Changes In Molecular Orientation Research Articles

Anisotropic spin transport and photoresponse characteristics detected by tip movement in magnetic single-molecule junction

Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions. Here, using the first-principles method, we theoretically investigate spin transport properties and photoresponse characteristics in trimesic acid magnetic single-molecule junctions with different molecular adsorption orientations and electrode contact sites. The transport calculations indicate that a single-molecule switch and a significant enhancement of spin transport and photoresponse can be achieved when the molecular adsorption orientation changes from planar geometry to upright geometry. The maximum spin polarization of current and photocurrent in upright molecular junctions exceeds 90%. Moreover, as the Ni tip electrode moves, the tunneling magnetoresistance of upright molecular junctions can be increased to 70%. The analysis of the spin-dependent PDOS elucidates that the spinterfaces between organic molecule and ferromagnetic electrodes are modulated by molecular adsorption orientation, where the molecule in upright molecular junctions yields higher spin polarization. Our theoretical work paves the way for designing spintronic devices and optoelectronic devices with anisotropic functionality base on anisotropic molecules.

STUDY OF INTEGRATION, DISTRIBUTION AND DEGRADATION OF SUGARCANE BAGASSE FIBER AS PARTIAL REPLACEMENT FOR FINE AGGREGATE IN CONCRETE SAMPLES

In this study, structural and morphological characterizations were carried out to evaluate the integration, distribution and degradation of sugarcane bagasse fiber (CBF) in a concrete matrix. The samples for evaluation were modified by adding CBF in 0.5% and 1% wt proportions. The modified concrete specimens were exposed to different aggressive conditions over four years before use. The chemical and structural properties of the modified samples were evaluated using Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, while the morphology, distribution and fiber degradation in the samples were determined using scanning electron microscopy and confocal laser scanning microscopy, respectively. The results obtained from spectroscopy and X-ray diffraction indicated the presence of cellulose, and showed a change in molecular orientation, which was attributed to the hydrolysis reaction. The microscopy analyses revealed that the CBF did not undergo degradation.

Effects of chalcogenophene π-bridges on benzodifuran-based polymers for high-performance organic solar cells

The π bridge plays a key role in the photovoltaic performance regulation of donor-π bridge-acceptor (D-π-A) type polymer donors. However, the exploration of suitable π bridges is comparatively understudied compared to the design strategies of the D and A units, especially for benzodifuran (BDF)-based polymers. In this work, we design and synthesize three polymers F10-fu, F10-th, and F10-se with BDF as the donor unit and furan, thiophene, and selenophene as π bridges, respectively. As the π bridge changes from furan to thiophene to selenophene, the corresponding polymers exhibit gradually red-shifted absorption and up-shifted energy levels, and the molecular orientation changes from face-on to a clear coexistence of edge-on and face-on. When blended with a narrow bandgap nonfullerene acceptor (NFA) Y18, the F10-fu, F10-th, and F10-se-based devices display gradually decreased open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF). As a result, the power conversion efficiency (PCE) of the F10-fu:Y18-based device is 16.79%, which is superior to that of the F10-th:Y18 (15.68%) and F10-se:Y18 (14.18%). Similarly, the same pattern is shown when combined with a wide bandgap NFA IT-M. It is believed that the results would offer a new strategy to develop polymer donors for high-performance OSCs.

Molecular-orientation-dependent magnetic properties of iron phthalocyanine (FePc) thin films and microwires

The development of molecular magnets plays a major role in emerging organic spintronics applications, as it exhibits both semiconducting and magnetic properties. Herein, we report on the molecular-orientation-dependent magnetic properties of iron phthalocyanine (FePc) thin films and microwires. FePc thin films grown on SiO2 and flexible kapton substrates clearly reveal that the morphology is strongly influenced by the substrates and film thickness. Meanwhile, the molecular stacking orientation of FePc thin films can be tuned by 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) templating layer and film thickness. Magnetic hysteresis loops show that the iron atoms are strongly magnetically coupled into ferromagnetic chains at low temperature with high coercivity at 1000 Oe. The magnetization and susceptibility of FePc thin films are dependent on the molecular orientation, and the Curie–Weiss constant is modulated from 24 ± 2 K K to 35 ± 2 K through the templating effect, in which the molecular stacking orientation changes from standing-up to lying-down arrangement. Furthermore, strong orientation dependent ferromagnetism is also observed in low-dimensional η-FePc microwires, in which the Curie–Weiss constants change from 20 ± 2 K to 35 ± 2 K when magnetic field rotated from short wire axis to long wire axis. The ability to fabricate FePc thin films on flexible substrate with controllable molecular orientation and ferromagnetism makes them promising candidates for flexible spintronic devices.

