Intermolecular Packing Research Articles

Triptycene-Based Molecular Rods for Langmuir-Blodgett Monolayers.

Herein we introduce fully modular synthesis leading to three representative examples of rigid molecular rods that are intended to form sturdy monolayers on various surfaces. These molecules contain two triptycene units that are designed to interlock into a compact "double-decker" structure. Two of the three final products provided suitable crystals for X-ray diffraction (analyzed on synchrotron), allowing deeper insight into packing in the 3-D crystal lattice. The acidity of all three compounds were determined by capillary electrophoresis, and the pKa values ranged between 2.06-2.53. All three rigid rods easily formed Langmuir-Blodgett monolayers (LBMs) on the water-air interfaces, with the area per molecule equal to 55-59 Å2 /molecule, suggesting tight intermolecular packing. The thickness of all three films reached ∼19 Å after transfer to a gold (111) surface, meaning that individual molecules are tilted maximally 38° from the axis perpendicular to the surface. The structure of one of these films on a gold (111) surface was visualized by AFM. These geometrically unique molecules represent promising platforms with a wide scope of applicability in the supramolecular architecture.

Crystal structures of 3-halo-2-organochalcogenylbenzo[b]chalcogenophenes.

The structure of the title compounds 3-bromo-2-(phenyl-sulfan-yl)benzo[b]thiophene (C14H9BrS2; 1), 3-iodo-2-(phenyl-sulfan-yl)benzo[b]thio-phene (C14H9IS2; 2), 3-bromo-2-(phenyl-selan-yl)benzo[b]seleno-phene (C14H9BrSe2; 3), and 3-iodo-2-(phenyl-selan-yl)benzo[b]seleno-phene (C14H9ISe2; 4) were determined by single-crystal X-ray diffraction; all structures presented monoclinic (P21/c) symmetry. The phenyl group is distant from the halogen atom to minimize the steric hindrance repulsion for all structures. Moreover, the structures of 3 and 4 show an almost linear alignment of halogen-selenium-carbon atoms arising from the intra-molecular orbital inter-action between a lone pair of electrons on the halogen atom and the anti-bonding σ*Se-C orbital (n halogen→σ*Se-C). This inter-action leads to significant differences in the three-dimensional packing of the mol-ecules, which are assembled through π-π and C-H⋯π inter-actions. These data provide a better comprehension of the inter-molecular packing in benzo[b]chalcogenophenes, which is relevant for optoelectronic applications.

Asymmetric Catalytic Assembly of Triple‐Columned and Multilayered Chiral Folding Polymers Showing Aggregation‐Induced Emission (AIE)

Unprecedented chiral multilayer folding 3D polymers have been assembled and regulated by uniform and differentiated aromatic chromophore units between naphthyl piers. Screening catalysts, catalytic systems and monomers were proven to be crucial for asymmetric catalytic Suzuki-Miyaura polycouplings for this assembly. X-ray crystallography of the corresponding dimers and trimers revealed the absolute configuration and the intermolecular packing pattern. Up to 61 960 Mw /41 900 Mn and m/z 4317 for polymers and oligomers, as confirmed by gel permeation chromatography (GPC) and MALDI-TOF MS, indicated that these frameworks were composed of multiple stacked layers. The resulting multiple π-assemblies exhibited remarkable optical properties in aggregated states (photoluminescence in solids and aggregation-induced emission in solutions), as well as reversible redox properties in electrochemical performance.

The effect of substituents and their positions on a series of disubstituted naphthalene bromide salts towards intermolecular interactions and crystal packing

Naphthalene derived dications bearing different N-heterocyclic substituents appended at different positions demonstrated conformational flexibility and interesting self-assembled packing motifs when crystallised in the solid state as bromide salts.

Manipulating the D:A interfacial energetics and intermolecular packing for 19.2% efficiency organic photovoltaics

A novel electron acceptor, BTP-H2, demonstrates a high efficiency of 18.5% with a high Voc of 0.932 V. It also enables the ternary device to yield an efficiency of 19.2%, ranking the highest among single-junction organic photovoltaics.

Crystal structure and Hirshfeld surfaces analysis of Heterocyclic-and circulenes

The crystal structure of the new diazatrioxa[9]circulene and tetrahydro-diazatetraoxa[10]circulene which represent the first synthesized representatives of “higher” hetero[n]circulenes with n>8, was analyzed in details. Hirshfeld surface analyses, the dnorm surfaces and two-dimensional fingerprint plots were used to verify the contributions of the different intermolecular interactions within the crystal structure of diazatrioxa[9]circulene and tetrahydro-diazatetraoxa[10]circulene. The Hirshfeld surface analysis of the crystal structure clarifies that the most important contribution for crystal packing is from H∙∙∙H and C∙∙∙H intermolecular interactions for both circulenes. The shape-index surface shows that in the case of diazatrioxa[9]circulene two sides of the molecules are involved with the same contacts in neighbouring molecules and curvedness plots show flat surface patches that are characteristic of planar stacking. Such face-to-face structural organization provides the main charge transfer pathway in [9]circulene. In the case of [10]circulene, the area involved in the same contacts is much less, however, two types of intermolecular packing modes can form such flat surface patches at curvedness plots which is useful for more efficient charge transfer.

