Backbone Packing Research Articles

Non-fused polymerized small-molecular acceptors containing thieno[3,4-c]pyrrole-4,6-dione core for all-polymer solar cells

The innovation of polymer acceptors through the polymerized small molecular acceptors (PSMAs) strategy has promoted the rapid development of all-polymer solar cells (all-PSCs) in recent years. However, the non-fused PSMAs have been rarely investigated compared with the fused-ring non-fullerene counterpart. In this work, we reported the synthesis of non-fused PSMAs with thieno[3,4-c]pyrrole-4,6-dione (TPD) core, exhibiting planar configuration, simplified synthesis, and near-infrared absorption. Two PSMAs with regiorandom or regioregular structures were prepared based on the TPD core, in which all-PSCs offered efficiencies of 4.00% for the regiorandom polymer and 10.99% for the regioregular polymer, respectively, which is among the highest performance for non-fused PSMAs. Further morphological and electrical characterizations unveiled that higher device performance of regioregular TPD-based PSMAs was due to the efficient exciton separation and charge transport with more ordered backbone packing in the solid state. This work demonstrates that the TPD unit is a promising building block for the construction of PSMA polymers, providing more selections for the design of high-performance all-PSCs.

D−π−A Strategy to boost dielectric breakdown strength of polyimide insulation

Polyimide (PI) possesses multiple advantages including excellent thermal stability, mechanical property and chemical resistance, which has been considered as one of the promising candidates for high-performance electrical insulation materials. Optimizing the polymer structure such as extending the band gap can yield high intrinsic breakdown strength, attributed to the inhibition of impact ionization. However, in most cases, large band gap is achieved at the cost of reducing the backbone coplanarity and rigidity or the intermolecular interaction, resulting in undesirable thermal and mechanical performance. Herein, we introduce an effective strategy to produce thermally stable and mechanically strong polyimide insulation with high breakdown strength through introducing aromatic donor groups into the main chains to construct a D−π−A structure. On the one hand, the formation of D−A effect increases the materials polarization and enhances dipole-induced scattering. On the other hand, enhanced intermolecular interaction via π−π stacking decreases free volume in PIs. Then, increased conjugation degree of the backbone and high packing density between the polymer chains benefit to thermal stability and mechanical properties. Based on this strategy, N-arkyl carbazole groups are preferred, in which the soft alkyl side groups can occupy the pores between the polymer chains to further decrease free volume. As a result, we afford polyimide insulation with significantly improved breakdown strength from 291 kV mm−1 to 570−632 kV mm−1, as compared to the reference PI ODA-PMDA. Simultaneously, the resultant PIs, such as PI-Bu, preserve high Td5% above 524 ℃, high Tg above 364 ℃ and tensile strength above 80 MPa.

Backbone coplanarity manipulation via hydrogen bonding to boost the n-type performance of polymeric mixed conductors operating in aqueous electrolyte.

The development of high-performance n-type semiconducting polymers remains a significant challenge. Reported here is the construction of a coplanar backbone via intramolecular hydrogen bonds to dramatically enhance the performance of n-type polymeric mixed conductors operating in aqueous electrolyte. Specifically, glycolated naphthalene tetracarboxylicdiimide (gNDI) couples with vinylene and thiophene to give gNDI-V and gNDI-T, respectively. The hydrogen bonding functionalities are fused to the backbone to ensure a more coplanar backbone and much tighter π-π stacking of gNDI-V than gNDI-T, which is evidenced by density functional theory simulations and grazing-incidence wide-angle X-ray scattering. Importantly, these copolymers are fabricated as the active layer of the aqueous-based electrochromic devices and organic electrochemical transistors (OECTs). gNDI-V exhibits a larger electrochromic contrast (ΔT = 30%) and a higher coloration efficiency (1988 cm2 C-1) than gNDI-T owing to its more efficient ionic-electronic coupling. Moreover, gNDI-V gives the highest electron mobility (0.014 cm2 V-1 s-1) and μC* (2.31 FV-1 cm-1 s-1) reported to date for NDI-based copolymers in OECTs, attributed to the improved thin-film crystallinity and molecular packing promoted by hydrogen bonds. Overall, this work marks a remarkable advance in the n-type polymeric mixed conductors and the hydrogen bond functionalization strategy opens up an avenue to access desirable performance metrics for aqueous-based electrochemical devices.

