Molecular Packing Research Articles

Tailoring Cyano Substitutions on Quinoxaline‐based Small‐Molecule Acceptors Enabling Enhanced Molecular Packing for High‐Performance Organic Solar Cells

AbstractCyanation is a common chemical modification strategy to fine‐tune the energy levels and molecular packing of organic semiconductors, especially materials used in organic solar cells (OSCs). Generally, cyanation is used to modify the end groups of high‐performance small‐molecule acceptors (SMAs). However, the cyanation strategy has not been investigated on the central backbone of SMAs, which could introduce stronger intermolecular interaction and enhance the π–π stacking for rapid charge transport. This paper, for the first time, reports a new cyanation strategy on the central benzo‐quinoxaline core and synthesizes two novel A‐DA'D‐A type SMAs, named BQx‐CN and BQx‐2CN, with mono‐ and di‐cyanide groups, respectively. Through tailoring the number of CN groups, the BQx‐CN‐based OSC exhibits the best device performance of 18.8%, which is significantly higher than the non‐cyano BQx‐based one. The reason for the superior performance of BQx‐CN‐based devices can be attributed to the fine‐tuned energy level, stronger packing, and ideal phase segregation, which lead to superior exciton dissociation, faster charge transport, and suppressed recombination, therefore the highest fill factor (FF) and power conversion efficiencies (PCE). The research demonstrates the effectiveness of the cyanation strategy on the central core of SMAs for enhanced molecular packing and better performance of OSCs.

Synthesis of Perylene Diimide Modified by POSS and its Assembly Behavior in Solution and SBS Matrix

In this work, Perylene diimide derivatives 1,7- POSS-PDI-C12 (PPC) were synthesized using 1,7-Br-PDI- C12, 18-crown-6 ether as phase transfer agent, K2CO3 as catalyst and THF as solvent in a reaction system. Subsequently, the POSS-SH group was successfully introduced into the perylene imide bay site in high yield. The chemical structure and molecular weight of the products were characterized by 1H-NMR, 13C-NMR, MALDI-TOF MS and FT-IR. The self-assembly behavior in different solvents was studied using the research solution self-assembly method. PPC remained in a single monomolecular state due to the bulky POSS group, which introduced large steric hindrance in the molecular packing, leading to the weakening of the π–π interactions. Then, the Composite thin films containing PPC in SBS was prepared. PPC do not exhibit significant force-chromic behavior owing to the dispersion of single- molecule states. This shows that in the construction of mechanochromic materials, chromophore molecules need to have a certain degree of aggregation in the matrix, but the aggregation degree should not be too high.

Optimizing Molecular Packing via Steric Hindrance for Reducing Non-Radiative Recombination in Organic Solar Cells.

Innovative molecule design strategy holds promise for the development of next-generation acceptor materials for efficient organic solar cells with low non-radiative energy loss (ΔEnr). In this study, we designed and prepared three novel acceptors, namely BTP-Biso, BTP-Bme and BTP-B, with sterically structured triisopropylbenzene, trimethylbenzene and benzene as side chains inserted into the shoulder of the central core. The progressively enlarged steric hindrance from BTP-B to BTP-Bme and BTP-Biso induces suppressed intramolecular rotation and altered the molecule packing mode in their aggregation states, leading to significant changes in absorption spectra and energy levels. By regulating the intermolecular π-π interactions, BTP-Bme possesses relatively reduced non-radiative recombination rate and extended exciton diffusion lengths. The binary device based on PB2:BTP-Bme exhibits an impressive power conversion efficiency (PCE) of 18.5% with a low ΔEnr of 0.19 eV. Furthermore, the ternary device comprising PB2:PBDB-TF:BTP-Bme achieves an outstanding PCE of 19.3%. The molecule design strategy in this study proposed new perspectives for developing high-performance acceptors with low ΔEnr in OSCs.