A High Energy X-ray Diffraction Study of Amorphous Indomethacin

Amorphous pharmaceuticals often possess a wide range of molecular conformations and bonding arrangements. The x-ray pair distribution function (PDF) method is a powerful technique for the characterization of variations in both intra-molecular and inter-molecular packing arrangements. Here, the x-ray PDF of amorphous Indomethacin is shown to be particularly sensitive to the preferred orientations of the chlorobenzyl ring found in isomers in the crystalline state. In some cases, the chlorobenzyl ring has no preferred torsional angle in the amorphous form, while in others evidence of distinct isomer orientations are observed. Amorphous samples with no preferred torsion angles of the chlorobenzyl ring are found to favor enhanced inter-molecular hydrogen bonding, and this is reflected in the intensity of the first sharp diffraction peak. These significant variations in structure rule out amorphous Indomethacin as a possible standard for x-ray PDF measurements. At high humidity, time resolved PDF's for >40 h reveal water molecules forming hydrogen bonds with Indomethacin molecules. A simple linear hydrogen bond model indicates that water molecules in the wet amorphous form have similar hydrogen bond strengths to those found between Indomethacin dimers or chains in the dry amorphous form.

Relationship Between Molecular Structure, Single crystal Packing and Self-Assembly Behavior: A Case Based on Pyrene Imide Derivatives.

Development of new n-type one-dimensional (1D) self-assembly nanostructure and a clear understanding of the relationship between molecular structure and self-assembly behavior are important prerequisites for further designing and optimizing organic optoelectronic nanodevice. In this article, a series of n-type organic semiconductor materials based on pyrene imide were successfully synthesized through [4+2] cycloaddition reactions and their preliminary optical and electrochemical properties were studied. The simulated HOMO-LUMO bandgaps via DFT tallied with the experimental data well. The self-assembly of these materials showed needle or fiber-like morphologies, indicating that different conjugation degree or alkyl group had significant influence on their self-assembly behaviors. Furthermore, the single-crystal packing for these molecules were analyzed and it was found out that the changes of conjugated backbone and functional group would affect certain crystal lattice parameter significantly, such as the intermolecular packing distance and crystal size etc, which would further result in different self-assembly morphology.

Strain-induced carrier mobility modulation in organic semiconductors

We systematically investigated the strain-induced carrier mobility of two representative n-type and p-type organic semiconductors, 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8), in order to understand the relationship between the carrier mobility and intermolecular packing configurations. The applied strain to organic semiconductors changes the intermolecular packing configurations, such as the π–π stacking distance and π–π overlap extent between adjacent π-conjugated molecules. In particular, the in-phase and out-of-phase π–π orbital interactions cause carrier mobility variations and energy level splitting by constructive/bonding and destructive/antibonding interactions between adjacent π-conjugated molecules. Our results demonstrate periodic changes of the strain-induced carrier mobility with respect to the π–π stacking distance and π–π overlap type, respectively. Furthermore, we propose that the periodic behaviors of carrier mobility can be attributed to the alternating phase changes of the molecular orbital interactions under applied strain. Based on the understanding of the intermolecular interactions and the structure–property relationships, we can provide a strain path for optimal carrier mobility modulation and the development of high-performance organic electronic devices.

Tunable aggregation-induced emission, solid-state fluorescence, and mechanochromic behaviors of tetraphenylethene-based luminophores by slight modulation of substituent structure

Herein, we report the synthesis of two AIE-active tetraphenylethene-derived luminogens with diethylamino (TPEDA) or pyrrolidino group (TPEPL) as terminal substituents, and systematically investigate the influence of diethylamino and pyrrolidino groups as terminal substituents on their photophysical properties and mechanochromic behavior. Single-crystal structural analyses verified that the free alkyl chains of the diethylamino groups were beneficial to loosen the intermolecular stacking. They exhibited distinct luminescence behaviors in the aggregated state. Compared with TPEDA, TPEPL displayed a long-wavelength solid-state fluorescence due to the more extended π-conjugation system across its intermolecular packing structure. However, TPEDA exhibited mechanochromic behavior that manifested in a larger red-shift (25 ​nm), which was attributed to its looser stacking mode. The work not only presents a better understanding of structure-property relationship, but also offers a new method for modulating intermolecular stacking and developing mechanochromic materials.

