Stacking Of Molecules Research Articles

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

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

Diameter-dependent single- and double-file stacking of squaraine dye molecules inside chirality-sorted single-wall carbon nanotubes.

The filling of single-wall carbon nanotubes (SWCNTs) with dye molecules has become a novel path to add new functionalities through the mutual interaction of confined dyes and host SWCNTs. In particular cases, the encapsulated dye molecules form strongly interacting molecular arrays and these result in severely altered optical properties of the dye molecules. Here, we present the encapsulation of a squaraine dye inside semiconducting chirality-sorted SWCNTs with diameters ranging from ∼1.15 nm, in which the dye molecules can only be encapsulated in a single-file molecular arrangement, up to ∼1.5 nm, in which two or three molecular files can fit side-by-side. Through the chirality-selective observation of energy transfer from the dye molecules to the surrounding SWCNTs, we find that the absorption wavelength of the dye follows a peculiar SWCNT diameter dependence, originating from the specific stacking of the dye inside the host SWCNTs. Corroborated by a theoretical model, we find that for each SWCNT diameter, the dye molecules adopt a close packing geometry, resulting in tunable optical properties of the hybrid when selecting a specific SWCNT chirality.

Structure, optical and electro-physical properties of tetramerized anion-radical salt (N-Xy-Qn)(TCNQ)2

The (N-Xy-Qn)(TCNQ)2 anion-radical salt characterized by tetramerized stacks of the TCNQ acceptor molecules has been synthesized and characterized using vibrational spectroscopy and electrical resistivity measurements. The bond lengths analysis based on the crystal structure data, indicates that the TCNQ molecules are non-uniformly charged with −0.83 e localized on the inner B molecules and −0.33 e on the outer A molecules within ABBA tetramers. Both infrared and Raman spectra of (N-Xy-Qn)(TCNQ)2 are dominated by vibrational modes of TCNQ and display splitting related to the tetramerized structure. Many of these features are affected by the strong electron-molecular vibration (EMV) coupling. Other charge-sensitive modes allowed estimation of charge localized on TCNQ, with the results that confirm the charges estimated on basis of the crystal data. Electrical measurements revealed the low-conducting behavior with room temperature conductivity value of 2.6 mS cm−1 and temperature dependence of resistivity that can be explained within the band conduction model. The calculated activation energies range from 0.169 eV to 0.187 eV, depending on the crystallographic direction and thermal history of the sample.

Theory of Apparent Circular Dichroism Reveals the Origin of Inverted and Noninverted Chiroptical Response under Sample Flipping.

Circular dichroism (CD) finds widespread application as an optical probe for the structure of molecules and supramolecular assemblies. Its underlying chiral light-matter interactions effectively couple between photonic spin states and select quantum-mechanical degrees of freedom in a sample, implying an intricate connection with photon-to-matter quantum transduction. However, effective transduction implementations likely require interactions that are antisymmetric with respect to the direction of light propagation through the sample, yielding an inversion of the chiroptical response upon sample flipping, which is uncommon for CD. Recent experiments on organic thin films have demonstrated such chiroptical behavior, which was attributed to "apparent CD" resulting from an interference between the sample's linear birefringence and linear dichroism. However, a theory connecting the underlying optical selection rules to the microscopic electronic structure of the constituent molecules remains to be formulated. Here, we present such a theory based on a combination of Mueller calculus and a Lorentz oscillator model. The theory reaches good agreement with experimental CD spectra and allows for establishing the (supra)molecular design rules for maximizing or minimizing this chiroptical effect. It furthermore highlights that, in addition to antisymmetrically, it can manifest symmetrically such that no chiroptical response inversion occurs, which is a consequence of a helical stacking of molecules in the light propagation direction.

In-situ self-organized anode interlayer enables organic solar cells with simultaneously simplified processing and greatly improved efficiency to 17.8%

Highly efficient organic solar cells (OSCs) are often obtained with a multilayer structure, in which active layer is sandwiched between anode and cathode interlayer. Here we present a simple strategy to simultaneously obtain anode interlayer and boost performances of OSCs by directly adding a tiny small molecule [2-(9H-carbazol-9-yl)ethyl] phosphonic acid (2PACz) into the active layer. It is found that 2PACz with high surface energy prefers to self-organize at the bottom of PM6:Y6-BO bulk heterojunction (BHJ) blend and in-situ form anode interlayer during the film formation. Encouragingly, green solvent o-xylene processed OSCs with substantial improvement of photovoltaic performances are observed in self-organized 2PACz device with best power conversion efficiency (PCE) reaching 17.8%, notably higher than that of control device based on independently spin-coated 2PACz with a PCE of 16.8%. In-depth studies indicate the in-situ self-organized 2PACz underneath BHJ is beneficial to enhance build-in potential, suppress surface trap-assisted recombination, and induce ordered molecule stacking. Moreover, this self-organization method is implanted in a large-area OSC with 1 cm2 device area and an outstanding PCE of 15.8% is achieved. These results above highlight the great potential of in-situ self-organization method in simplifying device processing as well as improving efficiency, which make it an ideal strategy for large-area OSCs manufacture.

