Columnar Stacks Research Articles

Nanographene Metallaprisms: Structure, Stimulated Transformation, and Emission Enhancement

AbstractNanographenes are inclined to assemble into stacked columnar structures that are stabilized by π‐π interactions, whereas other supramolecular structures of nanographenes, such as prisms and cages, are rarely investigated. Herein, a diazananographene was synthesized, and then assembled with a coordination unit, thereby producing a triangular metallaprism. After adding C60 or C70, the triangular metallaprism was transformed into a square tetramer, which encapsulated a pair of C60 or C70 molecules. The formed host‐guest complex demonstrated efficient energy transfer from the diazananographene shell to the C60 cores. The emission intensity of the capsulated C60 was enhanced remarkably, compared with free C60, due to an increased quantum yield and optical absorption coefficient. This work demonstrates the versatility of nanographene‐based supramolecular architectures beyond columnar stacking and their ability to enhance the emission of otherwise non‐emissive fullerene.

The Crystalline Behavior and Device Function of Nonfullerene Acceptors in Organic Solar Cells

AbstractThe current research investigates the structure features and intermolecular interactions of nonfullerene acceptors (NFAs) in single crystal and thin films, as well as their solar cell applications. Guiding parameters and key intermolecular forces that lead to 2D brickwork or 3D web packing are identified. The atomic modification is shown as the key to induce hydrogen bonding or π–π stacking column, which results in different crystalline packing. The molecular assembly in thin film is initiated by hydrogen bonding, and completed by π–π stacking reorganization. The packing energy is seen as a guiding parameter that dictates the NFA crystalline morphology in blended thin films. The crystalline packing motif is not directly related with device efficiency. However, the crystalline morphology is the key parameter to influence exciton/carrier dynamics and device performance. A broader picture on the scaling behavior of organic semiconductor crystals ranging from oligoacenes to NFAs is established.

Chiral Self-Recognition and Self-Discrimination Processes in Different Subphthalocyanine Aggregation Regimes

We have recently shown that, as a result of its rigid cone-shaped structure, racemic SubPcs trisubstituted with peripheral amides can self-assemble in two distinct regimes as a function of the solvent environment.1 In toluene, an apolar aromatic medium that can efficiently solvate p-surfaces, such compounds associate as tail-to-tail dimers (regime A). In methylcyclohexane (MCH), in contrast, they undergo a cooperative supramolecular polymerization process to yield non-centrosymmetric head-to-tail columnar stacks (regime B).2 SubPcs, being intrinsically chiral molecule, constitutes an ideal probe to study chiral self-sorting processes, which is the objective of this work. As depicted in the figure below, a racemic mixture of a trisubstituted SubPc can in principle self-assemble into different species. Homochiral dimers/polymers may form through a chiral self-recognition process: each enantiomer has a preference to aggregate with itself leading to helical supramolecular structures with a preferred handedness. At the other extreme, heterochiral dimers/polymers would be instead formed via a chiral self-discrimination process, where each enantiomer prefers to associate with the other, yielding purely racemic dimers/polymers displaying no predilection for a given helical sense. As an intermediate case, the enantiomers might show no strong self-sorting preference and yield statistical dimers/polymers.[1] C. G. Claessens, D. González-Rodríguez, M. S. Rodríguez-Morgade, A. Medina, T. Torres, Chem. Rev. 2014, 114, 2192.[2] (a) J. Calbo, J. Aragó, P. M. Viruela, E. Ortí, T. Torres, D. González-Rodríguez, Angew. Chem. Int. Ed. 2015, 54, 2543; (b) M. J. Mayoral, J. Guilleme, J. Calbo, J. Aragó, F. Aparicio, E. Ortí, T. Torres, D. González-Rodríguez, J. Am. Chem. Soc. 2020 , 142, 21017. Figure 1

Semi-flexible star-shaped molecules: conformational analysis of nano-segregated mesogens forming columnar liquid-crystal phases