Simulation of absorption and scattering spectra of crystalline organic nanoparticles with the discrete dipole approximation: Effects of crystal shape, crystal size, and refractive indexof the medium.

The effect of the shape (habit) of crystalline organic nanoparticles on their absorption spectra is studied by simulations using the discrete dipole approximation, focusing, in particular, on the vibronic structure of the absorption bands in the spectra. Simulations predict a significant effect that, for sufficiently small particles, can be simply rationalized by the depolarization factor. The crystal size and the refractive indexof the medium in which the nanoparticles are embedded are also found to have an effect on the absorption spectra. All factors mentioned are found to influence also the spectra of scattered light. These effects, already broadly documented for metallic nanoparticles, are here demonstrated theoretically for the first time for crystalline organic nanoparticles, providing novel insight into the optical response of such particles. The effects are expected to be displayed by all organic nanoparticles, as long as they have a well-defined crystal structure and are large enough for the optical properties to be understandable using a macroscopic dielectric tensor. The effects demonstrated here should be taken into account when rationalizing differences in absorption spectra of a substance in solution and in nanoparticle form, e.g., in deducing the type of intermolecular packing. The effects are much less pronounced for optically isotropic nanoparticles.

Simple Nonfused‐Ring Electron Acceptors with Noncovalently Conformational Locks for Low‐Cost and High‐Performance Organic Solar Cells Enabled by End‐Group Engineering

AbstractThe rapid advance of fused‐ring electron acceptors (FREAs) has greatly promoted the leap‐forward development of organic solar cells (OSCs). However, the synthetic complexity of FREAs may be detrimental for future commercial applications. Recently, nonfused‐ring electron acceptors (NREAs) have been developed to be a promising candidate to maintain a rational balance between cost and performance, of which the cores are composed of simple fused rings (NREAs‐I) or nonfused rings (NREAs‐II). Moreover, “noncovalently conformational locks”, are used as an effective strategy to enhance the rigidity and planarity of NREAs and improve device performance. Herein, a novel series of NREAs‐II (PhO4T‐1, PhO4T‐2, and PhO4T‐3) is constructed as a valuable platform for exploring the impact of the end group engineering on optoelectronic properties, intermolecular packing behaviors, and device performance. As a result, a high power conversion efficiency of 13.76% is achieved for PhO4T‐3 based OSCs, which is much higher than those of the PhO4T‐1 and PhO4T‐2‐based devices. Compared with several representative FREAs, PhO4T‐3 possesses the highest figure‐of‐merit value of 133.45 based on a cost‐efficiency evaluation. This work demonstrates that the simple‐structured NREAs‐II are promising candidates for low‐cost and high‐performance OSCs.

Rational Management of Charge Transfer Character of Benzothienopyrimidine‐Based N‐Type Host for Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractTwo materials, 3‐(4‐(9H‐carbazol‐9‐yl)benzo[4,5]thieno[3,2‐d]pyrimidin‐2‐yl)‐5‐(triphenylsilyl)benzonitrile (CzBTPCNmSi) and 9‐(2‐(3‐(triphenylsilyl)phenyl)benzo[4,5]thieno[3,2‐d]pyrimidin‐4‐yl)‐9H‐carbazole‐3‐carbonitrile (CNCzBTPmSi), are synthesized as the N‐type host (electron‐transport type host) of a mixed host, harvesting triplet excitons of the blue phosphor by engineering the charge transfer character using a CN unit. The two host materials are based on benzothienopyrmidine modified using CN, tetraphenylsilyl, and carbazole groups to control the lowest unoccupied molecular orbital level, manage their intermolecular packing, and stabilize the molecule against holes, respectively. The two hosts are mixed with a P‐type 3,3‐di(9H‐carbazol‐9‐yl)biphenyl (mCBP) to offer a mixed host for sky and deep blue‐emitting phosphors. In the device applications, CzBTPCNmSi and CNCzBTPmSi show high external quantum efficiency (EQE) (around 24% in the sky‐blue devices), whereas only CNCzBTPmSi exhibited high EQE (above 20% in the deep blue devices) due to high triplet energy. Moreover, the CNCzBTPmSi demonstrates a longer device lifetime than the control host without the CN unit. Thus, CN engineering can manage the triplet energy, EQE, and device lifetime of blue phosphorescent devices by controlling the charge transfer character.