Side‐chain symmetry‐breaking strategy on porphyrin donors enables high‐efficiency binary all‐small‐molecule organic solar cells

AbstractSide‐chain symmetry‐breaking strategy plays an important role in developing photovoltaic materials for high‐efficiency all‐small‐molecule organic solar cells (ASM OSCs). However, the power conversion efficiencies (PCEs) of ASM OSCs still lag behind their polymer‐based counterparts, which can be attributed to the difficulties in achieving favorable morphology. Herein, two asymmetric porphyrin‐based donors named DAPor‐DPP and DDPor‐DPP were synthesized, presenting stronger intermolecular interaction and closer molecular stacking compared to the symmetric ZnP‐TEH. The DAPor‐DPP:6TIC blend afforded a favorable morphology with nanoscale phase separation and more ordered molecular packing, thus achieving more efficient charge transportation and suppressed charge recombination. Consequently, the DAPor‐DPP:6TIC‐based device exhibited superior photovoltaic parameters, yielding a champion PCE of 16.62% higher than that of the DDPor‐DPP‐based device (14.96%). To our knowledge, 16.62% can be ranked as one of the highest PCE values among the binary ASM OSC filed. This work provides a prospective approach to address the challenge of ASM OSCs in improving film morphology and further achieving high efficiency via side‐chain symmetry‐breaking strategy, exhibiting great potential in constructing efficient ASM OSCs.

Optimizing Molecular Packing via Steric Hindrance for Reducing Non‐Radiative Recombination in Organic Solar Cells

Innovative molecule design strategy holds promise for the development of next‐generation acceptor materials for efficient organic solar cells with low non‐radiative energy loss (ΔEnr). In this study, we designed and prepared three novel acceptors, namely BTP‐Biso, BTP‐Bme and BTP‐B, with sterically structured triisopropylbenzene, trimethylbenzene and benzene as side chains inserted into the shoulder of the central core. The progressively enlarged steric hindrance from BTP‐B to BTP‐Bme and BTP‐Biso induces suppressed intramolecular rotation and altered the molecule packing mode in their aggregation states, leading to significant changes in absorption spectra and energy levels. By regulating the intermolecular π‐π interactions, BTP‐Bme possesses relatively reduced non‐radiative recombination rate and extended exciton diffusion lengths. The binary device based on PB2:BTP‐Bme exhibits an impressive power conversion efficiency (PCE) of 18.5% with a low ΔEnr of 0.19 eV. Furthermore, the ternary device comprising PB2:PBDB‐TF:BTP‐Bme achieves an outstanding PCE of 19.3%. The molecule design strategy in this study proposed new perspectives for developing high‐performance acceptors with low ΔEnr in OSCs.

Boosting the performance of polymer field-effect transistors through fluorine atom substitutions and comparing the effect of various acceptor units and channel mobilities

Three conjugated copolymers, PDPP-2FTVT, PIID-2FTVT, and PNDI-2FTVT based on the 2,2′-(1E)-1,2-ethenediylbis[3-fluorothiophene] (2FTVT) core with varying acceptor units, diketopyrrolopyrrole (DPP), isoindigo (IID), and naphthalenediimide (NDI) were developed for organic field-effect transistors (OFETs). Combined electron-withdrawing fluorine atoms and vinyl linkage in the 2FTVT unit not only reduce the frontier molecular orbital energies but also extended the absorption profile and planarize the polymer backbone, manifesting synergetic effect on the strengthened molecular interactions and charge-carrier properties. The resulted copolymer, PDPP-2FTVT show highly reliable thin film transistor properties with highest hole mobility of 1.93 cm2 V−1 s−1 compared to PIID-2FTV and PNDI-2FTVT. PIID-2FTV copolymer show ambipolar characteristic with hole and electron mobilities of 0.71 and 0.03 cm2 V−1 s−1 respectively while PNDI-2FTVT exhibited the highest electron mobility of 0.20 cm2 V−1 s−1 among three copolymers. Thin film micro-structure characterization reveal that the three copolymers formed lamellar, edge-on molecular packing (for PDPP-2FTVT and PIID-2FTV), increased crystallinity with smaller π-π stacking distances, and strengthen the planarity after thermal annealing. These results contribute important progresses in solution-processed OFET and could provide a greater possibility of 2FTVT based copolymers for commercial application.

Hierarchical Self-Assembly of Multidimensional Functional Materials from Sequence-Defined Peptoids.