Abstract The structural prerequisites are investigated, which make star-shaped molecules suitable precursors for the formation of columnar liquid-crystalline phases. Electronic structure calculations on smaller mesogens show that not all conformers exhibit the atomistic structure, the stability against distortion, and additional dipole moments, which favour columnar stacking. For the presently studied compounds with short terminating alkyl chains, the calculations indicate that the steric factor becomes dominant with increasing star size. Thus, the optimised geometric structures were employed to generate a simplified mathematical model of the structures, which accounts only for the steric interaction in the larger stars. With the help of these diagrams, the most common conformers of star-shaped molecules can be derived in a systematic fashion.

Thermodynamic equilibrium analysis on the dehydration of glycerol with monohydric alcohols to alkyl glyceryl ethers

AbstractUnder the conditions of the feed of 400 moles of alcohol + 100 moles of glycerol, 313–573 K and 0.1 MPa, based on Gibbs free energy global minimization, an improved genetic algorithm was used for the thermodynamic equilibrium analysis on the synthesis processes of alkyl glyceryl ethers, respectively, from methanol + glycerol, ethanol + glycerol, isobutanol + glycerol, and tert‐butanol + glycerol. The columnar stacking charts and three‐dimensional contour graphs were used to compare the effects of temperature, pressure, and the feed ratio to the equilibrium conversion, product selectivity, and equilibrium composition. The basic laws of the synthesis processes of alkyl glycerol ethers in homogeneous and heterogeneous states were investigated in a wide temperature range. Through comparison, it was found that the isopropanol + glycerol system is easier to convert into alkyl glycerol ethers, followed by the ethanol + glycerol system. The methanol + glycerol system and tert‐butanol + glycerol system are greatly affected by pressure and temperature, and their conversions and selectivities are relatively low.

Synthesis and crystal structure of a sulphur-bridged molecular hoop consisting of 5,7,12,14-tetrathiapentacene.

A cyclic dimer consisting of 5,7,12,14-tetrathiapentacene (TC[2]TTP) forms a new extended series of thiacalix[n]arenes, and was successfully synthesized by an intramolecular Friedel–Crafts-type condensation of the macrocyclic precursor. TC[2]TTP was characterized using 1H and 13C nuclear magnetic resonance and high-resolution mass spectrometry. Its hoop-shaped molecular structure was determined by X-ray crystallography. The two-tub-shaped TTP formed a hexagonal geometry via a sulphur linker, and TC[2]TTP adopted a honeycomb structure with columnar stacking in the crystal structure. Furthermore, TC[2]TTP exhibited crystal polymorphism, which incorporated appropriate organic solvents such as CHCl3, benzene, and toluene into its internal cavity. This suggests that TC[2]TTP is a candidate for the components of cavity-assembled porous solids based on molecular tiling.

Dielectric response of 1,1-difluorosumanene caused by an in-plane motion

A large dipole moment of 1,1-difluorosumanene realized a 120° in-plane pendulum motion in the stacking columns at above 380 K. This dynamic motion in the solid state enabled anisotropic dielectric relaxation induced by the external electric field.

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars.

This computational study investigates the influence of light on supramolecular aggregates of three-arm azobenzene stars. Every star contains three azobenzene (azo) moieties, each able to undergo reversible photoisomerization. In solution, the azo stars build column-shaped supramolecular aggregates. Previous experimental works report severe morphological changes of these aggregates under UV–Vis light. However, the underlying molecular mechanisms are still debated. Here we aim to elucidate how light affects the structure and stability of the columnar stacks on the molecular scale. The system is investigated using fully atomistic molecular dynamics (MD) simulations. To implement the effects of light, we first developed a stochastic model of the cyclic photoisomerization of azobenzene. This model reproduces the collective photoisomerization kinetics of the azo stars in good agreement with theory and previous experiments. We then apply light of various intensities and wavelengths on an equilibrated columnar stack of azo stars in water. The simulations indicate that the aggregate does not break into separate fragments upon light irradiation. Instead, the stack develops defects in the form of molecular shifts and reorientations and, as a result, it eventually loses its columnar shape. The mechanism and driving forces behind this order–disorder structural transition are clarified based on the simulations. In the end, we provide a new interpretation of the experimentally observed morphological changes.