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Porous Pyrene Organic Cage with Unusual Absorption Bathochromic-Shift Enables Visible Light Photocatalysis

Modulation of Microstructure and Charge Transport in Polymer Monolayer Transistors by Solution Aging

Main observation and conclusionA few monolayers of organic semiconductors adjacent to the dielectric layer are of vital importance in organic field‐effect transistors due to their dominant role in charge transport. In this report, the 2‐nm‐thick polymer monolayers based on poly(3‐hexylthiophene) with different molecular weights (Mn) were fabricated using dip‐coating technique. During the monolayer (solid state) formation from the solution, a disorder‐to‐order transition of polymer conformation is observed through UV‐vis absorption measurement. Meanwhile, high Mn polymer monolayer generates higher crystalline fibrillar microstructure than the low Mn one due to the stronger π–π intermolecular packing between polymers. More importantly, the solution aging procedure is utilized to further improve the morphology of polymer monolayers. It is obvious that after aging for 6 d, both fiber dimension and density as well as conjugation length are significantly increased under the same processing conditions in comparison to the fresh solution, and consequently the field‐effect mobilities are remarkably enhanced by 2—4 times. Note that the maximum mobility of 0.027 cm2·V–1·s–1 is among the highest reported values for poly(3‐hexylthiophene) monolayer transistors. These results demonstrate a simple but powerful strategy for boosting the device performance of polymer monolayer transistors.

Supramolecular Assembly of a Terpyridyl based Binuclear Cu(II) Complex and its DNA Docking Study

ABSTRACT A terpyridyl-based binuclear Cu(II) complex, formulated as [Cu2(tpy)2(muco)(NO3)2], (1) (typ = 2,2’;6’,2”-terpyridine and H2-muco = trans, trans-muconic acid) was synthesised in a single pot technique using slow evaporation method. Blue coloured distorted octahedral-shaped crystals were obtained after a day. Synthesised compound has been characterised by elemental analysis as well as single crystal X-ray diffraction (SCXRD) techniques. Hirshfeld surface analysis has been explored to check out the nature of intermolecular interactions and packing modes of compounds in the crystalline state. From the docking study, it has been found that the metal complex bind to the major groove of DNA and the planner aromatic pyridine ring of the ligand partially intercalate into the base pairs.

Single‐Junction Organic Photovoltaic Cell with 19% Efficiency

Improving power conversion efficiency (PCE) is important for broadening the applications of organic photovoltaic (OPV) cells. Here, a maximum PCE of 19.0% (certified value of 18.7%) is achieved in single-junction OPV cells by combining material design with a ternary blending strategy. An active layer comprising a new wide-bandgap polymer donor named PBQx-TF and a new low-bandgap non-fullerene acceptor (NFA) named eC9-2Cl is rationally designed. With optimized light utilization, the resulting binary cell exhibits a good PCE of 17.7%. An NFA F-BTA3 is then added to the active layer as a third component to simultaneously improve the photovoltaic parameters. The improved light unitization, cascaded energy level alignment, and enhanced intermolecular packing result in open-circuit voltage of 0.879V, short-circuit current density of 26.7mA cm-2 , and fill factor of 0.809. This study demonstrates that further improvement of PCEs of high-performance OPV cells requires fine tuning of the electronic structures and morphologies of the active layers.

Fullerene-Based Triads with Controlled Alkyl Spacer Length as Photoactive Materials for Single-Component Organic Solar Cells.

Two kinds of dumbbell-shaped acceptor-donor-acceptor (A-D-A)-type triad single-component (SC) photovoltaic molecules based on a benzodithiophene-rhodanine (BDTRh) core and [6,6]-phenyl-C61 butyric acid (PC61BA) termini, BDTRh-C2-PC61BA and BDTRh-C10-PC61BA, were synthesized by modulating the alkyl (C2 and C10) spacer lengths. Both SC photovoltaic structures had similar UV-vis spectra in solution, but BDTRh-C10-PC61BA showed a significantly higher absorption coefficient as a thin film. In films, a more facile intermolecular photo-induced charge transfer was observed for BDTRh-C10-PC61BA in the broad-band transient absorption measurements. BDTRh-C10-PC61BA also exhibited a higher hole mobility (by 25 times) and less bimolecular recombination than BDTRh-C2-PC61BA. By plotting the normalized external quantum efficiency data, a higher charge-transfer state was measured for BDTRh-C10-PC61BA, reducing its voltage loss. A higher power conversion efficiency of ∼2% was obtained for BDTRh-C10-PC61BA, showing higher open-circuit voltage, short-circuit current density, and fill factor than those of BDTRh-C2-PC61BA devices. The different carrier dynamics, voltage loss, and optical and photoelectrical characteristics depending on the spacer length were interpreted in terms of the film morphology. The longer decyl spacer in BDTRh-C10-PC61BA afforded a significantly enhanced intermolecular ordering of the p-type core compared to BDTRh-C2-PC61BA, suggesting that the alkyl spacer length plays a critical role in controlling the intermolecular packing interaction.

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

Recent Advances in Molecular Design of Organic Thermoelectric Materials

Recent Advances in Molecular Design of Organic Thermoelectric Materials