Asymmetric Building Blocks Research Articles

Spin Filtering and Amplification in Self-Assembled Nanofibers Based on Chiral Asymmetric Building Blocks.

The cooperativity in artificial self-assembling systems can be enhanced to expand their applications and redesign their properties. Recently, chiral molecules have garnered renewed attention due to their potential as highly efficient spin filters through the chiral-induced spin selectivity (CISS) effect. However, the potential of asymmetric building blocks based on chiral perylene diimides (PDIs) self-assembled materials to generate a spin-polarized current is still not widely acknowledged. In this work, we have demonstrated that nanofibers derived from "asymmetric PDIs" molecules have been found to exhibit promising spin-filtering property and the amplification of spin polarization at room temperature. Also, the exploration of chiral amplification and correlating it with the amplification of spin polarization have been reported for the first time through this work. These findings underscore the significance of self-assembled materials in the realm of spintronics, as they offer fascinating platforms with evolving structure-property relationship. It also provides the feasible possibility of enhancing the CISS-based spintronic devices that can accomplish controllability and high spin-filtering efficiency simultaneously.

Chiral Spectroscopy of Nanostructures.

ConspectusChirality is ubiquitous in the universe and in living creatures over detectable length scales from the subatomic to the galactic, as exemplified in the two extremes by subatomic particles (neutrinos) and spiral galaxies. Between them are living creatures that display multiple levels of chirality emerging from hierarchically assembled asymmetric building blocks. Not too far from the bottom of this pyramid are the foundational building blocks with chiral atomic centers on sp3 carbon atoms exemplified by l-amino acids and d-sugars that are self-assembled into higher-order structures with increasing dimensions forming highly complex, amazingly functional, and energy-efficient living systems. The organization and materials employed in their construction inspired scientists to replicate complex living systems via the self-assembly of chiral components. Multiple studies pointed to unexpected and unique electromagnetic properties of chiral structures with nanoscale and microscale dimensions, including giant circular dichroism and collective circularly polarized scattering that their constituent units did not possess.To address the wide variety of chiral geometries observed in continuous materials, singular particles, and their complex systems, multiple analytic techniques are needed. Simultaneously, their spectroscopic properties create a pathway to multiple applications. For example, mirror-asymmetric vibrations at chiral centers formed by sp3 carbon atoms lead to optical activity for the infrared (IR) wavelength regions. At the same time, understanding the optical activity in, for example, the IR region enables biomedical applications because multiple modalities of biomedical imaging and vibrational optical activity (VOA) of biomolecules are known for IR range. In turn, VOA can be realized in both absorption and emission modalities due to large magnetic transition moments, as vibrational circular dichroism (VCD) or Raman optical activity (ROA) spectroscopy. In addition to the VOA, in the range of longer wavelengths, lattice vibrational mode or phononic behavior occurs in chiral crystals and nanoassemblies, which can be readily detected by terahertz circular dichroism (TCD) spectroscopy. Meanwhile, chiral self-assembly can induce circularly polarized light emission (CPLE) regardless of the existence of chirality in coassembled fluorophores. The CPLE from self-assembled chiral materials is particularly interesting because the CPLE can originate from both circularly polarized luminescence and circularly polarized scattering (CPS). Furthermore, because self-assembled nanostructures often exhibit stronger optical activity than their building blocks owing to dimension and resonance effects, the optical activity of single assembled nanostructures can be investigated by using microscopic technology combined with chiral optics. Here, we describe the state of the art for spectroscopic methods for the comprehensive analysis of chiral nanomaterials at various photon wavelengths, addressed with special attention given to new tools emerging both for materials with self-organized hierarchical chirality and single-particle spectroscopy.

Benzimidazole-based covalent organic framework embedding single-atom Pt sites for visible-light-driven photocatalytic hydrogen evolution

Visible-light-driven photocatalytic hydrogen evolution reaction (HER) over a semiconductor provides an effective avenue to produce renewable clean energy and alleviate energy and environmental crises. However, the HER efficiency is still limited by the sluggish electron transfer process. Herein, a highly active covalent organic framework (COF) was constructed from the unusual benzimidazole monomer in a microwave-assisted solvothermal pathway. With single-atom Pt sites as cocatalyst, the catalyst exhibited an HER rate up to 115 mmol g–1 h–1 and a high turnover frequency of 4475.1 h–1 under visible-light irradiation. The above performance relied on the combination of benzimidazole moieties and COF framework, which, on the one hand, stabilized photogenerated electrons to prolong the electron lifetime, and on the other hand provided a strong host-guest interaction that resulted in the creation of single-atom Pt sites and the acceleration of the electron-transfer to the active sites for proton reduction. This work demonstrates the perspective of electron stabilization and interfacial charge transfer avenue construction in the HER process, which can be reached by a molecular-level design of COF-based organic semiconductors by using structural and functional diverse asymmetric building blocks.