Columnar Aggregates of Azobenzene Stars: Exploring Intermolecular Interactions, Structure, and Stability in Atomistic Simulations.

We present a simulation study of supramolecular aggregates formed by three-arm azobenzene (Azo) stars with a benzene-1,3,5-tricarboxamide (BTA) core in water. Previous experimental works by other research groups demonstrate that such Azo stars assemble into needle-like structures with light-responsive properties. Disregarding the response to light, we intend to characterize the equilibrium state of this system on the molecular scale. In particular, we aim to develop a thorough understanding of the binding mechanism between the molecules and analyze the structural properties of columnar stacks of Azo stars. Our study employs fully atomistic molecular dynamics (MD) simulations to model pre-assembled aggregates with various sizes and arrangements in water. In our detailed approach, we decompose the binding energies of the aggregates into the contributions due to the different types of non-covalent interactions and the contributions of the functional groups in the Azo stars. Initially, we investigate the origin and strength of the non-covalent interactions within a stacked dimer. Based on these findings, three arrangements of longer columnar stacks are prepared and equilibrated. We confirm that the binding energies of the stacks are mainly composed of – interactions between the conjugated parts of the molecules and hydrogen bonds formed between the stacked BTA cores. Our study quantifies the strength of these interactions and shows that the – interactions, especially between the Azo moieties, dominate the binding energies. We clarify that hydrogen bonds, which are predominant in BTA stacks, have only secondary energetic contributions in stacks of Azo stars but remain necessary stabilizers. Both types of interactions, – stacking and H-bonds, are required to maintain the columnar arrangement of the aggregates.

Enantiopure C5 Pentaindenocorannulenes: Chiral Graphenoid Materials.

Chiral carbon nanomaterials offer numerous prospects for material science. As a fundamental building block for non-planar graphenoid materials, pentaindenocorannulene (PIC) with its C5v symmetrical structure presents a platform for creation of supramolecular chiral carbon materials. Specifically, when uniformly penta-substituted on its periphery, PIC generates C5 symmetrical chiral buckybowls capable of columnar stacking. The synthesis and resolution of such PICs are achieved, assignment of absolute configuration is established by comparison of ECD and VCD spectra with theory, and material characterization is reported. Evidence for columnar stacking in solution and in the crystal is presented.

Enantiopure C5 Pentaindenocorannulenes: Chiral Graphenoid Materials

AbstractChiral carbon nanomaterials offer numerous prospects for material science. As a fundamental building block for non‐planar graphenoid materials, pentaindenocorannulene (PIC) with its C5v symmetrical structure presents a platform for creation of supramolecular chiral carbon materials. Specifically, when uniformly penta‐substituted on its periphery, PIC generates C5 symmetrical chiral buckybowls capable of columnar stacking. The synthesis and resolution of such PICs are achieved, assignment of absolute configuration is established by comparison of ECD and VCD spectra with theory, and material characterization is reported. Evidence for columnar stacking in solution and in the crystal is presented.

Solvophobicity-directed assembly of microporous molecular crystals

Dense packing is a universal tendency of organic molecules in the solid state. Typical porous crystals utilize reticular strong intermolecular bonding networks to overcome this principle. Here, we report a solvophobicity-based methodology for assembling discrete molecules into a porous form and succeed in synthesizing isostructural porous polymorphs of an amphiphilic aromatic molecule Py6Mes. A computational analysis of the crystal structure reveals the major contribution of dispersion interaction as the driving force for assembling Py6Mes into a columnar stacking while the columns are sterically salient and form nanopores between them. The porous packing is facilitated particularly in solvents with weak dispersion interaction due to the solvophobic effect. Conversely, solvents with strong dispersion interaction intercalate between Py6Mes due to the solvophilic effect and provide non-porous inclusion crystals. The solvophobicity-directed polymorphism is further corroborated by the polymorphs of Py6Mes-analogues, m-Py6Mes and Ph6Mes.

