Asymmetric Core Research Articles

A Noncovalently Fused‐Ring Asymmetric Electron Acceptor Enables Efficient Organic Solar Cells

Main observation and conclusionRecently, the asymmetric nonfullerene acceptors (NFAs) with acceptor‐donor‐acceptor (A‐D‐A) structure have been developed rapidly, especially for the modification of asymmetric core, asymmetric side chains and asymmetric end groups. In this work, a novel asymmetric A‐D‐π‐A type NFA with a noncovalently fused‐ring core named PIST‐4F is synthesized, containing an indacenodithieno[3,2‐b]dithiophene (IDT), two strong electron‐withdrawing end groups and an alkylthio‐substituted thiophene π‐bridge. Benefiting from the S···S noncovalent interaction between the sulfur atom on π‐bridge and the adjacent thiophene in IDT, the PIST‐4F presents nearly planar geometry and extended conjugated area, resulting in the optimized electronic properties, charge transport, and film morphology compared to the symmetric NFA PI‐4F. As a result, PM6:PIST‐4F‐based devices achieve a higher power conversion efficiency (PCE) of 13.8%, while the PM6:PI‐4F‐based devices only show a PCE of 7.1%. Notably, the PM6:PIST‐4F‐based devices processed with nonhalogen solvent toluene exhibit an excellent PCE as high as 13.1%. These results indicate that PIST‐4F is an effective acceptor for high‐efficiency organic solar cells.

Construction of Highly Proton-Conductive Zr(IV)-Based Metal-Organic Frameworks From Pyrrolo-pyrrole-Based Linkers with a Rhombic Shape.

To date, numerous zirconium cluster-based metal-organic frameworks (Zr-MOFs) with attractive physical properties have been achieved thanks to tailorable organic linkers and versatile Zr clusters. Nevertheless, in comparison with the most-used high-symmetry organic linkers, low-symmetry linkers have rarely been exploited in the construction of Zr-MOFs. Despite challenges in predicting the structure and topology of the MOF, linker desymmetrization presents opportunities for the design of Zr-MOFs with unusual topologies and unexpected functionalities. Herein, we report for the first time the construction of two robust Zr-MOFs (IAM-7 and IAM-8) from two pyrrolo-pyrrole-based low-symmetry tetracarboxylate linkers with a rare rhombic shape. The low symmetry of the linkers arises from the asymmetric pyrrolo-pyrrole core and the varying branch lengths, which play a critical role in the structural diversity between IAM-7 and IAM-8 seen from the structural analysis and lead to hydrophilic channels that contain uncoordinated carboxylate groups in the structure of IAM-7. Furthermore, the proton conductivity of IAM-7 displays a high temperature and humidity dependence where the proton conductivity increases from 2.84 × 10-8 S cm-1 at 30 °C and 40% relative humidity (RH) to 1.42 × 10-2 S cm-1 at 90 °C and 95% RH, making it among one of the most conductive Zr-MOFs. This work not only enriches the library of Zr-MOFs but also offers a platform for the design of low-symmetry linkers toward the structural diversity or irregularity of MOFs as well as their structure-related properties.

High-Performance Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors Enabled by Asymmetric Cores with Enhanced Noncovalent Intramolecular Interactions.

Nonfullerene acceptors (MQ3, MQ5, MQ6) are synthesized using asymmetric and symmetric ladder-type heteroheptacene cores with selenophene heterocycles. Although MQ3 and MQ5 are constructed with the same number of selenophene heterocycles, the heteroheptacene core of MQ5 is end-capped with selenophene rings while that of MQ3 is flanked with thiophene rings. With the enhanced noncovalent interaction of O⋅⋅⋅Se compared to that of O⋅⋅⋅S, MQ5 shows a bathochromically shifted absorption band and greatly improved carrier transport, leading to a higher power conversion efficiency (PCE) of 15.64 % compared to MQ3, which shows a PCE of 13.51 %. Based on the asymmetric heteroheptacene core, MQ6 shows an improved carrier transport induced by the reduced π-π stacking distance, related with the increased dipole moment in comparison with the nonfullerene acceptors based on symmetric cores. MQ6 exhibits a PCE of 16.39 % with a VOC of 0.88 V, a FF of 75.66 %, and a JSC of 24.62 mA cm-2 .