Mesoscopic Simulation of Centrifugal Melt Electrospinning of PPESK

AbstractPoly(aryl ether sulfone ketone) (PPESK) is an engineering plastic with high strength, good heat resistance, insulation, and chemical corrosion resistance. The properties of PPESK fiber prepared by centrifugal melt electrospinning can be improved, and the method is efficient and environmentally friendly. This article employs a systematic analysis to investigate the impact of process parameters on the jet formation process, jet motion, fiber diameter, fiber yield, and changes in molecular chain orientation of PPESK. The analysis uses dissipative particle dynamics simulation to reveal that PPESK fibers can attain a certain degree of refinement, and fiber yield can be increased with an appropriate increase in rotational speed, temperature, and electric field force. Moreover, for PPESK with different chain lengths, longer molecular chains impede the untwisting of the molecular chains within the fiber, weakening the fiber orientation, increasing fiber diameter, and resulting in a slower fiber yield increase. These simulation results provide theoretical guidance for preparing PPESK ultrafine fibers with the required performance, shortening the exploration process of actual spinning, and saving time and labor.

Dissolution of viscose rayon multifilament yarn in the ionic liquid 1-ethyl-3-methylimidazolium acetate studied using time–temperature superposition

AbstractWide-angle X-ray diffraction (WAXS) and mechanical testing techniques are used to track the dissolution of a viscose rayon multifilament yarn in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim]+ [OAc]− for different times and temperatures. In the dissolution process, the oriented cellulose II crystals in the regenerated cellulose fibres dissolve and then reform into randomly oriented crystals to form a matrix phase, and this change in orientation enables us to follow the dissolution process using WAXS, and hence determine the dissolved matrix volume fraction $${v}_{m}$$ v m . The change in the average molecular orientation $${P}_{2}$$ P 2 determined from an azimuthal $$(\alpha$$ ( α ) X-ray scan, allows the growth of the matrix volume fraction $${v}_{m}$$ v m to be calculated with time and temperature. The growth of $${v}_{m}$$ v m was found to follow time temperature superposition, with an Arrhenius behaviour, giving a value for the activation energy of Ea = 149 ± 4 kJ/mol. Young’s modulus was measured on all the resulting processed composites. The fall of Young’s modulus with dissolution time and temperature was also found to follow time–temperature superposition, with an Arrhenius behaviour giving a value for Ea = 198 ± 29 kJ/mol. The Young’s Modulus results plotted against $${v}_{m}$$ v m determined from the WAXS measurements fitted well to the Voigt upper bound parallel Rule of Mixtures $$.$$ .

Self-Assembled Microactuators Using Chiral Liquid Crystal Elastomers.

Materials that undergo reversible changes in form typically require top-down processing to program the microstructure of the material. As a result, it is difficult to program microscale, 3D shape-morphing materials that undergo non-uniaxial deformations. Here, a simple bottom-up fabrication approach to prepare bending microactuators is described. Spontaneous self-assembly of liquid crystal (LC) monomers with controlled chirality within 3D micromold results in a change in molecular orientation across thickness of the microstructure. As a result, heating induces bending in these microactuators. The concentration of chiral dopant is varied to adjust the chirality of the monomer mixture. Liquid crystal elastomer (LCE) microactuators doped with 0.05 wt% of chiral dopant produce needle-shaped actuators that bend from flat to an angle of 27.2 ± 11.3° at 180 °C. Higher concentrations of chiral dopant lead to actuators with reduced bending, and lower concentrations of chiral dopant lead to actuators with poorly controlled bending. Asymmetric molecular alignment inside 3D structure is confirmed by sectioning actuators. Arrays of microactuators that all bend in the same direction can be fabricated if symmetry of geometry of the microstructure is broken. It is envisioned that the new platform to synthesize microstructures can further be applied in soft robotics and biomedical devices.

Deflecting and routing nematicons via orientation programmable liquid crystal array.

By designing a liquid crystal cell with comb electrode structure, the alignment modulation of nematic liquid crystal in the cell can be realized after the electric field is applied. In different orientation regions, the incident laser beam can deflect at different angles. At the same time, by changing the incident angle of the laser beam, the reflection modulation of the laser beam on the interface of the liquid crystal molecular orientation change can be realized. Based on the above discussion, we then demonstrate the modulation of liquid crystal molecular orientation arrays on nematicon pairs. In different orientation regions of liquid crystal molecules, nematicon pairs can exhibit various combinations of deflections, and these deflection angles are modulable under external fields. Deflection and modulation of nematicon pairs have potential applications in optical routing and optical communication.