Cooperativity and fragility in furan-based polyesters with different glycolic subunits as compared to their terephthalic counterparts

This works aims to investigate the effect of the molecular groups found in polyester backbones (type of ring in the acidic subunit and length of the glycolic subunit) on the molecular dynamics. The investigation is done on three furan-based polyesters (PEF, PPF and PBF) as compared to their terephthalic counterparts (PET, PTT, and PBT) after full quenching from the molten state. The segmental molecular dynamics is investigated with MT-DSC, FSC and DRS. It is shown that the cooperativity decreases as the length of the glycolic subunit increases in both furan-based and terephthalic polyesters. No direct correlation between the fragility index and the cooperativity is observed in furan-based polyesters containing glycolic subunits of different lengths. The differences in the isochoric fragilities obtained for the furan-based polyesters and their terephthalic counterparts has been assumed to result from the combination of backbone flexibility and packing efficiency of the macromolecular chains in the amorphous phase.

Donor Functionalization Tuning the N‐Type Performance of Donor–Acceptor Copolymers for Aqueous‐Based Electrochemical Devices

AbstractIn this work, three n‐type donor–acceptor copolymers consisting of glycolated naphthalene tetracarboxylicdiimide (gNDI) coupled with variable donating companion moieties are reported. Using 2,2′‐bis(3,4‐ethylenedioxy)bithiophene, 2,​2′‐​bithiophene, 3,3′‐difluoro‐2,2′‐bithiophene (FBT), the donating strength of the donor units is systematically functionalized. These copolymers are used as a platform for aqueous‐based electrochemical devices, including energy‐storage devices, electrochromic devices (ECDs), and organic electrochemical transistors (OECTs). It is found that the electrochemical redox stability and electron mobility of copolymers are significantly improved via weakening the electron‐donating strength of donor units. gNDI coupling with FBT (gNDI‐FBT) exhibits a charge‐storage capacity exceeding 190 Fg−1, which is the highest value reported to date for NDI‐based polymer electrodes in aqueous media. For ECDs, gNDI‐FBT remains 100% of initial electrochromism contrast (∆%T = 20%) up to 1200 s. In addition, gNDI‐FBT outperforms its two analogs in OECTs, including lower threshold voltage (0.19 V), faster response time (45.5 ms), and higher volumetric capacitance (197 F cm−3). Moreover, gNDI‐FBT with fluorine atoms leads to the bipolarons delocalization along the polymer backbone and favorable molecular packing for ion–electron transport. Through such weak donor functionalization strategy, this work provides ways for n‐type copolymers tuning to access desirable performance metrics in optical, electrochemical, and bioelectronic applications.

A simple high-performance fully nonfused ring electron acceptor with a planar molecular backbone

We designed two simple fully nonfused ring electron acceptors 4T-OEH and 4T-EH with 3,4-bis(alkoxy)thiophene and 3,4-dialkylthiophene π-bridge units, respectively, which can be modularly synthesized with only four high-yield steps. With the help of intramolecular S-O noncovalent interaction, 4T-OEH tends to form a planar molecular backbone, which is beneficial for the electron delocalization and charge transport. Besides, the neat 4T-OEH film displays a more ordered molecular packing and obviously red-shifted absorption after thermal annealing. Compared with 4T-EH, 4T-OEH based devices can form more homogenous phase morphology, higher and more balanced hole and electron mobilities. The optimal OSCs based on 4T-OEH can generate an excellent PCE of 12.12%, which is much higher than 4T-OEH based ones (7.36%). It is worth noting that the figure-of-merit values of 4T-OEH is much higher than the star acceptors (ITIC and Y6), demonstrating its high potential for future practical application. Our work has demonstrated that we can tune the backbone planarity, solubility and packing behavior of acceptor molecules via optimizing their lateral substituents to obtain high efficiency and low-cost fully nonfused ring electron acceptors.