Hierarchical self-assembly represents a powerful strategy for the fabrication of functional materials across various length scales. However, achieving precise formation of functional hierarchical assemblies remains a significant challenge and requires a profound understanding of molecular assembly interactions. In this study, we present a molecular-level understanding of the hierarchical assembly of sequence-defined peptoids into multidimensional functional materials, including twisted nanotube bundles serving as a highly efficient artificial light harvesting system. By employing synchrotron-based powder X-ray diffraction and analyzing single crystal structures of model compounds, we elucidated the molecular packing and mechanisms underlying the assembly of peptoids into multidimensional nanostructures. Our findings demonstrate that incorporating aromatic functional groups, such as tetraphenyl ethylene (TPE), at the termini of assembling peptoid sequences promotes the formation of twisted bundles of nanotubes and nanosheets, thus enabling the creation of a highly efficient artificial light harvesting system. This research exemplifies the potential of leveraging sequence-defined synthetic polymers to translate microscopic molecular structures into macroscopic assemblies. It holds promise for the development of functional materials with precisely controlled hierarchical structures and designed functions.

Self‐Assembled Cyclotriguaiacyclene‐Integrated Supramolecular Systems for Liquid Crystal and Self‐Assembly Behavior

AbstractAn advanced tri‐substituted supramolecular material was synthesized via conversion of cyclotriveratrylene to cyclotriguaiacyclene with further esterification reaction with fluorescein unit embedded with side‐arms. All four luminescent materials exhibited columnar hexagonal type mesophase on both heating and cooling conditions. The materials with hexadecyloxy and octadecyloxy tail group exhibit liquid crystalline behavior at room temperature indicating the presence of a mesophase even under ambient conditions. By combining polarizing optical microscopy, differential scanning calorimetry, and high‐temperature X‐Ray diffraction techniques to understanding the optical, thermal, and molecular packing behavior of the compounds in the liquid crystalline state. The cyclotriguaiacyclene core with high fluorescent nature displayed columnar hexagonal type self‐assembly at room temperature. All four supramolecular mesogens showed higher thermal stability of mesophase. The computational study provides the importance of the electronic nature of the compounds.

Hierarchical Self‐Assembly of Multidimensional Functional Materials from Sequence‐Defined Peptoids

AbstractHierarchical self‐assembly represents a powerful strategy for the fabrication of functional materials across various length scales. However, achieving precise formation of functional hierarchical assemblies remains a significant challenge and requires a profound understanding of molecular assembly interactions. In this study, we present a molecular‐level understanding of the hierarchical assembly of sequence‐defined peptoids into multidimensional functional materials, including twisted nanotube bundles serving as a highly efficient artificial light harvesting system. By employing synchrotron‐based powder X‐ray diffraction and analyzing single crystal structures of model compounds, we elucidated the molecular packing and mechanisms underlying the assembly of peptoids into multidimensional nanostructures. Our findings demonstrate that incorporating aromatic functional groups, such as tetraphenyl ethylene (TPE), at the termini of assembling peptoid sequences promotes the formation of twisted bundles of nanotubes and nanosheets, thus enabling the creation of a highly efficient artificial light harvesting system. This research exemplifies the potential of leveraging sequence‐defined synthetic polymers to translate microscopic molecular structures into macroscopic assemblies. It holds promise for the development of functional materials with precisely controlled hierarchical structures and designed functions.

Unraveling the influence of surface functionalities on gas Physisorption: A comprehensive study on SBA-15 nanoporous material from Monte Carlo simulation for improved Textural-Energetic characterization

In this study, we conducted experimental and Monte Carlo simulation studies in the grand canonical ensemble (GCMC) to investigate the role of molecular orientation and surface heterogeneity on the adsorption of N2 at 77 K. Our research focused on a series of ordered nanoporous materials (SBA-15) with varying degrees of oxygen functionalities. Specifically, we examined the effects of surface heterogeneity on the calculation of pore size distribution (PSD) and the Brunauer-Emmett-Teller (BET) area of porous materials. To provide a comprehensive perspective, we compared our results with three levels of surface oxidation, including a pristine case without any surface oxidation.The results from both our experimental and simulation data reveal the importance of chemical heterogeneity in determining equilibrium properties such as molecular packing within the pores, differential enthalpies of adsorption, and N2 orientation distribution. Our findings suggest that accurate characterization of surface heterogeneity is crucial for understanding gas adsorption in nanoporous materials and for developing better models for predicting their performance in various applications. Moreover, our simulations revealed substantial changes in the molecular orientation of adsorbate particles with increasing surface heterogeneity. This insight provides valuable information about the behavior of molecules within the nanoporous materials, further enhancing our understanding of the complex adsorption processes in these systems.