Simple hybrid dithiafulvenes-triphenylamine systems as dopant-free hole-transporting materials for efficient perovskite solar cells

Two extended hybrid conjugated systems based on a triphenylamine (TPA) core with two and three peripheral 1,4-dithiafulvenes (DTF) units coded WH-2 and WH-3 as hole-transporting materials (HTMs) applied in perovskite solar cells (PSCs) are synthesized by facile one-step reaction in good yield over 75%. DTF unit as electron donor can enhance the electron donating ability and the fusion of benzenic ring of TPA with DTF unit may lead to reinforced intermolecular interactions in the solid state. In addition, WH-2 and WH-3 exhibit a pyramid shape containing partial planarity and quasi three-dimensionality features, which is also conducive to enhancing the π-π stacking of molecules in the solid state. The above-mentioned structural characteristics make the two HTMs have good hole mobilities. As a result, WH-2 and WH-3 obtained the high intrinsic hole mobilities of 4.69 × 10−4 and 2.18 × 10−3 cm2 V−1 s−1 respectively. Finally, the power conversion efficiencies (PCEs) of PSCs with WH-2 and WH-3 as cost-effective dopant-free HTMs are 15.39% and 19.22% respectively and the PCE of PSC with WH-3 is on a par with that of PSC with Li-TFSI/t-BP doped Spiro-OMeTAD (19.67%).

Reversible Photochromic Coordination Polymer by Phototriggered Subtle Molecular Conformation Variations.

Photochromic materials are constructed with molecules accompanied by structural change after triggering by light, which are of great importance and necessity for various applications. However, because of space-confinement effects, molecule stacking of these photoresponsive chromophores within coordination polymers (CPs) always results in an efficiency decrement and a response delay, and this phenomenon will lead to a poor photochromic property. Herein, a CP (named CIT-E) with a 3-fold-interpenetrating network structure, which was prepared with (Z)-1,2-diphenyl-1,2-bis[4-(pyridin-3-ylmethoxy)phenyl]ethene (1Z) and a CuI cluster, showed fast reversible photochromic behavior. Under UV-light illumination, the color of CIT-Z changed from pale yellow to reddish brown. With the illumination of green light, the polymer could return to its initial color within 10 s. To reveal the mechanism of reversible photochromic behavior of CIT-Z, single-crystal structures of each color state were fully studied, and other scientific study methods were also used, such as time-dependent density functional theory calculation and control experiments. It was found that, with light illumination, this behavior of CIT-Z was the result of a ligand-to-metal charge-transfer process, and this process was triggered by subtle molecular conformation variation of tetraphenylethylene. It should be noted that CIT-Z has high thermal and chemical stability, which are excellent advantages as smart photoresponsive materials. As a proof of concept, a uniform thin film with such a fascinating photochromic property allows applications in invisible anticounterfeiting and dynamic optical data storage. Overall, the present study opens up a new avenue toward reversible photochromic materials.

Convenient preparation of stimulus-responsive molecular layers containing anthracene molecules to control surface properties

For controlling the surface properties by depositing molecules on the material surface, the selection of the functional groups of the stacked molecules is crucial. By introducing anthracenes in the molecular layer, which promote photodimerization and thermal/cleavage on photoirradiation or heating, it is possible to form a stimuli-responsive surface that enables changes in the molecular layer composition. In this study, we improve the fabrication process of the stimulus-responsive molecular layer with anthracene in order to facilitate the design of molecular layers according to the desired purpose. This is achieved by employing acid-base interactions for forming the molecular layers, with different functions for each layer. Thermal/photocleavage reactions of anthracene dimers are induced in the stacked molecular layer. Multilayers stacked with amine molecules exhibit different behavior on the cleavage reaction and the contact angle varies, depending on the type of molecules. The wettability on the surface covered with the molecular layer changes in response to the stimulation, proving the successful fabrication of a stimuli-responsive surface. The designed thermo- and photoresponsive molecular layer can potentially expand the scope of practical application as a control system for surface conditions.