High‐Performance Ladder‐Type Heteroheptacene‐Based Nonfullerene Acceptors Enabled by Asymmetric Cores with Enhanced Noncovalent Intramolecular Interactions

AbstractNonfullerene acceptors (MQ3, MQ5, MQ6) are synthesized using asymmetric and symmetric ladder‐type heteroheptacene cores with selenophene heterocycles. Although MQ3 and MQ5 are constructed with the same number of selenophene heterocycles, the heteroheptacene core of MQ5 is end‐capped with selenophene rings while that of MQ3 is flanked with thiophene rings. With the enhanced noncovalent interaction of O⋅⋅⋅Se compared to that of O⋅⋅⋅S, MQ5 shows a bathochromically shifted absorption band and greatly improved carrier transport, leading to a higher power conversion efficiency (PCE) of 15.64 % compared to MQ3, which shows a PCE of 13.51 %. Based on the asymmetric heteroheptacene core, MQ6 shows an improved carrier transport induced by the reduced π–π stacking distance, related with the increased dipole moment in comparison with the nonfullerene acceptors based on symmetric cores. MQ6 exhibits a PCE of 16.39 % with a VOC of 0.88 V, a FF of 75.66 %, and a JSC of 24.62 mA cm−2.

Toward quantitative electronic structure in small gold nanoclusters.

Ligand-protected gold nanoclusters (AuNCs) feature a dense but finite electronic structure that can be rationalized using qualitative descriptions such as the well-known superatomic model and predicted using quantum chemical calculations. However, the lack of well-resolved experimental probes of a AuNC electronic structure has made the task of evaluating the accuracy of electronic structure descriptions challenging. We compare electronic absorption spectra computed using time-dependent density functional theory to recently collected high resolution experimental spectra of Au9(PPh3)8 3+ and Au8(PPh3)7 2+ AuNCs with strikingly similar features. After applying a simple scaling correction, the computed spectrum of Au8(PPh3)7 2+ yields a suitable match, allowing us to assign low-energy metal-metal transitions in the experimental spectrum. No similar match is obtained after following the same procedure for two previously reported isomers for Au9(PPh3)8 3+, suggesting either a deficiency in the calculations or the presence of an additional isomer. Instead, we propose assignments for Au9(PPh3)8 3+ based off of similarities Au8(PPh3)7 2+. We further model these clusters using a simple particle-in-a-box analysis for an asymmetrical ellipsoidal superatomic core, which allows us to reproduce the same transitions and extract an effective core size and shape that agrees well with that expected from crystal structures. This suggests that the superatomic model, which is typically employed to explain the qualitative features of nanocluster electronic structures, remains valid even for small AuNCs with highly aspherical cores.

Asymmetrical anterior thigh muscle atrophy as an atypical presentation of RYR1-core myopathy

•RYR1 variants can manifest in adult life mainly with asymmetrical core myopathy. •Asymmetrical anterior thigh muscle atrophy and core myopathy are distinctive features in RYR1 pathogenic variants. •Muscle MRI images revealed a marked asymmetrical involvement of the left quadriceps with a disto-proximal gradient.

Fluorine functionalized asymmetric indo [2,3-b]quinoxaline framework based D-A copolymer for fullerene polymer solar cells