Rational Design of a Rare-Earth Oxychalcogenide Nd3 [Ga3 O3 S3 ][Ge2 O7 ] with Superior Infrared Nonlinear Optical Performance.

Inorganic chalcogenides have been studied as the most promising infrared (IR) nonlinear optical (NLO) candidates for the past decades. However, it is proven difficult to discover high-performance materials that combine the often-incompatible properties of large energy gap (Eg ) and strong second harmonic generation (SHG) response (deff ), especially for rare-earth chalcogenides. Herein, centrosymmetric Cs3 [Sb3 O6 ][Ge2 O7 ] is selected as a maternal structure and a new noncentrosymmetric rare-earth oxychalcogenide, namely, Nd3 [Ga3 O3 S3 ][Ge2 O7 ], is successfully designed and obtained by the module substitution strategy for the first time. Especially, Nd3 [Ga3 O3 S3 ][Ge2 O7 ] is the first case of breaking the trade-off relationship between wide Eg (>3.5eV) and large deff (>0.5 × AgGaS2 ) in rare-earth chalcogenide system, and thus displays an outstanding IR-NLO comprehensive performance. Detailed structure analyses and theoretical studies reveal that the NLO effect originates mainly from the cooperation of heteroanionic [GaO2 S2 ] and [NdO2 S6 ] asymmetric building blocks. This work not only presents an excellent rare-earth IR-NLO candidate, but also plays a crucial role in the rational structure design of other NLO materials in which both large Eg and strong deff are pursued.

Heterocyclic Synthesis of Crowded Aposafranones: Structure of 1-Methyl-8-dimethylamino-10-phenylphenazin-2-(10H)one and Related Compounds.

Oxidative condensation of three p-phenylenediamines with 3-hydroxy-2-methyl-N-(phenylamino)benzene gives new coloured aposafranones. 2-Methylresorcinol is easy to convert into the asymmetric building block 3-hydroxy-2-methyl-N-(phenylamino)benzene with aniline. The aposafranones are sterically crowded because of the 1-methyl and N-phenyl groups. The UV/Vis absorption maxima are in the range 530-545 nm.

Toward High-Performance Electrochromic Conjugated Polymers: Influence of Local Chemical Environment and Side-Chain Engineering

Three homologous electrochromic conjugated polymers, each containing an asymmetric building block but decorated with distinct alkyl chains, were designed and synthesized using electrochemical polymerization in this study. The corresponding monomers, namely T610FBTT810, DT6FBT, and DT48FBT, comprise the same backbone structure, i.e., an asymmetric 5-fluorobenzo[c][1,2,5]thiadiazole unit substituted by two thiophene terminals, but were decorated with different types of alkyl chain (hexyl, 2-butyloctyl, 2-hexyldecyl, or 2-octyldecyl). The effects of the side-chain structure and asymmetric repeating unit on the optical absorption, electrochemistry, morphology, and electrochromic properties were investigated comparatively. It was found that the electrochromism conjugated polymer, originating from DT6FBT with the shortest and linear alkyl chain, exhibits the best electrochromic performance with a 25% optical contrast ratio and a 0.3 s response time. The flexible electrochromic device of PDT6FBT achieved reversible colors of navy and cyan between the neutral and oxidized states, consistent with the non-device phenomenon. These results demonstrate that subtle modification of the side chain is able to change the electrochromic properties of conjugated polymers.

Tuning the Mechanical and Electric Properties of Conjugated Polymer Semiconductors: Side‐Chain Design Based on Asymmetric Benzodithiophene Building Blocks

AbstractUnderstanding molecular design rules for stretchable polymer semiconductors is important for enabling next generation stretchable electronic circuits. To simultaneously improve both electrical properties and mechanical stretchability, a design strategy is reported in introducing conjugated rigid fused‐rings with bulky side groups in semiconducting polymers. In this work, the understanding of this design concept is improved by systematically investigating the effect of different types of bulky side groups asymmetrically substituted on conjugated polymer semiconductor backbones. Specifically, four types of side groups are investigated, including naphthalene (NaPh), biphenyl (PhPh), thienylphenyl (ThPh), and alkylphenyl (C4Ph), asymmetrically substituted on benzodithiophene units, namely asy‐BDT. With the four types of side groups installed on BDT‐containing conjugated polymers in an asymmetrical fashion, it is observed that they reduced the polymer chain aggregation and film crystallinity, hence improving the film stretchability. Furthermore, the fully conjugated polymer backbone allows maintenance of good charge carrier mobilities. Specifically, polymer PDPP‐C4Ph (with C4Ph side groups) shows the highest mobility in the fully stretchable transistor and maintained its mobility even after being subjected to hundreds of stretching‐releasing cycles at 25% strain. Overall, the results provide anunderstanding of the use of asymmetrically substituted fused‐ring conjugated polymer structures to tune mechanical and charge transport properties.