Synthesis and Characterization of Compounds Based on Carbazole and Sulfone Groups.

Two compounds containing carbazole and sulfone groups with different alkyl chain lengths have been designed and synthesized. The sulfone group has strong absorption characteristics and the alkoxy chain and carbazole group are electron-rich, forming D-δ-A-type symmetrical molecules. The molecules have the characteristics of charge transfer and high thermal stability, and the molecules stack to form a layered staggered stack, reducing the intermolecular π-π interactions. The target compounds also exhibit strong ultraviolet-fluorescent emission in the solid state at room temperature, and they are expected to be good luminescent materials.

Biphenyl-Induced Superhelix in l -Phenylalanine-Based Supramolecular Self-Assembly with Dynamic Morphology Transitions

Biphenyl-Induced Superhelix in <scp>l</scp> -Phenylalanine-Based Supramolecular Self-Assembly with Dynamic Morphology Transitions

Additive-free organic solar cells with enhanced efficiency enabled by unidirectional printing flow of high shear rate

High-performance OSCs prepared by scalable techniques without additives are highly desirable because residual additives may cause gradual deterioration of the photoactive-layer morphology and device performance. Printing flows with high shear rate have the potential to replace additives by inducing higher degree of ordered stacking and crystallinity of organic molecules, as well as favorable phase separation. Here, PTQ10:Y6 organic solar cells (OSCs) without any additives were fabricated by a scalable and robust processing approach termed as soft porous blade printing (SPBP). The fluid flow and drying process of the wet films made by SPBP, blade coating and spin coating are visualized by high speed imaging, which reveals that the blade coating and SPBP introduce unidirectional flow while the wet film interference pattern of spin coating is irregular and random. The simplified flow model of SPBP suggests that the shear rate could be as high as ~1000 s−1. The additive-free SPBP produces photoactive-layer with adequate morphology, which could be attributed to three intrinsic properties of SPBP: very high shear rate, flow assisted crystallizations induced by microstructures of the soft porous blade, and numerous nucleation sites generated as the liquid contact line follows the motion of the blade. The additive-free SPBP device demonstrates weaker charge recombination, higher and more balanced charge transport, and consequently better device performance than the spin-coated and blade-coated devices with 0.25 vol% 1,8-diioctane (DIO). SPBP achieved power conversion efficiency (PCE) of 16.45%, which is higher than those of spin-coated and blade-coated counterparts doped with DIO.

Facile synthesis of zein-based emulsion gels with adjustable texture, rheology and stability by adding β-carotene in different phases

The current study focused on the application of an agricultural byproduct, zein, to the formation of a novel type of emulsion gels. Zein based oil-in-glycerol emulsion gels (O/G ZEGs) were prepared by a facile one-step approach, and β-carotene was incorporated within the dispersed and continuous phases. β-Carotene could be interacted with zein, and thus the location of β-carotene significantly influenced the structures of O/G ZEGs. β-Carotene in the glycerol phase reduced the hardness of systems, but enhanced the viscosity, oil holding capacity and solvent binding capacity of the gels. Small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS) rheological analysis revealed that β-carotene in the oil phase enhanced the elastic properties of ZEGs and strengthened gel stability upon deformation. The gels with stronger mechanical properties were more capable to protect β-carotene when subjected to UV-light, and simultaneous loading of β-carotene in the oil phase and glycerol phase resulted in much lower degradation rate. However, the degradation of β-carotene also led to the weakening of gel networks. Microstructural observation suggested that β-carotene in oil phase facilitated the formation of much denser gels networks and more uniform distribution of oil droplets. FTIR tests verified that there were hydrophobic interactions between β-carotene and zein, which modified the stacking of zein molecules. This study first reported the roles of β-carotene in modulating the structures of zein based emulsion gels, and also provided information to expand the application of prolamins as efficient delivery systems for bioactives.

π‐Conjugated Small Molecules Modified SnO2 Layer for Perovskite Solar Cells with over 23% Efficiency

AbstractSnO2 has been universally applied as electron transporting layer (ETL) towards the fabrication of highly efficient perovskite solar cells (PSCs), owing to its unique advantages including low‐temperature solution‐processability, high optical, transmittance and good electrical conductivity. Uncoordinated Sn‐dangling bonds on SnO2 surface exist as deep traps to capture the photogenerated carriers, causing hysteresis and device instability. Fullerene derivatives, though being widely utilized as the passivator for SnO2, are highly prone to self‐aggregate due to their π‐cage structures, which hampers passivation. Herein, π‐conjugated n‐type small molecules with better film formation ability are innovatively designed, to improve passivation effectiveness. By exploring the interplay between molecular stacking of small molecules and charge transporting/recombination dynamics at the SnO2/perovskite interface, it is unveiled that a more compact molecular packing of the organic passivators yields superior interfacial characteristics, in terms of fewer trap states, lower charge recombination and higher electron transporting efficiency. An impressive PCE over 23% is achieved with the assistance of this new‐type SnO2‐passivator, which is among the highest reported value for triple‐cation perovskite systems to date. This work offers an original concept for the design and synthesis of ETL passivators towards the development of high performance and stable PSCs.