High‐Performance n‐Type Organic Electrochemical Transistors Enabled by Aqueous Solution Processing of Amphiphilicity‐Driven Polymer Assembly

AbstractDespite the growing attention on organic electrochemical transistors (OECTs), most research has focused on the design of p‐type active materials, and the number of high‐performance n‐type materials is limited. Herein, a series of naphthalene diimide‐based polymers incorporated with asymmetrically branched oligo(ethylene glycol) (OEG) side chains are developed to enable green‐solvent‐processed, high‐performance n‐type OECTs. The branched OEG side chains afford sufficient solubility in eco‐friendly ethanol/water solvent mixtures. Importantly, taking advantage of the amphiphilic nature of OEG‐based polymers, ethanol/water solvents selectively solvate hydrophilic OEG side chains, while producing assembled π−π stacks of hydrophobic backbones. This enables highly ordered polymer packing with a preferential edge‐on orientation, and thus excellent lateral charge transport. In particular, the fine‐tuned OEG side chains of P(NDIMTEG‐T) provide compact backbone packing, effective polaron generation, and superior electrochemical stability with optimized swelling capability. The resultant n‐type OECT shows the best electrical/electrochemical performance in the family, represented by a high transconductance (gm) of 0.38 S cm−1 and a large figure‐of‐merit (µC*) of 0.56 F V−1 cm−1 s−1. This study demonstrates the use of aqueous processing in OECTs, for the first time, and suggests important guidelines for the design of n‐type organic mixed ionic‐electronic conductors with excellent OECT characteristics.

An online GPCR structure analysis platform.

We present an online, interactive platform for comparative analysis of all available G-protein coupled receptor (GPCR) structures while correlating to functional data. The comprehensive platform encompasses structure similarity, secondary structure, protein backbone packing and movement, residue-residue contact networks, amino acid properties and prospective design of experimental mutagenesis studies. This lets any researcher tap the potential of sophisticated structural analyses enabling a plethora of basic and applied receptor research studies.

Effective Modulation of Exciton Binding Energies in Polymorphs of a Small-Molecule Acceptor for Organic Photovoltaics.

The operation mechanisms and energy losses for organic solar cells are essentially determined by the exciton binding energies (Eb) of organic active materials. Because the factor of chemical modifications is precluded, polymorphisms featuring different packing motifs of the same molecular structures provide an ideal platform for revealing the influence of solid-state packing. Herein, we have calculated the Eb values in three different cystal phases of a representative acceptor-donor-acceptor molecular acceptor (IDIC) by the self-consistent quantum mechanics/embedded charge approach. The results show that the differences of mere molecular packing modes can result in a substantial change in Eb of ≤50%, in the range of 0.21-0.34 eV among the three IDIC crystal phases. Moreover, a higher backbone packing dimensionality is found to be beneficial for obtaining a smaller Eb. This indicates that polymorph engineering is an effective way to reduce Eb toward low-energy-loss organic solar cells.

Printing 2D Conjugated Polymer Monolayers and Their Distinct Electronic Properties

AbstractRecently, 2D monolayer films of conjugated polymers have gained increasing attention owing to the preeminence of 2D inorganic films that exhibit unique optoelectronic and mechanical properties compared to their bulk analogs. Despite numerous efforts, crystallization of semiconducting polymers into highly ordered 2D monolayer films still remains challenging. Herein, a dynamic‐template‐assisted meniscus‐guided coating is utilized to fabricate continuous, highly ordered 2D monolayer films of conjugated polymers over a centimeter scale with enhanced backbone π–π stacking. In contrast, monolayer films printed on solid substrates confer upon the 1D fiber networks strong alkyl side‐chain stacking at the expense of backbone packing. From single‐layers to multilayers, the polymer π‐stacks change from edge‐on to bimodal orientation as the film thickness reaches ≈20 nm. Spectroscopic and cyclic voltammetry analysis reveals an abrupt increase in J‐aggregation and absorption coefficient and a decrease in bandgap and highest occupied molecular orbital level until critical thickness, possibly arising from the straightened polymer backbone. This is corroborated by an abrupt increase in hole mobility with film thickness, reaching a maximum of 0.7 cm2 V−1 s−1 near the critical thickness. Finally, fabrication of chemical sensors incorporating polymer films of various thicknesses is demonstrated, and an ultrahigh sensitivity of the ≈7 nm thick ultrathin film (bilayers) to 1 ppb ammonia is shown.