Triangular Topological 2D Covalent Organic Frameworks Constructed via Symmetric or Asymmetric "Two-in-One" Type Monomers.

Most of the reported covalent organic frameworks (COFs) so far are prepared from highly symmetric building blocks, which to some extent limits the expansion of COF diversity and complexity. Low‐symmetric building blocks can be designed through a desymmetrized vertex strategy, which might be used to construct new topological COFs. But reports of COFs constructed by asymmetric building blocks are thus far very rare. Here, a feasible strategy to design asymmetric building blocks for COF synthesis is introduced, by simply varying the positions of functional groups in the monomer. As a proof of concept, two isomeric hexaphenylbenzene‐based “two‐in‐one” type monomers (1,2,4‐HPB‐NH2 and 1,3,5‐HPB‐NH2) are designed and synthesized. To the authors’ surprise, self‐polycondensation of the asymmetric 1,2,4‐HPB‐NH2 (i.e., the isomer of common C3 ‐symmetric 1,3,5‐HPB‐NH2) also affords highly crystalline COF (1,2,4‐HPB‐COF) similar to the symmetric 1,3,5‐HPB‐NH2 counterpart with identical topological structure. The triangular porous structures of both HPB‐based COFs are well resolved by powder X‐ray diffraction (PXRD), theoretical simulations, nitrogen sorption, and morphologies analysis. This work demonstrates the “two‐in‐one” type asymmetric building blocks can also produce highly crystalline frameworks and thus provides a new structural design strategy for reticular chemistry.

VOC enhancement of thienobenzofuran and benzotriazole backboned photovoltaic polymer by side chain sulfuration or fluoridation

In this work, four wide-bandgap (WBG) conjugated polymers based on asymmetrical building block thieno [2,3f]benzofuran (TBF) and fluorobenzotriazole (BZ), are synthesized and applied as donor materials in polymer solar cells (PSCs). The effect of conjugated side chains (alkylthiothiophenyl, alkylthiophenyl, alkylphenyl and fluoroalkoxyphenyl) on the optical absorption, electrochemical and photovoltaic properties are investigated in detail. These polymers exhibit similar properties, strong absorption from 300 to 650 nm with wide bandgaps ranging from 1.87 to 1.96 eV, excellent thermal stability, the high and balanced carrier mobility. Notably, the open-circuit voltages (VOC) of PTSDO-BZ increases by 0.16 V compared with PTDO-BZ. Similarly, larger VOC changes have also occurred in PPEH-BZ and PPFOEH-BZ comparation. The enhanced VOC can be ascribed to the low-lying highest occupied molecular orbital (HOMO) energy level by incorporating sulfur and fluorine substituents on the conjugated side chains. The as-cast devices of PTSDO-BZ:ITIC exhibit the highest power conversion efficiency (PCE) of 8.66%, with a VOC of 0.88 V, a short-circuit current density (JSC) of 15.06 mA cm−2, and a fill factor (FF) of 65.12%. The results indicate that the modification of the side chains of the TBF unit can effectively lower the HOMO energy levels and thereby obtaining high VOC.

Covalent organic framework mesocrystals through dynamic modulator manipulated mesoscale self-assembly of imine macrocycle precursors

Framework crystallization is an unresolved challenge in the chemistry of covalent organic frameworks (COFs) due to the poorly controlled simultaneous polymerization and crystallization processes. Here, we report the first morphogenesis of COF mesocrystals with two-dimensional hexagonal p6m symmetry through the combination of alkyl amine as a dynamic modulator and 2,4,6- triformylresorcinol imine as an asymmetrical building block. The amine modulator depresses the lateral growth of 2D sheets, and the slow kinetics combined with the asymmetrical conformation of 2,4,6-triformylresorcinol imine lead to the formation of transient imine macrocycles, which further undergo mesoscale self-assembly into nanotubular structures. The nanotubular structures tend to join together into rod-like bundles with ordered hexagonal rods, which finally grow into uniform hexagonal COF mesocrystals. The present strategy opens a nonclassical nucleation and crystal growth approach to create COFs with unexplored mesocrystal structures, which further extends the scope of crystalline framework materials and provides a new strategy for crystal morphogenesis.

