymorphs, stabilizing the cocrystals. However, the sum of the stability produced from the “nonclassical” (C–H···X) bonds is higher in 2: −27.6 vs −38.2 kJ mol–1 for 1 and 2, respectively. One of the nine hydrogen bonds in 1 and 2 varies from the others, caused by the torsional rotation of the aliphatic carbon chain in GLU. This bond is critical for packing stabilization, creating a parallelogram-like packing arrangement in 2 in comparison to ribboning in 1. A Hirshfeld surface analysis found that the percentages of O–H···X hydrogen bonds were nearly identical in 1 and 2 (23.9% vs 22.1%); however, the H···H contacts were higher in 2 (61.4% vs 65.8% for 1 and 2, respectively), suggesting that more hydrogen-based contacts require competitive displacement by water in the hydration of 2 in comparison to 1. Additionally, a stabilizing aromatic cycle stack between CAF molecules is present in 2 due to the varied parallelogram packing arrangement, which was absent in 1; this provided ∼11.3 kJ mol–1 of stability to the system of 2. The solid-state entropies and molecular dipole moments (MDMs) of 1 and 2 supported the relative stability of the individual polymorphs, with 1 having a higher entropy and dipole moment in comparison to 2 (123.2 vs 112.8 J K–1 mol–1 and 7.45 and 4.93 D for 1 and 2, respectively), implying that it has the potential to hydrate more rapidly. These findings are in good agreement with previous experimental RH stability studies, giving further insight into the information gained from thermally averaged ground-state crystal electron density data.

Y-shaped AIEE active quinoxaline-benzothiazole conjugate for fluorimetric sensing of nitroaromatics in aqueous media

Three novel Y-shaped dimer quadrupolar A(-D-A)2 derivatives with quinoxaline and benzothiazole rings as the acceptors and biphenyl ring as the donor were synthesized in good yields by simple condensation reaction. Twisted structure along with herringbone packing arrangement for QB1 was depicted by single crystal X-ray diffraction studies. Aggregation induced emission enhancement (AIEE) was exhibited by all in THF-Water mixture. Naked eye colour change from colourless to yellow upon addition of picric acid accompanied with quenching of emission intensity was observed for all in aqueous as well as in THF solution. Detection limits of the probes towards picric acid were found in the submicromolar range. Large spectral overlap between absorption spectra of picric acid and emission spectra of probes depicted energy transfer as plausible fluorescence quenching mechanism. Further, the 1:2 binding stoichiometry of the probes towards picric acid was determined by Job’s plot. Filter paper strips for picric acid sensing were also fabricated. These novel compounds were also able to detect volatile acids like trifluoroacetic acid (TFA).

Regulation of Thermally Activated Delayed Fluorescence to Room-Temperature Phosphorescent Emission Channels by Controlling the Excited-States Dynamics via J- and H-Aggregation.

Control of excited-state dynamics is key in tuning room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) emissions but is challenging for organic luminescent materials (OLMs). We show the regulation of TADF and RTP emissions of a boron difluoride β-acetylnaphthalene chelate (βCBF2 ) by controlling the excited-state dynamics via its J- and H-aggregation states. Two crystalline polymorphs emitting green and red light have been controllably obtained. Although both monoclinic, the green and red crystals are dominated by J- and H-aggregation, respectively, owing to different molecular packing arrangements. J-aggregation significantly reduces the energy gap between the lowest singlet and triplet excited states for ultra-fast reverse intersystem crossing (RISC) and enhances the radiative singlet decay, together leading to TADF. The H-aggregation accelerates the ISC and suppresses the radiative singlet decay, helping to stabilize the triplet exciton for RTP.

Regulation of Thermally Activated Delayed Fluorescence to Room‐Temperature Phosphorescent Emission Channels by Controlling the Excited‐States Dynamics via J‐ and H‐Aggregation

AbstractControl of excited‐state dynamics is key in tuning room‐temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) emissions but is challenging for organic luminescent materials (OLMs). We show the regulation of TADF and RTP emissions of a boron difluoride β‐acetylnaphthalene chelate (βCBF2) by controlling the excited‐state dynamics via its J‐ and H‐aggregation states. Two crystalline polymorphs emitting green and red light have been controllably obtained. Although both monoclinic, the green and red crystals are dominated by J‐ and H‐aggregation, respectively, owing to different molecular packing arrangements. J‐aggregation significantly reduces the energy gap between the lowest singlet and triplet excited states for ultra‐fast reverse intersystem crossing (RISC) and enhances the radiative singlet decay, together leading to TADF. The H‐aggregation accelerates the ISC and suppresses the radiative singlet decay, helping to stabilize the triplet exciton for RTP.