Innovating molecular structure of copolymer donor materials is still one of the prominent approach to obtain high-performance polymer solar cells (PSCs). In this paper, two novel wide bandgap (WBG) copolymers, namely PBDTTS-IQ and PBDTTS-DFIQ, based on asymmetric planar aromatic core indo [( Li et al., 2012; Wang et al., 2020) 2,32,3-b]quinoxaline (IQ) as acceptor unit through tuning side chains with fluorine (F) atom engineering and exemplary alkylthio-thienyl substituted benzodithiophene (BDTTS) donor group, are synthesized and finally employed as the photovoltaic donor materials for fullerene polymer solar cells (PSCs). After blending with PC 71 BM acceptor, the PBDTTS-DFIQ:PC 71 BM blend film presented better efficient exciton dissociation and charge extraction, more balanced electron/hole mobility ( μ h / μ e ), and nice morphology in comparison with PBDTTS-IQ:PC 71 BM blend film. Encouragingly, the PBDTTS-DFIQ:PC 71 BM based PSCs exhibits a higher power conversion efficiency (PCE) of 7.4% than that of the device based on the PBDTTS-IQ:PC 71 BM blend with a PCE of 4.96%, which thanks to an enhancement of open-circuit voltage ( V oc ) of 0.84 V, short current density ( J sc ) of 13.26 mA cm −2 and fill factor (FF) of 66.00% simultaneously. These results demonstrate that this asymmetric IQ framework is a wonderful acceptor moiety to build light-harvesting copolymers for highly efficient PSCs. Two novel NBG D-A copolymers, namely PBDTTS-IQ and PBDTTS-DFIQ, based on asymmetric indo [2,3-b]quinoxaline (IQ) unit as acceptor unit through tuning the side chains with halogen atom fluorine (F) engineering, aiming to achieve novel copolymer donors with good photovoltaic performance. • Both narrow bandgap copolymers were developed based on asymmetric planar aromatic backbone indo [2,3-b]quinoxaline as an acceptor unit. • The fluorinated PBDTTS-DFIQ exhibits a lower HOMO energy level, better planarity and higher dipole moment in comparison with PBDTTS-IQ. • The PBDTTS-DFIQ:PC 71 BM-based device presents a maximum PCE of 7.40%. • Fluorinated asymmetric indo [2,3-b]quinoxaline framework is a wonderful acceptor moiety to build light-harvesting copolymers for efficient PSCs.

Asymmetric Core-Shell Gold Nanoparticles and Controllable Assemblies for SERS Ratiometric Detection of MicroRNA.

Janus nanogap gold nanoparticles (JAuNNPs) with varying proportions of Au shell coverage of (ca. 100/75/50/25 %) are presented. The internal nanogap between the partial Au shell and core caused asymmetric optical behavior; tunability depends on the degree of Au shell coverage and structural asymmetry. The shell-to-shell or core-to-core JAuNNDs(50 %) were self-assembled from amphiphilic JAuNNPs(50 %) by tuning the hydrophilic and hydrophobic polymer brushes on the Au core or shell. The positions of electromagnetic field enhancement of JAuNNDs varied with geometrical configurations because of hybridized plasmonic coupling effects. Furthermore, DNA linkers were utilized to form JAuNND12 (50 %). By combining with Raman molecules, ratiometric SERS signals could be generated, enabling JAuNND12 (50 %) to image the distribution of miR-21 in living cells and tumors. Asymmetric JAuNNPs allowed facile conjugation of various linkage molecules to fabricate dimeric nanostructures.

Asymmetric Core–Shell Gold Nanoparticles and Controllable Assemblies for SERS Ratiometric Detection of MicroRNA

AbstractJanus nanogap gold nanoparticles (JAuNNPs) with varying proportions of Au shell coverage of (ca. 100/75/50/25 %) are presented. The internal nanogap between the partial Au shell and core caused asymmetric optical behavior; tunability depends on the degree of Au shell coverage and structural asymmetry. The shell‐to‐shell or core‐to‐core JAuNNDs(50 %) were self‐assembled from amphiphilic JAuNNPs(50 %) by tuning the hydrophilic and hydrophobic polymer brushes on the Au core or shell. The positions of electromagnetic field enhancement of JAuNNDs varied with geometrical configurations because of hybridized plasmonic coupling effects. Furthermore, DNA linkers were utilized to form JAuNND12(50 %). By combining with Raman molecules, ratiometric SERS signals could be generated, enabling JAuNND12(50 %) to image the distribution of miR‐21 in living cells and tumors. Asymmetric JAuNNPs allowed facile conjugation of various linkage molecules to fabricate dimeric nanostructures.