Heteroatom substitution-induced asymmetric A–D–A type non-fullerene acceptor for efficient organic solar cells

Abstract Research on asymmetric A–D–A structured non-fullerene acceptors has lagged far behind the development of symmetric counterpart. In this contribution, by simply replacing one sulfur atom in indacenodithiophene unit with a selenium atom, an asymmetric building block SePT and a corresponding asymmetric non-fullerene acceptor SePT-IN have been developed. Asymmetric SePT-IN achieved a high efficiency of 10.20% in organic solar cells when blended with PBT1-C, much higher than that of symmetric TPT-IN counterpart (8.91%). Our results demonstrated an effective heteroatom substitution strategy to develop asymmetric A–D–A structured non-fullerene acceptors.

Simultaneous Control of Interlayer Exchange Coupling and the Interfacial Dzyaloshinskii–Moriya Interaction in Ru-Based Synthetic Antiferromagnets

We present a Ru-based synthetic antiferromagnet (SAF) made with asymmetric ferromagnetic building blocks (Pt/Co/Ir or Ir/Co/Pt) to couple their interfacial Dzyaloshinskii-Moriya interaction (DMI) with strong interlayer exchange coupling (IEC). This combination may lead to new types of antiferromagnetic domain walls (DWs), which are conceptually presented in this letter. These include an energetically frustrated configuration and an “isolated” spin chain where a net magnetization exists only at the DW. While most SAF designs incorporate a Co/Ru/Co IEC layer, chiral SAFs require Pt and/or Ir at the Ru/Co interface. In all cases except Pt/Ru/Pt, a significant IEC field is preserved over a range of Ru thicknesses, with the largest occurring for Ir/Ru/Ir. These results demonstrate that ferromagnetic film stacks with purportedly strong DMI can be incorporated into SAFs without compromising IEC.

High‐Performance Eight‐Membered Indacenodithiophene‐Based Asymmetric A‐D‐A Type Non‐Fullerene Acceptors

Indacenodithiophene (IDT) has been widely used as the central core to design high‐performance acceptor‐donor‐acceptor (A‐D‐A)‐type non‐fullerene acceptors (NFAs). NFAs based on five‐, six‐, seven‐, and nine‐membered IDT have been successfully prepared. However, less research attention has been paid to the eight‐membered IDT derivative. In this study, a novel asymmetric TTPTTT building block as an eight‐membered IDT unit are designed and synthesized. The effect of nonfluorinated, monofluorinated, and difluorinated end‐capping groups on the photovoltaic performance of TTPTTT‐based NFAs are specifically investigated. By blending with the polymer donor PBT1‐C, organic solar cells (OSCs) based on TTPTTT‐IC, TTPTTT‐2F, and TTPTTT‐4F exhibited power conversion efficiencies (PCEs) of 7.91, 11.52, and 12.05%, respectively. Our results indicate that the asymmetric TTPTTT building block as an eight‐membered IDT derivative is a promising central core unit for designing high‐performance A‐D‐A type NFAs.

Programmed Hierarchical Hybrid Nanostructures from Fullerene-Dendrons and Pyrene-Dendrons.

The construction of fullerene (C60 ) hierarchical nanostructures with the help of amphiphilic molecules remains a challenging task in nanoscience and nanotechnology. Utilizing the host-guest complex concept, sub-10 nm layered superstructures are constructed from a monofunctionalized C60 dendron (C60 D, guest) and tweezer-like pyrene dendron (PD, host). Since C60 D and PD are asymmetric shape amphiphiles having liquid crystal (LC) dendrons, both C60 D and PD construct head-to-head bilayer superstructures by themselves. From fluorescence titration experiments, it is realized that the host-guest complex shows 1:1 stoichiometric binding with a binding constant (Ksv = 2.45 × 105 m-1 ). Based on the morphological observations and scattering analyses, it is found that buckle-like asymmetric building blocks (C60 D·PD) are self-assembled by the host-guest complex and construct multilayer hybrid nanostructures. The hierarchical hybrid nanostructures consist of the self-assembled C60 D·PD bilayer with a 2D C60 ·P nanoarray sandwiched between LC dendrons. This advanced strategy is expected to be a practicable and rational guideline for the fabrication of programmed hierarchical hybrid nanostructures.