Optical and flexoelectric biosensing based on a hybrid-aligned liquid crystal of anomalously small bend elastic constant

Liquid crystal (LC)-based biosensors rely on the response of the LC molecules to perturbation generated by analytes at the interface, leading to the susceptible change in molecular alignment or orientation. The sensitivity of these biosensors is primarily dependent on the LC's material properties and surface anchoring strength. By incorporation of an unconventional mesogenic compound (CB7CB) coupled with the hybrid-alignment cell configuration, this work presents a binary nematic LC for label-free biosensing, manifesting a novel sensing technology that takes advantage of CB7CB-induced flexoelectricity in the transducer. Herein, we prepared LC mixtures by blending a typical rod-like nematic LC (E7) with the bent-core mesogen CB7CB in various weight ratios and studied the effect of the CB7CB content on E7/CB7CB-based biosensing performance in vertically aligned and hybrid-aligned nematic (HAN) cells. Owing to the anomalously small bend elastic constant K33 in CB7CB, the mixture designated CB45 with the highest CB7CB weight percentage (45 wt% in this study) was best applicable to biosensing in HAN cells. When observed under a polarizing optical microscope, CB45 in the HAN geometry showed the capability of detection of as low as 10−10 g/mL for the protein standard bovine serum albumin (BSA). Moreover, the quantitation of the assay was fulfilled by both dielectric and light transmission measurements of the hybrid-aligned cholesteric CB45/R5011. The limit of detection of 7 × 10−10 g/mL was achieved by spectrometric analysis. To the best of our knowledge, this work is the first to demonstrate flexoelectric biosensing on the basis of flexoelectric polarization associated with giant flexoelectricity in CB7CB partially constituting the LC transducer.

F4-TCNQ on Epitaxial Bi-Layer Graphene: Concentration- and Orientation-Dependent Charge Transfer at the Interface

Bi-layer epitaxial graphene (BLG) on 6H-SiC(0001) (EG/SiC) was grown and modified by thermal deposition of the molecular electron acceptor tetrafluoro-tetra cyano quinodimethane (F4-TCNQ). The surface-modified system, F4-TCNQ/EG/SiC, was studied by X-ray photoelectron spectroscopy (XPS) and angle-resolved polarized Raman spectroscopy (ARPRS). XPS results indicate that bonding of deposited F4-TCNQ molecules depends on their concentration. Although bonding through the cyano groups is present at all concentrations, charge transfer from graphene to fluorine is evident only at sub-monolayer concentrations. The corresponding change in bond character is coupled with a change in molecular orientation. Raman spectroscopy not only provides results consistent with the findings from the XPS study but also reveals a significant degree of molecular stacking above the monolayer concentration. Thus, both the variation of the acceptor concentration and the number of graphene layers provide further handles to manipulate charge and doping that may be useful in device applications.

PH-Induced Changes in the SERS Spectrum of Thiophenol at Gold Electrodes during Cyclic Voltammetry.

Thiophenol is a model compound used in the study of self-assembly of arylthiols on gold surfaces. In particular, changes in the surface-enhanced Raman scattering (SERS) spectra of these self-assembled monolayers (SAMs) with a change of conditions have been ascribed to, for example, differences in orientation with respect to the surface, protonation state, and electrode potential. Here, we show that potential-induced changes in the SERS spectra of SAMs of thiophenol on electrochemically roughened gold surfaces can be due to local pH changes at the electrode. The changes observed during the potential step and cyclic voltammetry experiments are identical to those induced by acid–base switching experiments in a protic solvent. The data indicate that the potential-dependent spectral changes, assigned earlier to changes in molecular orientation with respect to the surface, can be ascribed to changes in the pH locally at the electrode. The pH at the electrode can change as much as several pH units during electrochemical measurements that reach positive potentials where oxidation of adventitious water can occur. Furthermore, once perturbed by applying positive potentials, the pH at the electrode takes considerable time to recover to that of the bulk solution. It is noted that the changes in pH even during cyclic voltammetry in organic solvents can be equivalent to the addition of strong acids, such as CF3SO3H, and such effects should be considered in the study of the redox chemistry of pH-sensitive redox systems and potential-dependent SERS in particular.