Blend anion exchange membranes containing polymer of intrinsic microporosity for fuel cell application

High hydroxide conductivity and alkali resistance of anion exchange membranes (AEMs) is the basic requirement for realizing the practical application of anion exchange membrane fuel cells. In this work, we develop a novel blend AEM incorporating polymer of intrinsic microporosity (PIM). PIM features highly rigid backbone and loose packing so that the resultant blend AEM containing PIM possesses increased free volume so that the ion clusters formed by microphase separation may get easily percolated and form pathways for hydroxide ion transport. The blend AEM containing 30% PIM shows a low ion exchange capacity (IEC) of 0.77 mmol g−1, but a relatively high conductivity of 16.9 mS cm−1 at 30 °C, and yields a H2/O2 fuel cell power density of 163 mW cm−2 at 60 °C. The membrane also shows a high mechanical robustness (tensile strength 43 MPa) and alkaline stability as compared with that without PIM incorporation. To the best of our knowledge, this work is the first report of PIM incorporation in blend AEM, and provides a new and effective strategy to promote hydroxide ion conduction in AEMs at relatively low IEC, which may pave the way to achieve better balanced conductivity and stability.

Impact of Incorporating Nitrogen Atoms in Naphthalenediimide-Based Polymer Acceptors on the Charge Generation, Device Performance, and Stability of All-Polymer Solar Cells.

Substitution of C atoms in a polymer backbone by N atoms allows for the facile tuning of the energy levels as well as the backbone conformation and packing structures of conjugated polymers. Herein, we report a series of three polymer acceptors (PAs) with N atoms introduced at different positions of the backbone and investigate how these N atoms affect the device performances of all-polymer solar cells (all-PSCs). The three PAs, namely, P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz), are composed of naphthalenediimide (NDI)-based and benzothiadiazole (BT)-based derivatives (dithiophene-BT (BTT), dithiophene-thiadiazolepyridine (PTT), and dithiazole-BT (BTTz)). The PTT and BTTz units are synthesized by replacing the C atoms in BT and thiophene, respectively, with N atoms, which effectively tune the optical, electrochemical, and charge-transporting properties of the corresponding PAs. The all-PSCs using poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl))benzo[1,2-b:4,5-b']dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione)] (PBDB-T) as a polymer donor and P(NDI2DT-PTT) as PA exhibit a significantly enhanced power conversion efficiency (PCE) of 6.95%, whereas the all-PSCs based on the other PAs show relatively lower PCEs (6.02% for PBDB-T:P(NDI2DT-BTT) and 1.43% for PBDB-T:P(NDI2DT-BTTz)). The high PCE of the PBDB-T:P(NDI2DT-PTT) device is due to the superior charge transfer and charge dissociation, resulting from the closely matched energy levels between PBDB-T and P(NDI2DT-PTT), as well as a more favorable bulk heterojunction morphology with improved miscibility. Importantly, the P(NDI2DT-PTT)-based all-PSC device shows improved air stability compared to the P(NDI2DT-BTT)-based device, which is most likely due to a decreased lowest unoccupied molecular orbital level of the PA. Our findings suggest that the incorporation of N atoms into the PAs is an effective strategy for improving the efficiency and stability of all-PSCs.

Molecular Structure of Aromatic Reverse Osmosis Polyamide Barrier Layers.

The molecular structures of polyamide barrier layers in reverse osmosis membranes, made by interfacial polymerization of m-phenylenediamine and trimesoyl chloride under different reaction and post-treatment conditions, were characterized by grazing incidence wide-angle X-ray scattering (GIWAXS). The molecular backbone packing is consistent with two different aromatic molecular packing motifs (parallel and perpendicular) with preferential surface-induced orientation. The results suggest that the perpendicular, T-shaped, packing motif (5 Å spacing) might be associated with optimal membrane permeance, compared with the parallel packings (3.5-4.0 Å spacings).