Asymmetric Colloidal Particles Fabricated by Polymerization-Induced Surface Self-Assembly Approach

In the past decades, the synthesis of asymmetric colloidal particles has been of wide concern in material science because of their anisotropic morphologies and unique properties. However, the synthesis of the asymmetric particles with controllable anisotropy still remains a big challenge because of the lack of effective methods. In this research, polymerization-induced surface self-assembly (PISSA) approach was demonstrated to be an effective method in the synthesis of colloidal particles with tunable asymmetric core–shell structures. Reversible addition–fragmentation chain transfer agents were covalently anchored onto the surfaces of silica particles and coupled onto the ends of methoxy polyethylene glycol (PEG) chains, leading to the synthesis of CTA-modified silica particles (SiO2-CTA) and PEG macro-CTA agents (PEG-CTA), respectively. PISSA process was conducted by using SiO2-CTA and PEG-CTA as co-RAFT agents in RAFT dispersion polymerization of styrene. In the RAFT polymerizations, polymer layers with PS nodules were formed on the surfaces of SiO2 particles. It was demonstrated that the formation of the nodules was related to the production of the PS homopolymer in the PISSA process. In order to control the asymmetric surface structures, RAFT dispersion polymerizations of styrene with added “free” RAFT agents were performed, and it turned out that the eccentrically positioned core–shell structures with silica cores and polymer layers were prepared. The colloidal particles experience morphology changes from surface nodules to snowman-like structures and finally to asymmetric spherical structures, depending on the monomer conversion and the feeding ratio of the co-RAFT agents. Kinetics studies were performed to investigate the mechanism of the formation of the asymmetric particles. After etching the silica cores with HF solution, asymmetric hollow capsules were fabricated.

Torque ripple reduction of synchronous reluctance machine by using asymmetrical barriers and hybrid magnetic core

As there is no need of permanent magnet (PM) material and only silicon steel sheet required on the rotor, synchronous reluctance machine (SynRM) can be used for many applications and draws a great research interest. For the SynRM, the torque ripple is a big issue and a great of work could been done on reducing it. In this paper, asymmetrical magnetic flux barriers in the SynRM rotor were studied comprehensively, including angle and width of each layer and each side of the magnetic barrier. The SynRMb with asymmetrical and parallel magnetic flux barrier was found as the best way to design SynRM based on the multi-objective design optimization method. Moreover, each parameter was studied to show the design rule of the asymmetrical magnetic flux barrier. As the average torque will be reduced with the asymmetrical barrier is used, the grain-oriented silicon steel is used on stator teeth of the SynRMb (SynRMbG) was proposed and studied. The analysis results show that the proposed new method can make the SynRM have better performance.

Backbone Engineering with Asymmetric Core to Finely Tune Phase Separation for High-Performance All-Small-Molecule Organic Solar Cells.

In order to obtain high-performance all-small-molecule organic solar cells (ASM-OSCs), it is crucial to exploit the available strategy for molecular design and to further understand key structure-property relationship that can rationally control the blend nanomorphology and influence the physical process. In this work, we design two small molecule donors FBD-S1 and TBD-S2 with identical electron-withdrawing units but various asymmetric central cores, which exhibit differing phase separation in Y6-based blend films. It is found that TBD-S2 with increased phase separation between donor and acceptor can lead to more favorable interpenetrating networks, effective exciton dissociation, and enhanced and more balanced charge transport. Importantly, a remarkable PCE of 13.1% is obtained for TBD-S2:Y6 based ASM-OSCs, which is an attractive photovoltaic performance for ASM-OSCs. This result demonstrates that the central core modification at the atomic level for small molecule donors can delicately control the phase separation and optimize photophysical processes, and refines device performance, which facilitate development in the ASM-OSC research field.