On the properties of water in betaine – Based Deep eutectic solvents

Deep eutectic solvents have gained attention as environmentally friendly alternatives in various technological applications. Likewise, it is known the relevant effect of water on the physicochemical properties of Deep Eutectics, especially for hydrophilic ones. In this study, Betaine – based type III Deep Eutectic solvents (with ethylene glycol, fructose, malic acid or citric acid as Hydrogen Bond Donors) are considered and the properties and structuring of water in Deep Eutectic solutions (content lower than 20 %) were investigated considering volumetric properties, optical properties (refraction index), dynamic properties (viscosity, thermal conductivity, and electrical conductivity) as well as relevant characteristics for liquid phase nature such as polarizability and molecular packing. Viscosity measurements demonstrated a wide variation in viscosities, with water content playing a significant role, thus probing how water content largely affect dynamic properties of Deep Eutectics. Additionally, high water content led to improved thermal and electrical conductivity, particularly in mixtures containing citric acid and malic acid as Hydrogen Bond Donors. The polarizability decreased with increasing water content, and packing calculations indicated that the most voluminous molecules occupied interstitial voids. Our findings contribute to the understanding of water in Deep Eutectics solution, aiding their optimization for sustainable applications.

Insights on molecular modeling and supramolecular arrangement of bilastine polymorphs.

The advancement in the development of second-generation drugs in the field of antihistamines represents a significant milestone in the management of allergic diseases, targeting the effects of histamine. The efficacy of bilastine in treating allergic disorders has sparked interest in investigating its polymorphism, a crucial property that impacts quality, safety, and effectiveness as per regulatory guidelines. This study examines the polymorphism of bilastine, focusing on two crystalline forms labeled as Form I and Form II. Utilizing advanced analytical techniques, the research explores the structural characteristics and molecular interactions within these forms. Geometric parameters, such as bond lengths, bond angles, and torsion angles, are examined to comprehend molecular conformations and crystal packing arrangements. Hydrogen bonding, covalent bonds, and van der Waals forces contribute to the unique supramolecular arrangements in these forms.This study provides a significant contribution to understanding bilastine's polymorphism, offering critical insights to researchers and regulatory bodies to ensure the quality, efficacy, and safety of antihistamine products. The molecular conformation of two bilastine forms was obtained through DFT with the exchange-correlation functional M06-2X and the 6-311 +  + G(d,p) basis set, and the results were compared with the experimental X-ray. The atomic coordinates were obtained directly from the crystalline structures, and charge transfer was also investigated using frontier molecular orbitals (HOMO and LUMO), and MEP map in order to evaluate the energies associated with charge transfers and regions of high electron affinity. The geometric and topological parameters and intermolecular interactions in the crystals were analyzed using Hirshfeld Surface.

Crystal structure and Hirshfeld surface analysis of (Z)-4-({[2-(benzo[b]thio-phen-3-yl)cyclo-pent-1-en-1-yl]meth-yl}(phen-yl)amino)-4-oxobut-2-enoic acid.

In the title compound, C24H21NO3S, the cyclopentene ring adopts an envelope conformation. In the crystal, mol-ecules are linked by C-H⋯π inter-actions, forming ribbons along the a axis. Inter-molecular C-H⋯O hydrogen bonds connect these ribbons to each other, forming layers parallel to the (01) plane. The mol-ecular packing is strengthened by van der Waals inter-actions between the layers. The inter-molecular contacts were qu-anti-fied using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H⋯H 46.0%, C⋯H/H⋯C 21.1%, O⋯H/H⋯O 20.6% and S⋯H/H⋯S 9.0%.

Molecularly Thin 2D Organic Single Crystals: A New Platform for High-Performance Polarization-Sensitive Phototransistors.