Structural attributes of mammalian prion infectivity: Insights from studies with synthetic prions

Prion diseases are neurodegenerative disorders that affect many mammalian species. Mammalian prion proteins (PrPs) can misfold into many different aggregates. However, only a small subpopulation of these structures is infectious. One of the major unresolved questions in prion research is identifying which specific structural features of these misfolded protein aggregates are important for prion infectivity in vivo Previously, two types of proteinase K-resistant, self-propagating aggregates were generated from the recombinant mouse prion protein in the presence of identical cofactors. Although these two aggregates appear biochemically very similar, they have dramatically different biological properties, with one of them being highly infectious and the other one lacking any infectivity. Here, we used several MS-based structural methods, including hydrogen-deuterium exchange and hydroxyl radical footprinting, to gain insight into the nature of structural differences between these two PrP aggregate types. Our experiments revealed a number of specific differences in the structure of infectious and noninfectious aggregates, both at the level of the polypeptide backbone and quaternary packing arrangement. In particular, we observed that a high degree of order and stability of β-sheet structure within the entire region between residues ∼89 and 227 is a primary attribute of infectious PrP aggregates examined in this study. By contrast, noninfectious PrP aggregates are characterized by markedly less ordered structure up to residue ∼167. The structural constraints reported here should facilitate development of experimentally based high-resolution structural models of infectiosus mammalian prions.

TetraBASE: A Side Chain-Independent Statistical Energy for Designing Realistically Packed Protein Backbones.

To construct backbone structures of high designability is a primary aspect of computational protein design. We report here a side chain-independent statistical energy that aims at realistic modeling of through-space packing of polypeptide backbones. To mitigate the lack of explicit amino acid side chains, the model treats the interbackbone site packing as being dependent on peptide local conformation. In addition, new variables suitable for statistical analysis, one for relative orientation and another for distance, have been introduced to represent the intersite geometry based on the asymmetrical tetrahedron organization of distinct chemical groups surrounding the Cα-carbon atoms. The resulting tetrahedron-based backbone statistical energy (tetraBASE) model has been used to optimize the tertiary organizations of secondary structure elements (SSEs) of designated types with Monte Caro simulated annealing, starting from artificial initial configurations. The tetraBASE minimum energy structures can reproduce SSE packing frequently observed in native proteins with atomic root-mean-square deviations of 1-2 Å. The model has also been tested by examining the stability of native SSE arrangements under tetraBASE. The results suggest that tetraBASE model can be used to effectively represent interbackbone packing when designing backbone structures without explicitly knowing side chain types.

Improvising 5-HT7R homology model for design of high affinity ligands: model validation with docking, embrace minimization, MM-GBSA, and molecular dynamic simulations

The subtype, 5-HT7R has been implicated in neurological disorders and presents itself as a promising target for antidepressant drugs. Design of targeted selective ligands, require a sound knowledge of 3D-receptor structure. In absence of receptor structure, structure-based design of targeted ligands relies on generation of 5-HT7R homology model. In this study, the impact of template choice, alignment, and model building methods on the homology model of 5-HT7R is addressed. The compactness and model quality due to the presence of cholesterol (lipidic receptor) have also been observed. The results suggest good stereochemical quality of the final model. Ramachandran Plot Analysis indicated more than 97.5% amino acid residues in the favorable region. The overall quality factor was 91.8% using ERRAT. The Z-score for backbone confirmation and packing quality were −1.248 and −1.427, respectively, using WHATCHECK. The RMS Z-score for side chain planarity was .711. Other validation results for the final model include binding site analysis in which Asp162, Val163, Phe343, Phe344, Arg350, Arg367, and Leu370 conserved residues were found in the active site, correlation coefficient of .82 in ligand-based screening and .85 in embrace minimization. Further, the model showed good correlation for agonist and antagonist in docking ( ≈ .76, ≈ .82), embrace minimization ( ≈ .73, ≈ .72), and MM-GBSA ( ≈ .69, ≈ .75) studies. The model was subjected to Molecular Dynamics (MD) simulation of 20 ns both in ligand-free and ligand-bound receptor (agonist and antagonist) system in order to assess its stability.