A small molecular electron acceptor based on asymmetric hexacyclic core of thieno[1,2-b]indaceno[5,6-b′]thienothiophene for efficient fullerene-free polymer solar cells

A novel A-D-A (acceptor-donor-acceptor) type non-fullerene small molecule, A201, consisting of an asymmetric thieno[1,2-b]indaceno[5,6-b′]thienothiophene (TITT) unit as middle D part and 2-(3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (IC) groups as end-capped A parts was designed and synthesized. The asymmetric TITT building block showed a higher dipole moment of 0.85 Debye (1 Debye = 3.33564 × 10−30 cm) compared with the symmetric analogues of indacenodithiophene (IDT) and indacenodithieno[3,2-b]thiophene (IDTT) of 0.098 and 0.13 Debye, respectively. The solution-processed bulk heterojunction solar cells using a benzotriazole (BTA)-based polymer of J71 as donor and A201 as acceptor, showed a power conversion efficiency (PCE) of 9.36% with an open-circuit voltage (Voc) of 0.88 V, a short-circuit current (Jsc) of 13.15 mA cm−2, and a fill factor (FF) of 0.67, under the illumination of AM 1.5G at 100 mW cm−2. The high PCE of this material combination could be attributed to its broad absorption spectrum and the high hole mobility (μh) and electron mobility (μe) of 9.56 × 10−4 and 5.17 × 10−4 cm2 V−1 s−1, respectively. These results indicate that the asymmetric electron-donating segments are promising to construct A-D-A type small molecular acceptors, which could largely enhance the diversity of building blocks to design photovoltaic materials.

Influence of molecular shape and interaction anisotropy on the self-assembly of tripod building blocks on solid surfaces

Molecular shape and directionality of intermolecular interactions are important factors which affect structure formation in adsorbed overlayers. In this contribution, using theoretical methods we demonstrate the importance of these factors in the surface-confined self-assembly of tripod-shaped organic molecules with reduced symmetry. To that end a lattice Monte Carlo model is proposed in which the molecules are represented in a coarse grained way, as flat rigid structures comprising a few connected segments adsorbed on a triangular lattice. The calculations are performed for the molecules equipped with terminal active centers providing directional intermolecular interactions. These results are compared with analogous data obtained for C3-symmetric units and Y-shaped molecules whose all composite segments are active. The simulated results show that for the directional interactions, the reduction of molecular symmetry leads to the formation of disordered, glassy, porous networks with hexagonal nanovoids of different shapes. Moreover, it is demonstrated that the interaction mode involving all molecular segments of the asymmetric building blocks is responsible for the formation of compact patterns. Relative thermal stability of the simulated assemblies is also compared, highlighting deciding role of the interaction mode in stabilization of the adsorbed superstructures. The findings of our theoretical investigations can be helpful in designing new molecular blocks and programming their interactions to create 2D molecular superstructures with tunable morphology and functions.

A random donor polymer based on an asymmetric building block to tune the morphology of non-fullerene organic solar cells

The introduction of an asymmetric unit enables a fine-tuned morphology and thus up to 10.4% efficiency for non-fullerene organic solar cells.

Effect of fluorination and symmetry on the properties of polymeric photovoltaic materials based on an asymmetric building block

Introducing fluorine on benzothiadiazole unit significantly influenced the properties of DTPa and BTs based conjugated polymers by tuning the energy levels and symmetry of the building blocks.

Halide ion-driven self-assembly of Zn(ii) compounds derived from an asymmetrical hydrazone building block: a combined experimental and theoretical study

Self-assembly of Zn(ii) compounds is influenced by a counter ion and non-covalent interactions.

The chaperone αB-crystallin uses different interfaces to capture an amorphous and an amyloid client.

Small heat-shock proteins, including αB-crystallin (αB), play an important part in protein homeostasis, because their ATP-independent chaperone activity inhibits uncontrolled protein aggregation. Mechanistic details of human αB, particularly in its client-bound state, have been elusive so far, owing to the high molecular weight and the heterogeneity of these complexes. Here we provide structural insights into this highly dynamic assembly and show, by using state-of-the-art NMR spectroscopy, that the αB complex is assembled from asymmetric building blocks. Interaction studies demonstrated that the fibril-forming Alzheimer's disease Aβ1-40 peptide preferentially binds to a hydrophobic edge of the central β-sandwich of αB. In contrast, the amorphously aggregating client lysozyme is captured by the partially disordered N-terminal domain of αB. We suggest that αB uses its inherent structural plasticity to expose distinct binding interfaces and thus interact with a wide range of structurally variable clients.