Highly birefringent slotted core photonic crystal fiber for terahertz waveguiding

A novel porous core photonic crystal fiber (PC-PCF) is suggested and analyzed for terahertz waveguiding. The PC-PCF has a TOPAS background material with suspended asymmetric slotted core. Therefore, high birefringence of 0.09 is achieved with small material absorption losses of 0.016 cm−1 and 0.028 cm−1 for the quasi transverse electric (TE) and quasi transverse magnetic (TM) modes, respectively at f = 1.5 THz. Additionally low bending losses of 2.63 × 10–24 cm−1 and 8.16 × 10–36 cm−1 are obtained for the quasi TE and quasi TM modes, respectively at 1.0 cm bending radius and f = 1.5 THz. Further, the PC-PCF has an ultra-flat low dispersion of 0.54 $$\pm$$ 0.08 ps/THz/cm and 0.94 $$\pm 0.1{ }$$ ps/THz/cm for the quasi TE and TM modes, respectively within the frequency range of 0.8–1.2 THz. Therefore, the reported SSCPCF has a strong potential for usage in the Terahertz regime.

Improved Peierls-Nabarro model for asymmetric nonplanar 1/2

The 1/2 < 11_0]{111} ordinary dislocations play an important role in the mechanical behaviors of L10 alloys. The core of this kind of dislocations has asymmetric four-fold nonplanar structure spreading onto two equivalent {111} planes, which makes the traditional planar core structure based Peierls-Nabarro (P–N) model inappropriate to describe the dislocation properties. Under this context, an improved Peierls-Nabarro (P–N) model is developed in the present work to investigate the dislocation width, stress field and Peierls stress of the ordinary 1/2 < 11_0]{111} screw dislocation in L10 alloys (TiAl, TiGa and CuAu). This extended P–N model considers the nonplanar core structure with physical information obtained by the density functional theory (DFT) simulations. By the variational method, the corresponding dislocation equation is solved. It is found that the dislocation width of the ordinary 1/2 < 11_0]{111} screw dislocation is as narrow as 0.5b. Compared to the results predicted for the planar core structure or the assumed Volterra dislocation, the long-range stress field induced by the real asymmetric four-fold core presents a clear rotation. When increasing the applied stress, the distribution of the Burgers vector along the four different core folds differs more and more from each other. When the applied stress attains a critical value (i.e., the Peierls stress), the dislocation core turns to be a planar structure and a fully discrete method is used to calculate the Peierls stress. Different from the original P–N model that underestimates the Peierls stress by several orders of magnitude, the Peierls stress predicted by the improved P–N model is well consistent with the previous DFT simulations. Apparently, when the long-range interaction between dislocations is taken into account for discrete dislocation simulations or theoretical analysis and when the Peierls stress is calculated for L10 alloys, the consideration of the asymmetric nonplanar core structure by the improved P–N model is necessary to have more accurate results.

Over 15% efficiency all-small-molecule organic solar cells enabled by a C-shaped small molecule donor with tailorable asymmetric backbone

Abstract In the past few years, compared with the rapid development of polymer solar cells (PSCs), the research progress of all-small-molecule organic solar cells (ASM-OSCs) lags far behind. Herein, two kinds of C-shaped SM donors named FBD-S3 and TBD-S4, bearing subtly tailorable asymmetric central core, are firstly reported. Both the two SMs show broad as well as matched absorption and energy level with classical acceptor Y6. The introduction of asymmetric core endows SM with Y6-similar bending skeleton and a unique network assembly in which the SM donor can easily interpenetrate into neighboring Y6 via strong intermolecular interaction and facile stacking direction. These features would hinder rapid aggregation and prevent to form large domains of single component in blends, resulting in an extraordinary power conversion efficiency of 15.10% in TBD-S4:Y6-based device, which is one of the highest values for ASM-OSCs. In addition, our comparative study demonstrates that although the donor material TBD-S4 exhibits reduced crystallinity, such a molecule matches better with acceptor Y6 and works more efficiently for ASM-OSCs. This work indicates that conformation tailorable by asymmetric central core is a novel and powerful method to design SM donor, which open a new avenue for highly efficient ASM-OSCs.

Asymmetric Host Molecule Bearing Pyridine Core for Highly Efficient Blue Thermally Activated Delayed Fluorescence OLEDs.