Mesoscale Ordering and Charge-Transport of Crystalline Spiro-OMeTAD Organic Semiconductors

The mesoscale ordering and charge-transport of crystalline spiro-OMeTAD, a hole-transporting material extensively used in perosvkite and dye-sensitized solar cell applications, were explored using molecular dynamics and hole mobility calculations. Morphologies were evaluated through conformational changes, nematic order and paracrystallinity at various temperatures. Charge transport is predicted with electronic structure methods employing a hopping mechanism. Our calculations show that along with strong fluorene backbone packing, phenylenes in the methoxyphenyl–amine substituents of spiro-OMeTAD are an integral part of the material performance. Backbone and substituent paracrystallinity predictions showed highly ordered crystalline phase. The methoxyphenyl substituents have multiple conformations in the unit-cell scale, but interphenylene electronic-coupling remain nearly constant. A thermal increase in positional disorder results in a systematic increase in energetic disorder and a decrease in hole mobil...

An In Situ Investigation into the Formation of the Solvent‐Induced Crystalline Phase of Poly(9,9‐Dioctylfluorene) in Solvent Vapor Annealing

A new metastable solvent‐induced clathrate liquid crystalline phase of β phase (named β' here) in crystalline poly(9,9‐dioctylfluorene) (PFO) thin film induced by solvent annealing is found by a combination of in situ ultraviolet and visible spectrophotometry (UV‐vis), photoluminescence spectroscopy (PL), and grazing incidence wide‐angle X‐ray scattering (GIWAXS). The solvent annealing process consists of three processes: diffusion of solvent molecules into the film; saturation of solvent in the film; and drying of the film under nitrogen. The formation of β' phase with ordered packing of side chains and disordered packing of backbones occurs during the diffusion process of solvent molecules into the film. When the solvent molecules penetrate the film, the disordered side chains start to align themselves to form an ordered structure, and the ordering would gradually in the saturationprocess. Furthermore, the ordering of side chains drives an ordered rearrangement of the backbones during the drying process; however, the crystallinity of the side chains decreases with the orderly rearrangement of backbones due to the helical conformation of PFO. image

Necessity of high-resolution for coarse-grained modeling of flexible proteins.

The popular MARTINI coarse-grained (CG) force field requires the protein structure to be fixed, and is unsuitable for simulating dynamic processes such as protein folding. Here, we examine the feasibility of developing a flexible protein model within the MARTINI framework. The results demonstrate that the MARTINI CG scheme does not properly describe the volume and packing of protein backbone and side chains and leads to excessive collapse without structural restraints in explicit CG water. Combining atomistic protein representation with the MARTINI CG solvent, such as in the PACE model, dramatically improves description of flexible protein conformations. Yet, the CG solvent is insufficient to capture the conformational dependence of protein-solvent interactions, and PACE is unable to properly model context dependent conformational transitions. Taken together, high physical resolution at or near the atomistic level is likely necessary for flexible protein models with explicit, microscopic solvents, and the coarse-graining needs to focus on possible simplification in interaction potentials. © 2016 Wiley Periodicals, Inc.

Effect of Induced Self-Organization in Mixtures of Amphiphilic Macromolecules with Different Stiffness

Effect of induced self-organization and liquid-crystal ordering of disordered globules of flexible amphiphilic macromolecules was observed in 1:1 mixtures of flexible and stiff helical macromolecules of similar composition. Mixtures of fully flexible macromolecules and helical macromolecules with various stiffness of backbone were studied by means of molecular dynamics simulation. It was found that if the local helical structure of the backbone is stiff enough to induce formation of aggregates with helical packing of backbone in poor solvent, the helical and flexible macromolecules segregate upon worsening of solvent quality. In dilute solution the flexible macromolecules are compacted into single globules with hydrophobic core and hydrophilic shell. The macromolecules with stiff local helical structure form aggregates of few helical chains. The aggregates have a core composed by intertwined backbones which is surrounded by a hydrophilic outer shell consisting of side groups. Increase of volume fraction o...