In Situ Exploration of Stimulus-Induced Emission Changes in Mechanochromic Dyes.

The development of in situ analysis techniques for visualizing and linking macro- and nanoscopic features of external stimulus-responsive materials is crucial for their rational design and applications. Herein, we investigate the mechanical stress-induced emission changes in electron donor-acceptor type organic dye molecules in solid states through in situ single-particle fluorescence spectroscopy combined with macroscopic and nanoscopic stimulation systems. The change in emission color from green to yellow was attributed to repeated rubbing or scratching of the crystal surface, and not to simple cutting. This change was due to partial amorphization, which changed the intra- and intermolecular charge-transfer interactions of stacked molecules near the surface. We believe that this study will facilitate the efficient design of mechano-responsive materials with finely controlled and responsive properties.

Enhanced Hydrodynamic Radius of AOT/n-heptane/Water Reverse Micellar System Through Altered Electrostatic Interactions and Molecular Self-Assemblies.

We have demonstrated a unique approach to alter the aqueous pool size of an AOT/n-heptane/water reverse micellar system. A positively charged dye Rhodamine B (RhB) and negatively charged Rose Bengal (RB) were incorporated in the reverse micellar pool to investigate the effect of electrostatic interactions and stacking effects among the dye molecules on the AOT/n-heptane/water interface. Dynamic light scattering revealed increase in reverse micellar pool size in presence of positively charged dye aggregates at the oil-water interface. However, less expansion was observed in presence of negatively charged dye aggregates (RB). This confirms the role of electrostatic interaction in modulating the hydrodynamic radius. A head-to-tail type of stacking of RhB molecules at the interface favors this expansion. The differences in stacking of the two dyes inside the reverse micelles and their torsional mobility indicated the role of the reverse micellar interface and H-bonding ability of the microenvironment on dye aggregation. Conductivity measurements demonstrated a significant drop in percolation temperature of the reverse micellar system in presence of dye aggregates. This confirms the effect of dye aggregation and electrostatic interaction on such expansion. This strategy can be exploited for solubilizing greater amounts and a wider variety of drug molecules in microemulsions.

Construction of Layered High-Energy Materials via Directional Hydrogen Bonding

Energetic substances with layered crystal packing have been identified as the most promising next-generation high-energy materials (HEMs) due to their excellent insensitivity. The challenge, however, is how to design layered HEMs. In this study, a novel strategy called “acceptor–donor separation” was proposed to control the layer-by-layer stacking of energetic molecules through directional hydrogen boding: that is, a hydrogen bond donor and acceptor are located in different energetic segments and at least one of them has a conjugated planar structure, which will enable the energetic fragments to be infinitely extended in a two-dimensional plane to form a target layered structure. The experimental results showed that three exemplary substances designed by using this strategy possess the expected layered structures, which have been confirmed by single-crystal X-ray diffraction, demonstrating the robustness of this strategy. Moreover, the three as-synthesized HEMs all exhibit excellent insensitivity (impact sensitivity IS > 40 J; friction sensitivity FS > 360 N), affording safety far beyond those of the most powerful HEMs in use today. Especially, the hydroxylammonium energetic salts possess good detonation performance (detonation velocity D = 8924 m s–1; detonation pressure P = 36.9 GPa) comparable to that of 1,3,5-trinitro-1,3,5-triazine (RDX), one of the most powerful high explosives in use today.