Optimizing the self‐assembly of conjugated polymers and small molecules through structurally programmed non‐covalent control

AbstractOrganic conjugated polymers and oligomers are key electronic materials for applications such as transistors, photovoltaics, and light emitting devices due to their potential for solution processability, mechanical flexibility, and precise structure‐based tuning compared to inorganic materials. In dilute environments, the optoelectronic properties of conjugated polymers are largely governed by their constitutional structure and, to a lesser degree, their solution‐state intramolecular configuration. In the solid state, intramolecular conformation and intermolecular electronic coupling impact these properties substantially, especially in relation to device performance. Therefore, an increasingly important area of research concerning conjugated materials is developing design strategies aimed at optimizing the solid‐state packing for electronic applications. Programming solid‐state packing arrangements through discrete non‐covalent interactions is an emerging strategy within the context of conjugated polymers. This review focuses on the use of the two most prevalent discrete and directional interactions used to dictate the self‐assembly of conjugated polymers and oligomers—hydrogen bonds and chalcogen bonds. We also discuss how these design motifs can imbue conjugated materials with appealing physical properties while simultaneously retaining or improving electronic capabilities.

Influence of Terminal Functionality on the Crystal Packing Behaviour and Cytotoxicity of Aromatic Oligoamides.

The synthesis and characterization of three aromatic oligoamides, constructed from the same pyridyl carboxamide core but incorporating distinct end groups of acetyl (Ac) 1, tert-butyloxycarbonyl (Boc) 2 and amine 3 is reported. Single crystal X-ray diffraction analysis of 1–3 and a dimethylsulfoxide (DMSO) solvate of 2 (2-DMSO), has identified the presence of a range of intra- and intermolecular interactions including N-H⋯N, N-H⋯O=C and N-H⋯O=S(CH3)2 hydrogen-bonding interactions, C-H⋯π interactions and off-set, face-to-face stacking π-π interactions that support the variety of slipped stack, herringbone and cofacial crystal packing arrangements observed in 1–3. Additionally, the cytotoxicity of this series of aromatic oligoamides was assessed against two human ovarian (A2780 and A2780cisR), two human breast (MCF-7 and MDA-MB-231) cancerous cell lines and one non-malignant human epithelial cell line (PNT-2), to investigate the influence of the terminal functionality of these aromatic oligoamides on their biological activity. The chemosensitivity results highlight that modification of the terminal group from Ac to Boc in 1 and 2 leads to a 3-fold increase in antiproliferative activity against the cisplatin-sensitive ovarian carcinoma cell line, A2780. The presence of the amine termini in 3 gave the only member of the series to display activity against the cisplatin-resistance ovarian carcinoma cell line, A2780cisR. Compound 2 is the lead candidate of this series, displaying high selectivity towards A2780 cancer cells when compared to non-malignant PNT-2 cells, with a selectivity index value >4.2. Importantly, this compound is more selective towards A2780 (cf. PNT-2) than the clinical platinum drugs oxaliplatin by > 2.6-fold and carboplatin by > 1.6-fold.

Disazo (Bishydrazone) pigments based on acetoacetanilides

AbstractDisazoacetoacetanilide pigments, more commonly known as diarylide yellows, are the most important group of yellow classical organic pigments. They were commercialized in the early 20th century many years after the introduction of the structurally related monazoacetoacetanilides (Hansa yellows). The molecules adopt the bis-ketohydrazone tautomeric form. X-ray single crystal structure investigations have provided an insight into the influence of the molecular geometry and crystal packing arrangements in the solid state on the properties of the pigments in application. The synthesis of diarylide pigments is relatively straightforward, the conditions essentially following those used for the corresponding monoazo pigments, so that the products are economically priced. In the case of these disazo pigments, suitable aromatic amines (1 mol) are bis-diazotized and the resulting bis-diazonium salts reacted with acetoacetanilide coupling components (2 mol), the two azo coupling reactions occurring at the same time. They are by far the dominant group of yellow pigments used in printing inks, well-suited for most standard process yellow inks. They were formerly important in the coloration of plastics but are no longer recommended for polymers processed above 200 °C, under which conditions toxic decomposition products are formed. Diarylide yellow pigments are characterized by high color strength, good to excellent solvent fastness, and good chemical stability, although they generally show inferior lightfastness.