The inherent linear dichroism (LD), high absorption, and solution processability of organic semiconductors hold immense potential to revolutionize polarized light detection. However, the disordered molecular packing inherent to polycrystalline thin films obscures their intrinsic diattenuation, resulting in diminished polarization sensitivity. In this study, we develop filter-free organic polarization-sensitive phototransistors (PSPs) with both a high linear dichroic ratio (LDR) and exceptional photosensitivity utilizing molecularly thin dithieno[3,2-b:2',3'-d]thiophene derivatives (DTT-8) two-dimensional molecular crystals (2DMCs) as the active layer. The orderly molecular packing in 2DMCs amplifies the inherent LD, and their molecular-scale thickness enables complete channel depletion, significantly reducing the dark current. As a result, PSPs with an impressive LDR of 3.15 and a photosensitivity reaching 3.02 × 106 are obtained. These findings present a practical demonstration of using the polarization angle as an encryption key in optical communication, showcasing the potential of 2DMCs as a viable and promising category of semiconductors for filter-free, polarization-sensitive photodetectors.

A 3,3'-Difluoro-2,2'-Bithiophene Based Donor Polymer Realizing High Efficiency (>17%) Single Junction Binary Organic Solar Cells.

In this study, two novel donor-acceptor (D-A) copolymers are designed and synthesized, DTBT-2T and DTBT-2T2F with 2,2'-bithiophene or 3,3'-difluoro-2,2'-bithiophene as the donor unit and dithienobenzothiadiazole as the acceptor unit, and used them as donor materials in non-fullerene organic solar cells (OSCs). Due to enhanced planarity of polymer chains resulted by the intramolecular F···S noncovalent interactions, the incorporation of 3,3'-difluoro-2,2'-bithiophene unit instead of 2,2'-bithiophene into the polymers can enhance their molecular packing, crystallinity and hole mobility. The DTBT-2T:L8-BO based binary OSCs deliver a power conversion efficiency (PCE) of only 9.71% with a Voc of 0.78V, a Jsc of 20.69mAcm-2 , and an FF of 59.67%. Moreover, the introduction of fluoro atoms can lower the highest occupied molecular orbital levels. As a result, DTBT-2T2F:L8-BO based single-junction binary OSCs exhibited less recombination loss, more balanced charge mobility, and more favorable morphology, resulting in an impressive PCE of 17.03% with a higher Voc of 0.89V, a Jsc of 25.40mAcm-2, and an FF of 75.74%. These results indicate that 3,3'-difluoro-2,2'-bithiophene unit can be used as an effective building block to synthesize high performance polymer donor materials. This work greatly expands the selection range of donor units for constructing high-performance polymers.

Intrinsically Stretchable Polymer Semiconductor with Regional Conjugation for Stretchable Electronics

AbstractThe development of intrinsically stretchable polymer semiconductor holds substantial promise in the field of wearable electronics. However, charge transport mobility is typically compromised in existing stretchable semiconductors to achieve the desired stretchability. Herein, a novel “regional conjugation” strategy is proposed to design an intrinsically stretchable polymer semiconductor oligo‐diketopyrrolopyrrole‐thieno[3,2‐b]thiophene (DPPTT)–urethane, in which oligo‐DPPTT conjugated units and alkyl urethane nonconjugated units are introduced. The regional conjugation of oligo‐DPPTT in the polymer backbone endows DPPTT–urethane with good molecular packing, leading to a high mobility of up to 1.7 cm2 V−1 s−1. Additionally, incorporating alkyl urethane nonconjugated units in the backbone can reduce film crystallinity and chain aggregation, which contribute to the stretchability of the polymer thin film. Consequently, fully stretchable transistors retain carrier mobility even at 100% biaxial tensile strain. Furthermore, the fully stretchable organic field‐effect transistor arrays show remarkable charge transport reversibility and durability after 1000 stretch–release cycles at 25% strain. Additionally, the device exhibits extraordinary electrical stability in air atmosphere. Overall, these results indicate that the “regional conjugation” strategy provides an effective and promising methodology to design intrinsically stretchable and high‐performance polymer semiconductor that can advance the development of soft and wearable electronics.