Asphaltenes as novel thermal conductivity enhancers for liquid paraffin: Insight from in silico modeling

The practical use of paraffin and other organic phase-change materials for heat storage is largely limited by their low thermal conductivity. In this paper we employed 60 microsecond-long atomic-scale computer simulations to explore for the first time whether the asphaltenes, natural polycyclic aromatic hydrocarbons, can be used as thermal conductivity enhancers for paraffin. We focused on a simple model molecule of asphaltene (a polycyclic aromatic core decorated with the peripheral alkane chains) and showed that the asphaltenes of such molecular architecture are not able to improve the thermal conductivity of paraffin. This is most likely due to the steric constraints imposed by the peripheral alkane groups, which prevent formation of the extended ordered asphaltene aggregates. To overcome this, we proposed a possible chemical modification of the asphaltene molecules through removing the peripheral alkane groups from their aromatic cores; this could be achieved e.g. by thermal cracking (dealkylation) of asphaltenes. It turns out that such a chemical modification drastically changes the situation: the modified asphaltenes form extended columnar aggregates which can serve as thermal conduction paths, considerably enhancing the thermal conductivity of a liquid composite sample. This effect, however, vanishes upon cooling because the columnar extended stacks of chemically modified asphaltenes transform into the helical twisted structures, which reduces the overlap of adjacent asphaltenes in aggregates. Importantly, all the simulations have been carried out with two different all-atom force fields. We have demonstrated that both computational models give qualitatively similar results. Overall, our findings clearly show that chemically modified asphaltene molecules can be considered as promising carbon-based thermal conductivity enhancers for liquid paraffin; this result can be used for optimizing the paraffin-based thermal energy storage systems.

Preparation of Liquid Crystalline Subnaphthalocyanines As Optoelectronic Materials

Chloroboron(III) hexachloro- hexabromo-, and hexaiodosubnaphthalocyanines were prepared by cyclotrimerization of 6,7-dihalo-2,3-naphthalenedicarbonitrile in the presence of BCl3, They were converted to fluoroboron(III) hexahalosubnaphthalocyanine by the reaction with AgBF4. Their solubility, electronic absorption spectroscopy, fluorescence emission spectroscopy and HOMO/LUMO energy levels were evaluated. Fluorescence quantum yields of chloroboron(III) hexafluoro-, hexachloro-, hexabromo-, and hexaiodosubnaphthalocyanine were 0.22, 0.20, 0.11, 0.05, respectively, indicating that heavy atom effects of Br and I were effectively deactivate the singlet excited states. These subnaphthalocyanines showed lower HOMO/LUMO energies than the parent subnaphthalocyanine by 0.13 – 0.39 eV. The optical band gap decreased in the order: hexafluoro- > hexachloro- > unsubstituted > hexaiodo-subnaphthalocyanine. Hexaiodosubnaphthalocyanines were converted to chloroboron(III) and fluoroboron(III) hexa(1-alkynyl)- and hexa(2-arylethynyl)subnaphthalo-cyanines by Sonogashira coupling of hexaiodosubnaphthalocyanines with substituted acetylenes. Introduction of butyl or longer alkyl groups via ethynylene linkages on the periphery resulted in lower melting points, and higher solubility in dichloromethane. X-ray diffraction (XRD) patterns of the cast film indicated that hexa(2-(4-hexylphenyl)ethynyl)- and hexa(2-(4-hexyloxyphenyl)ethynyl)subnaphthalocyanines with a B-F bond are packed in a discotic hexagonal columnar phase with lattice constants a = 59-64 Å and stacking distance c = 4.7-4.8 Å. The Q-band in visible spectra of the thin film of these B-F derivatives was blue-shifted, supporting the formation of H-aggregate in stacked columns. Polarized optical microscope showed that these subnaphthalocyanines with a B-F bond exhibited mesophase at 180oC. XRD of these subnaphthalocyanines at 180 oC confirms a two dimensional hexagonal phase. XRD of the corresponding derivatives with a B-Cl bond showed that they were either amorphous or less crystalline. Figure 1

Design and Calibration of a Hall Effect System for Measurement of Six-Degree-of-Freedom Motion within a Stacked Column.