Role of backbone strain in de novo design of complex \u03b1/\u03b2 protein structures

We previously elucidated principles for designing ideal proteins with completely consistent local and non-local interactions which have enabled the design of a wide range of new αβ-proteins with four or fewer β-strands. The principles relate local backbone structures to supersecondary-structure packing arrangements of α-helices and β-strands. Here, we test the generality of the principles by employing them to design larger proteins with five- and six- stranded β-sheets flanked by α-helices. The initial designs were monomeric in solution with high thermal stability, and the nuclear magnetic resonance (NMR) structure of one was close to the design model, but for two others the order of strands in the β-sheet was swapped. Investigation into the origins of this strand swapping suggested that the global structures of the design models were more strained than the NMR structures. We incorporated explicit consideration of global backbone strain into the design methodology, and succeeded in designing proteins with the intended unswapped strand arrangements. These results illustrate the value of experimental structure determination in guiding improvement of de novo design, and the importance of consistency between local, supersecondary, and global tertiary interactions in determining protein topology. The augmented set of principles should inform the design of larger functional proteins.

Green Stereoregular Polymerization of Poly(methyl methacrylate)s Through Vesicular Catalysis

Green Stereoregular Polymerization of Poly(methyl methacrylate)s Through Vesicular Catalysis

13.4 % Efficiency from All-Small-Molecule Organic Solar Cells Based on a Crystalline Donor with Chlorine and Trialkylsilyl Substitutions.

How to simultaneously achieve both high open‐circuit voltage (V oc) and high short‐circuit current density (J sc) is a big challenge for realising high power conversion efficiency (PCE) in all‐small‐molecule organic solar cells (all‐SM OSCs). Herein, a novel small molecule (SM)‐donor, namely FYSM−SiCl, with trialkylsilyl and chlorine substitutions was designed and synthesized. Compared to the original SM‐donor FYSM−H, FYSM−Si with trialkylsilyl substitution showed a decreased crystallinity and lower highest occupied molecular orbital (HOMO) level, while FYSM−SiCl had an improved crystallinity, more ordered packing arrangement, significantly lower HOMO level, and predominant “face‐on” orientation. Matched with a SM‐acceptor Y6, the FYSM−SiCl‐based all‐SM OSCs exhibited both high V oc of 0.85 V and high J sc of 23.7 mA cm−2, which is rare for all‐SM OSCs and could be attributed to the low HOMO level of FYSM−SiCl donor and the delicate balance between high crystallinity and suitable blend morphology. As a result, FYSM−SiCl achieved a high PCE of 13.4 % in all‐SM OSCs, which was much higher than those of the FYSM−H‐ (10.9 %) and FYSM−Si‐based devices (12.2 %). This work demonstrated a promising method for the design of efficient SM‐donors by a side‐chain engineering strategy via the introduction of trialkylsilyl and chlorine substitutions.

COMPACT: Concurrent or Ordered Matrix-Based Packing Arrangement Computation Technique

Despite their versatility in treating irregular geometries, the raster methods have received limited attention in solving packing problems involving rotatable objects. In addition, raster approximation allows the use of unique performance metrics and indirect consideration of constraints, which have not been exploited in the literature. This study presents the Concurrent or Ordered Matrix-based Packing Arrangement Computation Technique (COMPACT). The method allows the objects to be rotated by arbitrary angles, unlike the right-angled rotation restrictions imposed in many existing packing optimization studies based on raster methods. The raster approximations are obtained through loop-free operations that improve efficiency. Additionally, a novel performance metric is introduced, which favors efficient filling of the available space by maximizing the overall contact within the domain. Moreover, the objective functions are exploited to discard the overlap and overflow constraints and enable the use of unconstrained optimization methods. The results of the case studies demonstrate the effectiveness of the proposed technique.