Molecular dynamics simulation of yield thixotropy of crude oil systems

In the work, molecular dynamics simulation is employed to analyze the micro mechanism of the yield thixotropy of crude oil. The effects of different shear rates on the yield thixotropic characteristics of the crude oil systems are investigated based on the Shengli crude oil system and the Nanyang crude oil system. The yield thixotropic mechanism of the crude oil systems is revealed by analyzing the orientation of the crude oil molecules, the extension degree in the molecular chain of crude oil, and the energy of the system. The results show that at the beginning of shearing, the molecular chain of crude oil gradually curls to prevent the changes in molecular orientation, and then a small amount of distortion occurs and the shear stress gradually increases. In the process of shear failure, the number of trans configuration molecules gradually increases and the number of Ponzi configuration and homeopathic configuration molecules decreases. The molecular chain of the crude oil gradually extends and the crude oil molecules show a directional arrangement consistent with shear direction, and the shear stress decreases.

Electronic Distribution of SN2 IRC and TS Structures: Infrared Intensities of Imaginary Frequencies.

A novel IRC-TS-CCTDP method to investigate transition states (TS) is proposed in which changes in the molecular geometry follow atomic displacements corresponding to the imaginary frequency normal coordinate. Electronic charge structure changes can be analyzed using the charge-charge-transfer-dipolar polarization (CCTDP) model. An application is presented for the gas-phase SN2 reaction transition state structures for nine NuCX3LG- systems, with Nu and LG = H, F, Cl and X = H, F. Using quantum theory of atoms in molecules (QTAIM) at the QCISD/aug-cc-pVTZ level, atomic charges and atomic dipoles were obtained and applied to calculate the CCTDP contributions to their imaginary normal mode intensities. The results show that the imaginary bands are exceptionally strong, ranging from 1217 to 16 086 km·mol-1, much higher than the stretching intensities found in the methyl halides (that are all less than 100 km·mol-1). For all systems, the CT contributions are responsible for 63% of the total dipole moment derivatives. The charge contributions are slightly higher for transition states where X = F. Dipolar polarization contributions are always small and only reflect the molecular orientation change when the nucleophile displaces the leaving group and, therefore, can be neglected. The same occurs for contributions from the X atoms. Only atoms aligned with the reaction axis Nu--C-LG contribute to the total intensity. Almost all of the infrared intensities are determined by electron transfers from the nucleophile to carbon and subsequently from carbon to the leaving group. The mechanism of charge transfer revealed by the CCTDP model is consistent with the well-accepted reaction mechanism. Open-access codes for performing the IRC-TS-CCTDP analysis are described and provided for potential users in the Supporting Information.

Flow Marks in Injection Molding of PP

Abstract Flow marks in injection moulding is quite often encountered on different type of polymers. This defects is known as successive and periodic bright and dull bands oriented perpendicular to the flow direction. Their appearances meanly depend on processing and observation conditions. This study was lead on two industrial polypropylene polymers with a simplified polished rectangular mould geometry. We show that this defect appears during the filling stage and comes from a local change of morphological and molecular orientation along the filling direction on the surface. An instability of the flow front due to a limited sliding at the contact combined to the strong changed of molecular orientation before and after the stagnation point are invoked to explain this instability.

Atomic-scale insights into the colossal barocaloric effects of neopentyl glycol plastic crystals

Neopentyl glycol has become an important candidate material for solid-state refrigeration in the future because of its environmental protection, high energy efficiency, high stability, and economy. However, the complete micro-dynamic mechanism remains to be established, which restricts its further applications. In this work, we investigate one representative material-plastic crystal neopentyl glycol (NPG) by means of large-scale molecular dynamics simulation. It is found that NPG exhibits colossal barocaloric effects (CBCEs) with high isothermal entropy changes and potentially large adiabatic temperature changes, which closely relates to the reversible order disorder change in NPG's molecular orientation, in which the non-bond interaction between molecules plays a key role. Further analysis of orientational dynamics and hydrogen bond energy during phase transition along with pressure dependent thermal conductivity sheds light on the underlying microscopic mechanism. Our work reveals the molecular mechanism of CBCEs in NPG as a prototypical plastic crystal, providing valuable insight into achieving practical caloric materials in future cooling technology.