Unraveling the influence of aromatic endcaps in peptide self-assembly

Aromatic peptides are an emerging class of building units for molecular self-assembly and creation of functional biomaterials. The strength of aromatic association plays an essential role in the self-assembly of aromatic peptides. Here, we design a series of aromatic peptides with different hydrophobic domains but the same peptide sequence. The hydrophobicity and aromaticity can be carefully regulated by the number of benzene rings and the alkyl spacer between the benzene and peptide regions. Upon the continuous enhancement of aromaticity, diverse supramolecular nanostructures, including nanotubes, nanofibers, and short helical ribbons, were clearly observed. The peptide with diphenyl groups exhibits the highest regularity of molecular packing, due to the synergy of force balance between hydrogen bonding and π–π interactions. In addition, the incorporation of a spacer in between the aromatic and peptide regions facilitates the self-assembly capability, as the interference between aromatic association and hydrogen bonding is hindered. These dramatic results demonstrate that aromaticity serves as an effective and robust parameter in the molecular arrangement, providing a new perspective into the formation and evolution of supramolecular assembly.

Heliconical nematic and smectic phases: the synthesis and characterisation of the CB4O.m and CB8O.m series

ABSTRACT The synthesis and characterisation of two series of nonsymmetric dimers belonging to the family of compounds, the 1-(4-cyanobiphenyl-4′-yl)-ω-(4-alkylanilinebenzylidene-4′-oxy)alkanes (CBnO.m) is reported; in the acronym, n refers to the number of carbon atoms in the spacer, and m in the terminal alkyl chain. The two series reported, CB4O.m and CB8O.m, both show twist-bend nematic (NTB) and smectic phases (SmCTB-SH and SmCTB-DH). Their phase behaviour is compared to that of the CB6O.m and CB10O.m series. For each series, locally intercalated molecular packing is observed for short terminal chains and interdigitated packing for long terminal chains. The intercalated anticlinic smectic CA phase is observed for the CB8O.m and CB10O.m series. All four series exhibit the SmCTB-SH and SmCTB-DH phases for the longer terminal chains and all have an interdigitated molecular arrangement. The absence of an intercalated heliconical phase is attributed to the high viscosity associated with the network intercalated structure.

π-Extended Nonfullerene Acceptor for Compressed Molecular Packing in Organic Solar Cells To Achieve over 20% Efficiency.

Organic photovoltaics (OPVs) suffer from a trade-off between efficient charge transport and suppressed nonradiative recombination due to the aggregation-induced luminance quenching of organic semiconductors. To resolve this grand challenge, a π-extended nonfullerene acceptor (NFA) B6Cl with large voids among the honeycomb network is designed and introduced into photovoltaic systems. We find that the presence of a small amount of (i.e., 0.5 or 1 wt %) B6Cl can compress the molecular packing of the host acceptor L8-BO, leading to shortened π-π stacking distance from 3.59 to 3.50 Å (that will improve charge transport) together with ordered alkyl chain packing (that will inhibit nonradiative energy loss due to the suppressed C-C and C-H bonds vibrations), as validated by high-energy X-ray scattering measurements. This morphology transformation ultimately results in simultaneously improved JSC, FF, and VOC of OPVs. As a result, the maximum PCEs of PM6:L8-BO and D18:L8-BO are increased from 19.1 and 19.3% to 19.8 and 20.2%, respectively, which are among the highest values for single-junction OPVs. The university of B6Cl to increase the performance of OPVs is further evidenced in a range of polymer:NFA OPVs.

NIR-II Fluorescence Sensor Based on Steric Hindrance Regulated Molecular Packing for In Vivo Epilepsy Visualization.

Fluorescence sensing is crucial to study biological processes and diagnose diseases, especially in the second near-infrared (NIR-II) window with reduces background signals. However, it's still a great challenge to construct "off-on" sensors when the sensing wavelength extends into the second near-infrared (NIR-II) region to obtain higher imaging contrast, mainly due to the difficult synthesis of spectral overlapped quencher. Here, we present a new fluorescence quenching strategy, which utilizes steric hindrance quenchers (SHQ) to tune the molecular packing state of fluorophores and suppress the emission signal. Density functional theory (DFT) calculations further reveal that large SHQ can competitively packing with fluorophores and prevent their self-aggregation. Based on this quenching mechanism, a novel activatable "off-on" sensing method is achieved via bio-analyte responsive invalidation of SHQ, namely Steric Hindrance Invalidation geNerated Emission (SHINE) strategy.As a proof of concept, the ClO- sensitive SHQ lead to the bright NIR-II signal release in epileptic mouse hippocampus under the skull and high photon scattering brain tissue, providing the real-time visualization of ClO- generation process in living epileptic mice.