This paper presents the design, development and evaluation of a unique non-contact instrumentation system that can accurately measure the interface displacement between two rigid components in six degrees of freedom. The system was developed to allow measurement of the relative displacements between interfaces within a stacked column of brick-like components, with an accuracy of 0.05 mm and 0.1 degrees. The columns comprised up to 14 components, with each component being a scale model of a graphite brick within an Advanced Gas-cooled Reactor core. A set of 585 of these columns makes up the Multi Layer Array, which was designed to investigate the response of the reactor core to seismic inputs, with excitation levels up to 1 g from 0 to 100 Hz. The nature of the application required a compact and robust design capable of accurately recording fully coupled motion in all six degrees of freedom during dynamic testing. The novel design implemented 12 Hall effect sensors with a calibration procedure based on system identification techniques. The measurement uncertainty was ±0.050 mm for displacement and ±0.052 degrees for rotation, and the system can tolerate loss of data from two sensors with the uncertainly increasing to only 0.061 mm in translation and 0.088 degrees in rotation. The system has been deployed in a research programme that has enabled EDF to present seismic safety cases to the Office for Nuclear Regulation, resulting in life extension approvals for several reactors. The measurement system developed could be readily applied to other situations where the imposed level of stress at the interface causes negligible material strain, and accurate non-contact six-degree-of-freedom interface measurement is required.

Synthesis, crystal structure, thermal analysis and magnetic properties of two bis(oxalato)cuprate(II) hybrid salts crystallizing with lattice oxalic acid molecules

Two novel bis(oxalato)cuprate(II) salts, (C7H11N2)2[Cu(C2O4)2]·H2C2O4 (1) and (C5H7N2)2[Cu(C2O4)2(H2O)2]·2H2C2O4 (2) {(C7H11N2)+ = 4-dimethylaminopyridinium, (C5H7N2)+ = 3-aminopyridinium} have been synthesized and characterized by elemental and thermal analyses, single-crystal X-ray diffraction, IR spectroscopy and SQUID magnetometry. Compounds 1 and 2 crystallize in the triclinic P-1 space group. The two structures differ in terms of the coordination ligands around the Cu(II) centers as well as the number of the lattice oxalic acid molecules. The crystal structure of 1 is made of columnar stacks of [Cu(C2O4)2]2- anions through axial Cu∙∙∙O contacts (2.89 Å), yielding straight Cu(II) chains with a prolate CuO6 octahedron around Cu(II) ions. In this chain structure, the intermetallic Cu∙∙∙Cu separation between two adjacent Cu(II) ions is 3.71 Å. The crystal structure of 2 is characterized by the [Cu(C2O4)2(H2O)2]2- complex anion in which aqua ligands are in trans-configuration, with the Cu(II) ion adopting a distorted (4 + 2) octahedral coordination. In the two compounds, the ionic components together with the lattice oxalic acid molecules are connected via intermolecular NH∙∙∙O and OH∙∙∙O hydrogen bonds into a three-dimensional network. In addition, π–π stacking interactions between pyridine rings contribute to the stabilization of the crystal packing. Temperature-dependence susceptibility measurements investigated in the temperature range 2–300 K revealed weak antiferromagnetic coupling at low temperatures in both compounds.