In this study, two host materials, pCzBzbCz and pCzPybCz, are synthesized to achieve a high efficiency and long lifetime of blue thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The molecular design strategy involves the introduction of a pyridine group into the core structure of pCzPybCz as an electron-withdrawing unit, and an electron-donating phenyl group into the structure of pCzBzbCz. These host materials demonstrate good thermal stability and high triplet energy (T1 =3.07 eV for pCzBzbCz and 3.06 eV for pCzPybCz) for the fabrication of blue TADF-OLEDs. In particular, pCzPybCz-based OLED devices demonstrate an external quantum efficiency (EQE) of 22.7 % and an operational lifetime of 24 h (LT90 , time to attain 90 % of initial luminance) at an initial luminance of 1000 cd m-2 . This superior lifetime could be explained by the C-N bond dissociation energy (BDE) in the host molecular structure. Furthermore, a mixed-host system using the electron-deficient 2,4-bis(dibenzo[b,d]furan-2-yl)-6-phenyl-1,3,5-triazine (DDBFT) is proposed to inhibit the formation of the anion state of our host materials. In short, the device operational lifetime is further improved by applying DDBFT. The carbazole-based asymmetric host molecule containing a pyridine core realizes a high-efficiency blue TADF-OLED showing a positive effect on the operating lifetime, and can provide useful strategies for designing new host materials.

A Simplified Two-Group Multipoint Kinetics Model

Abstract Detailed multiphysics modeling of nuclear power plants has become a necessity in the era of best-estimate analysis. For a number of transients with strong coupling between the neutronics in the reactor core and the fluid-dynamics in the primary circuit and overall heat transfer, it is required to carry out coupled system thermal hydraulics and core three-dimensional (3D) neutronics analysis. Point kinetics approach in the system thermal-hydraulics (TH) code RELAP5 limits its use for many reactivity-induced transients, which involve asymmetric core behavior. In a recent development, a simplified multipoint kinetics model has been coupled with system TH code RELAP5 to circumvent its inadequacy for the analysis of reactivity-induced transients involving asymmetric core behavior. The objective of this paper is to validate the simplified multipoint kinetics model against an asymmetric fast transient benchmark problem in a large power reactor. Time-step and nodalization sensitivity studies have been performed. It is demonstrated that the multipoint kinetics model results are in good agreement with the benchmark, advocating its applicability.

Helical distributed feedback fiber Bragg gratings and rocking filters in a 3D printed preform-drawn fiber.

Using induced UV attenuation across a twisted fiber asymmetric core drawn from a 3D printed preform, linear fiber Bragg gratings (FBGs) are produced on one side of the core. By removing the twist, a helical grating with a period matching the twist rate is produced. Balancing the rate with the polarization beat length in a form birefringent fiber allows the production of a combined rocking filter and FBG device with tunable properties. Direct observation of the fiber grating dispersion within the rocking filter rejection band is possible.

Very Long Baseline Interferometry Observations of the Proposed Radio Counterpart of an EGRET Source

We present high-resolution radio interferometric imaging observations of the radio source NVSS J182659+343113 (hereafter J1826+3431), the proposed radio counterpart of the γ-ray source, 3EG J1824+3441 detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory satellite. We analyzed eight epochs of archival multi-frequency very long baseline interferometry data. We imaged the asymmetric core–jet structure of the source, and detected apparent superluminal motion in the jet. At the highest observing frequency, 15.3 GHz, the core shows high brightness temperature indicating Doppler boosting. Additionally, the radio features undergo substantial flux density variability. These findings strengthen the previous claim of the association of the blazar J1826+3431 with the possible γ-ray source, 3EG J1824+3441.

Plasmonic refractive index sensor based on D-shaped photonic crystal fiber for wider range of refractive index detection

A surface plasmon resonance (SPR) sensor based on D-shaped photonic crystal fiber (PCF) for a wider range of refractive index (RI) detection is proposed in this paper. Two nanoscale gold belts as plasmonic material for SPR are deposited on the D-shaped PCF plane. Asymmetric core enhances birefringence and makes the coupling of the y-polarized mode stronger. Numerical results indicate that wavelength sensitivities of 1700–12,600 nm/RIU can be obtained in the sensing range of 1.15–1.36. The maximum sensor resolution reaches to 7.94 × 10−6 RIU. The proposed sensor is suitable for the detection of low RI analytes, bio-sensing and chemical analysis.