Relationship between Molecular Orientation Relaxation during Physical Aging and Heat Resistance of Polystyrene Injection Moldings

Abstract This work examined the relationship between changes in molecular orientation and the heat resistance (heat distortion temperature) of polystyrene injection moldings following heat treatment below the glass transition temperature. Molecular orientation around the core layer of the injection moldings was found to be relaxed by the heat treatment. Also, in the untreated specimen, the molecular orientation around the core layer was relaxed from 60°C during the heating process. Since loss tangent (tanδ) also increased from 60°C during the heating process in the untreated specimen, it was considered that the increase in tanδ occurred with the molecular motion due to the relaxation of molecular orientation from 60°C. After the heat treatment, because of the relaxation of molecular orientation around the core layer by the heat treatment, the relaxation of molecular orientation from 60 °C did not occur during the subsequent heating process, and the tanδ of the polymer between 60 and 90 °C was decreased. Because this decrease in the tanδ over this temperature range improved the heat resistance of the material, the enhanced heat resistance by the heat treatment was attributed to the suppression of the relaxation of molecular orientation from 60°C during the heating process. Furthermore, relaxation of molecular orientation and enthalpy relaxation were related to improvement in the heat resistance.

Mechano‐Optical Sensors Fabricated with Multilayered Liquid Crystal Elastomers Exhibiting Tunable Deformation Recovery

AbstractAdvances in tuning the mechanoresponsive behavior of liquid crystal elastomers have facilitated the development of next‐generation applications such as reconfigurable photonic/electronic materials, energy‐harvesting devices, and flexible sensors. However, the molecular‐level control of mechanical responses remains difficult, with limited tunability achieved for recovery processes after stimulus removal. Herein, a design concept is proposed for facilely tuning the recovery of both the macroscopic deformation and molecular orientation change of liquid crystal elastomers using layered materials that exhibit the desired mechanoresponsive behavior. Changing the layering materials (a polydimethylsiloxane film with elastic response to a polymethylpenten film with plastic response) alters the relaxation time from <1 s to >6 months. To demonstrate this concept, highly sensitive, stretchable mechano‐optical sensors with fast and ultraslow recovery times are developed that enable an applied strain to be quantitatively detected in real time or memorized with high spatial resolution, even with a conventional camera. This material design concept for arbitrarily controlling the recovery response can provide a platform for stimuli‐responsive applications.

Analysis of Molecular Interactions between Components in Phospholipid-Immunosuppressant-Antioxidant Mixed Langmuir Films.

The study of Langmuir monolayers incorporating biomimetic and bioactive substances plays an important role today in assessing the properties and quality of the molecular films for potential biomedical applications. Here, miscibility of binary and ternary monolayers of phospholipid (dioleoyl phosphatidylcholine, DOPC), immunosuppressant (cyclosporine A, CsA), and antioxidant (lauryl gallate, LG) of varying molar fractions was analyzed by means of the Langmuir technique coupled with a surface potential (ΔV) module at the air–water interface. The surface pressure–area per molecule (π–A) isotherms provided information on the physical state of the films at a given surface pressure, the monolayer packing and ordering, and the type and strength of intermolecular interactions. Surface potential–area (ΔV–A) isotherms revealed the molecular orientation changes at the interface upon compression. In addition, the apparent dipole moment of the monolayer-forming molecules was determined from the surface potential isotherms. The obtained results indicated that the film compression provoked subsequent changes of CsA conformation and/or orientation, conferring better affinity for the hydrocarbon environment. The mutual interactions between the components were analyzed here in terms of the excess and total Gibbs energy of mixing, whose values depended on the stoichiometry of the mixed films. The strongest attraction, thus the highest thermodynamic stability, was found for a DOPC–CsA–LG mixture with a 1:1:2 molar ratio. Based on these results, a molecular model for the organization of the molecules within the Langmuir film was proposed. Through this model, we elucidated the significant role of LG in improving the miscibility of CsA in the model DOPC membrane and thus in increasing the stability of self-assembled monolayers by noncovalent interactions, such as H-bonds and Lifshitz–van der Waals forces. The above 1:1:2 combination of three components is revealed as the most promising film composition for the modification of implant device surfaces to improve their biocompatibility. Further insight into mechanisms concerning drug–membrane interactions at the molecular level is provided, which results in great importance for biocoating design and development as well as for drug release at target sites.