Sorption mechanisms of pesticides removal from effluent matrix using biochar: Conclusions from molecular modelling studies validated by single-, binary and ternary solute experiments

Sorption of atrazine (ATZ), imidacloprid (IMIDA) and azoxystrobin (AZOXY) in single-, bi- and ternary-solutes system was modelled using phosphoric acid-treated rice straw biochar (T-RSBC). The T-RSBC showed stronger sorption capacity for IMIDA in single- and bi-solute systems. The Freundlich constant (KFads) in ternary system followed the order: ATZ (222.7) < IMIDA (1314) < AZOXY (1459). Adsorption modeling and molecular dynamics suggested that non-bonding interactions between aromatic groups and electrostatic interactions with the phosphate ester group in T-RSBC played an important role. Enhanced sorption by pore-filling may be attributed to the stacking of pesticide molecules in the form of multilayer. IMIDA was predominantly sorbed by pore-filling mechanism, whereas, ATZ adsorbed by partitioning mechanism. The percent removal of three pesticides in waste water effluent followed the order: AZOXY > IMIDA > ATZ. The Freundlich isotherm based multicomponent Sheindorf-Rebuhn-Sheintuch equation's suggested that the extent of ATZ adsorption, in the presence of co-habiting pesticides, decreased with increase in number of solutes (KiATZ, Singlev> KiATZ, Binary> KiATZ, Ternary). The competitive coefficient values (αATZ/IMIDA, Ternary > αATZ/AZOXY,Ternary) revealed that ATZ adsorption in ternary system was inhibited more by the presence of IMIDA than AZOXY. Findings suggested that biochar with a large fraction of non-carbonized phase promoted non-competitive sorption.

Correlating the Molecular Structure of A‐DA′D‐A Type Non‐Fullerene Acceptors to Its Heat Transfer and Charge Transport Properties in Organic Solar Cells

AbstractEfficient heat transfer is beneficial to heat dissipation and the thermal durability of organic solar cell (OSCs). In this regard, heat transfer properties of organic semiconductors within OSCs should play important roles, but their thermal properties are rarely explored. Here, heat diffusion properties of Y‐series non‐fullerene acceptors processing different DA′D framework, named BZ4F‐5, BZ4F‐6, and BZ4F‐7 are probed; it is found that backbone rings extension from five‐ to six‐ and seven‐membered‐fused rings trigger longer phonon mean free path and higher thermal diffusivities (D) in their pristine solid films and bulk heterojunction blends. Particularly, the correlation between the thermal transport properties in Y‐series acceptors and their backbone geometry, molecule stacking, and thin‐film crystallinity is demonstrated. More importantly, both organic thin‐film transistors and OSCs confirm that thermal durability of organic semiconductor devices correlated with the thermal properties of their active layer. Although BZ5F‐6 and BZ4F‐7 based devices possess similar device performance at room temperature, superior heat dissipation in BZ4F‐7 molecule endows it with enhanced device lifetime. These results contribute to critical design criteria for future molecular optimization in photovoltaic and optoelectronic devices.

Liquid-crystalline 1,4-benzoquinone derivative: Self-assembling behavior and redox properties

1,4-Benzoquinone has an important structural motif and target to develop compounds for pharmacology, organic electronic, and natural products. Herein, we synthesized and characterized a series of benzoquinone derivatives BQ, BQ2, and BQ4. Cyclic voltammetry showed that BQ2 and BQ4 have both electron-accepting and electron-donating properties. X-ray diffraction, polarized optical microscopic observations, and DSC measurement indicated that BQ4 self-assembled into the hexagonal columnar liquid-crystalline (LC) phase in the wide temperature range including room temperature, whereas BQ2 was crystal. We carried out the single crystal X-ray analysis of BQ to investigate the molecular arrangement of benzoquinone cores in the column LC phase of BQ4, in which each benzoquinone core was isolated by surrounding of four phenyl moieties not to interact with each other. Also, BQ was nonpolar evaluated by density functional theory (DFT) calculations. As a result, propeller-like BQ4 molecules stack into the column structures dependent on molecular shape.

Base pair fluctuations in helical models for nucleic acids.

A statistical method is developed to estimate the maximum amplitude of the base pair fluctuations in a three dimensional mesoscopic model for nucleic acids. The base pair thermal vibrations around the helix diameter are viewed as a Brownian motion for a particle embedded in a stable helical structure. The probability to return to the initial position is computed, as a function of time, by integrating over the particle paths consistent with the physical properties of the model potential. The zero time condition for the first-passage probability defines the constraint to select the integral cutoff for various macroscopic helical conformations, obtained by tuning the twist, bending, and slide motion between adjacent base pairs along the molecule stack. Applying the method to a short homogeneous chain at room temperature, we obtain meaningful estimates for the maximum fluctuations in the twist conformation with ∼10.5 base pairs per helix turn, typical of double stranded DNA helices. Untwisting the double helix, the base pair fluctuations broaden and the integral cutoff increases. The cutoff is found to increase also in the presence of a sliding motion, which shortens the helix contour length, a situation peculiar of dsRNA molecules.