An n-Type Benzobisthiadiazole-Based Covalent Organic Framework with Narrowed Bandgap and Enhanced Electroactivity

Low-bandgap covalent organic frameworks (COFs) emerge as one of the most intriguing conjugated polymers for the development of electronic devices, while they often lack desirable electron affinity, thereby compromising the activity and stability in electrochemical transformation. Here, we report an n-type semiconducting two-dimensional (2D) COF, featuring a low bandgap (1.36 eV) and strong electron affinity (4.41 eV) as well as high crystallinity and porosity. The columnar stacking array of the benzobisthiadiazole moiety in 2D COFs plays a critical role in elevating electroactivity. It not only leads to the outstanding electrical conductivity and air stability upon reductive doping but also enables the boost of transformation kinetics for polysulfides on the separators of lithium–sulfur batteries causing a higher capacity and better cycling performance. The design strategy underpins the versatile development of electroactive COF materials with desirable electronic properties and promotes their applicability in energy storage and electronics.

A Molecular Transformer: A π‐Conjugated Macrocycle as an Adaptable Host

AbstractHere, we report a facile method to synthesize a series of macrocycles with different conformations. The planar macrocycle dimer (1), twisted macrocycle trimer (2) and “figure‐eight” tetramer (3) are clearly elucidated by X‐ray single‐crystal analysis, in which the electron‐rich phenanthrene units offer the possibility of supramolecular assembly. As expected, in the solid state, 1 and 3 assemble into a columnar stack and an interlocking dimer, respectively, via π–π interactions between the phenanthrene units. Compared to the rigid conformation of dimer 1, the structure of tetramer 3 is more flexible due to its enlarged ring size. 3 can deform from a figure‐eight into a boat‐shaped geometry to host a planar electron‐deficient guest using its electron‐rich phenanthrene units. When assembled with spherical electron‐deficient C60, interestingly, 3 further undergoes a conformational transformation from a figure‐eight to a belt shape in order to host C60. These supramolecular assembly behaviors of 3 demonstrate that it is an adaptable macrocyclic host for both planar molecules and fullerenes.

A Molecular Transformer: A π-Conjugated Macrocycle as an Adaptable Host.

Here, we report a facile method to synthesize a series of macrocycles with different conformations. The planar macrocycle dimer (1), twisted macrocycle trimer (2) and "figure-eight" tetramer (3) are clearly elucidated by X-ray single-crystal analysis, in which the electron-rich phenanthrene units offer the possibility of supramolecular assembly. As expected, in the solid state, 1 and 3 assemble into a columnar stack and an interlocking dimer, respectively, via π-π interactions between the phenanthrene units. Compared to the rigid conformation of dimer 1, the structure of tetramer 3 is more flexible due to its enlarged ring size. 3 can deform from a figure-eight into a boat-shaped geometry to host a planar electron-deficient guest using its electron-rich phenanthrene units. When assembled with spherical electron-deficient C60 , interestingly, 3 further undergoes a conformational transformation from a figure-eight to a belt shape in order to host C60 . These supramolecular assembly behaviors of 3 demonstrate that it is an adaptable macrocyclic host for both planar molecules and fullerenes.

Coexistence of Parallel and Rotary Stackings in the Lamellar Crystals of a Perylene Bisimide Dyad for Temperature-Sensitive Bicomponent Emission.

Coexistence of rotationally π-π stacked columns and discrete slip-stacked dimers of perylene bisimide (PBI) chromophores is revealed by single crystal X-ray diffraction in the lamellar crystal of a head-to-tail linked PBI dyad. The rotary π-π stacked columnar moieties show H-type spectral character with relatively higher excitation energy, while the discrete slip-stacked π-π dimers have J-type spectral behavior with lower excitation energy. The lamellar crystals show relatively low photoluminescence efficiency of 12% at room temperature, while this dramatically increases to ∼90% at low temperature (80 K). Both of the rotary and slip-stacked moieties are emissive, and the nonradiative energy transfer processes between them are suppressed at low temperature, ensuring the highly efficient excimer-like long-lived fluorescence.