Investigation on the origin of friction and superlubricity

Friction consumes about a third of the world’s primary energy, wear causes about 80% of machine parts to fail, and the economic losses caused by friction and wear account for about 2%–7% of its gross domestic product (GDP) for different countries every year. For large manufacturing countries such as China, the loss caused by friction and wear is relatively high. If we only calculate by 5%, the loss caused by friction and wear in China in 2019 may reach 4.95 trillion RMB. Therefore, how to reduce friction and wear is a widely concerned problem, and it is also one of the key factors that affect the human society to go green, environmental protection, and effective use of resources and energy. In present paper, advancements in the research of the origin of friction and in superlubricity have been reviewed, in which most is from my group. In the part of the origin of friction, the energy dissipation mechanism of micro-friction has been introduced firstly. The works on such area by molecular dynamics simulation showed that the friction generation process will be accompanied by the energy dissipation of phonons, electrons and acoustic-electric coupling modes. The dissipative form of sliding kinetic energy is mainly that the sliding process produces lattice vibration, which makes the energy irreversibly dissipated in the form of phonons. However, the phonon dissipation measurements of the tribo-process have not been reported at present and all these results need to be proved. Our group developed a friction energy dissipation measurement system, which can realize the measurement of various emission of friction process, phonon and electron dissipation process, molecular orientation change, micro friction force and ultra-low friction coefficient. By such system, it is found that the defects will trap neutral excitons and cause the excitons to dissipate energy faster, and also can reduce the exciton diffusion length significantly. Superlubricity is a new technique that reduces the friction coefficient by several orders of magnitude, accompanied by orders of magnitude decrease in wear rate. It is divided into three sides, one is solid superlubricity, and another is liquid superlubricity, and then is the combine superlubricity of liquids and solids. In the part of solid superlubricity, the introduction of the concept of superlubricity and the latest research progress on the superlubricity properties of 2D materials, such as molybdenum disulfide, boron nitride, graphite, and graphene, are introduced. The lowest friction coefficient for 2D materials about 0.00002 has been gotten in my group. In the amorphous carbon system we achieve superlubricity state with friction coefficient about 0.0001 under low temperature (−110°C) and high pressure (>2 GPa). In the field of liquid superlubricity, it has developed very rapidly in the past 20 years. We conclude three mechanisms for liquid superlubricity: Fluid hydrodynamic effects, double layer force and hydration force. Sometimes one mechanism can lead to superlubricity, and sometimes it requires the joint action of two or three mechanisms. Supported by these three mechanisms, the liquid superlubricity bearing capacity has been improved from about 10 MPa 20 years ago to more than 300 MPa; the system composed of water agent has been extended to solutions (acid, alkali, salt), alcohol-based liquids, oil-based system etc.; and the materials of friction pair are extended from mica, ceramics to sapphire, metal, DLC (diamond-like carbon) film, etc. In addition, recently 2D materials as additives have been added to liquid to form a liquid-solid combined superlubricity state in my group and the bearing pressure has greatly increased to the GPa level, which is a big step forward for the application of liquid superlubricity. Therefore, the time has come for the engineering application of superlubricity, and the concept of “superlubricitive engineering” has been proposed.

Significantly Increasing the Power Conversion Efficiency by Controlling the Orientation of Nonfullerene Small Molecular Acceptors via Side Chain Engineering

Three S,N‐heteroacene nonfullenere small molecular acceptors (NF‐SMAs) with different branching positions on side chains named SNBDT1‐F, SNBDT2‐F, and SNBDT3‐F are synthesized to understand the relationship among branching positions, molecular orientations of NF‐SMAs, and photovoltaic performance of nonfullerene organic solar cells (OSCs). When the branching position is moved close to the conjugated backbone, the proportion of face‐on orientation increases gradually from 4% (SNBDT3‐F), 16% (SNBDT2‐F), to 44% (SNBDT1‐F), suggesting that the molecular orientation changes from edge‐on to face‐on, which has a positive influence on exciton dissociation and charge transport. As a result, the device based on PBDB‐T:SNBDT1‐F shows the highest exciton dissociation probability and carrier mobilities due to the highest proportion of face‐on orientation of SNBDT1‐F. Therefore, the highest power conversion efficiency (PCE) of 12.70% with a high short‐circuit current (Jsc) of 20.97 mA cm−2 and a fill factor of 70.4% is obtained for SNBDT1‐F‐based device, which is much higher than PCEs of SNBDT2‐F‐based (6.57%) and SNBDT3‐F‐based devices (5.87%). Overall, these results provide deep insight into the relationship among the branching positions, molecular orientation, and photovoltaic performance in nonfullerene OSCs, which is important for designing new NF‐SMAs with face‐on orientation and promoting the development of nonfullerene OSCs.