Timoshenko beam model for chiral materials

Natural and artificial chiral materials such as deoxyribonucleic acid （DNA）, chromatin fibers, flagellar filaments, chiral nanotubes, and chiral lattice materials widely exist. Due to the chirality of intricately helical or twisted microstructures, such materials hold great promise for use in diverse applications in smart sensors and actuators, force probes in biomedical engineering, structural elements for absorption of microwaves and elastic waves, etc. In this paper, a Timoshenko beam model for chiral materials is developed based on noncentrosymmetric micropolar elasticity theory. The governing equations and boundary conditions for a chiral beam problem are derived using the variational method and Hamilton＇s principle. The static bending and free vibration problem of a chiral beam are investigated using the proposed model. It is found that chirality can significantly affect the mechanical behavior of beams, making materials more flexible compared with nonchiral counterparts, inducing coupled twisting deformation, relatively larger deflection, and lower natural frequency. This study is helpful not only for understanding the mechanical behavior of chiral materials such as DNA and chromatin fibers and characterizing their mechanical properties, but also for the design of hierarchically structured chiral materials.

Chiral multiple-resonance thermally activated delayed fluorescence materials based on chiral spiro-axis skeleton for efficient circularly polarized electroluminescence

Chiral luminescence materials have potential applications in the field of three-dimensional displays due to their circularly polarized luminescence(CPL)characteristics.However,the further development of circularly polarized organic light-emitting diodes(CP-OLEDs)needs to meet the requirements of high efficiency,high color purity,low cost,and high dissymmetry factor(gPLor gEL),chiral multiple resonance thermally activated delayed fluorescence(MR-TADF)materials are considered as candidates in these aspects.Herein,based on a pair of chiral spirofluorene precursors,two pairs of high-performance chiral MR-TADF emitters((R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB)are developed,which exhibit strong emissions peaking at 491 and 502 nm in toluene with full-width at half-maximum values of 25 and 33 nm,respectively.In addition,small singlet–triplet energy gaps of 0.15 and 0.10 eV with high absolute photoluminescence efficiencies of 95.0%and 96.7%are observed for p-Spiro-DtBuCzB and m-Spiro-DtBuCzB molecules,respectively.OLEDs based on p-Spiro-DtBuCzB and m-Spiro-DtBuCzB display high maximum external quantum efficiencies of 29.6%and 33.8%,respectively.Most importantly,CP-OLEDs present symmetric circularly polarized electroluminescence spectra with|gEL|factors of 3.36×10^(-4)and 7.66×10^(-4)for devices based on(R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB enantiomers,respectively.

Chiral thermally activated delayed fluorescence materials for circularly polarized organic light-emitting diodes

Chirality is an important natural characteristic of organic molecules,and chiral organic molecules have shown extensive application in areas such as pharmaceutical development and material science.Benefiting from the ability to achieve circularly polarized luminescence(CPL),chiral luminescent materials have shown potential applications in anti-glare display,optical communication and,3D display,etc.Due to the ability to harvest both singlet and triplet excitons by a fast reverse intersystem crossing process without involving noble metals,chiral thermally activated delayed fluorescence(TADF)materials with point chirality,axial chirality,planar chirality and helical chirality are regarded as the state-of-the-art materials for circularly polarized organic light-emitting diodes(CP-OLEDs).In recent years,the chiral TADF materials and CP-OLEDs have rapidly developed,but unfortunately,the dissymmetry factors(g)are far from the requirement of practical applications.The ideal emitters and devices should have both high efficiency and a g factor,or at least a balance between these two elements.This review gives an overview of recent progress in chiral TADF materials,with a particular focus on the chiral skeleton,CPL property and device performance.Furthermore,the molecular design concept,device structure and methods to improve the g factors of chiral materials and CP-OLEDs are also discussed.

Determination of multilevel chirality in nickel molybdate films by electron crystallography

Chiral inorganic materials have attracted great attention owning to their unique physical and chemical properties attributed to the symmetry-breaking of their nanostructures.Chiral inorganic materials can be endowed with chiral geometric configurations from achiral space group crystals through lattice twisting,screw dislocations or hierarchical self-assembled spiral morphologies,showing various characteristic chiral anisotropy.However,the multilevel chirality in chiral nickel molybdate films(CNMFs)remains to be elaborately excavated.In this paper,we report three hierarchical levels of chirality in CNMFs,spanning from the atomic to the micron scale,including primary helically coiled nanoflakes with twisted atomic crystal lattices,secondary helical stacking of layered nanoflakes,and tertiary asymmetric morphology between adjacent nanoparticles.Our findings may enrich the chiral self-assembly structural types and provide valuable insights for the comprehensive analysis path of hierarchical chiral crystals.

Research Advances in Helicene Structure-Based Chiral Luminescent Materials and Their Circularly Polarized Electroluminescence

Benefited from direct generation of circularly polarized(CP) emission with tunable colors, high efficiencies and facile device architectures, CP organic light-emitting diodes(CP-OLEDs) have attracted great attention and are expected to meet industrial applications. Particularly, CP electroluminescence(CPEL) originated from CP-OLEDs has wide potential applications in 3D displays, optical information storage, quantum communication, and biological sensors. The diverse design strategies of chiral luminescent materials for CP-OLEDs, including small organic emitters, lanthanide and transition-metal complexes and conjugated polymers, have been extensively explored. Helicene with twisted extended π-conjugated molecular structure could exhibit special helical chirality and excellent circularly polarized luminescence properties, which has been employed as the ingenious chirality core for constructing efficient chiral luminescent materials. In addition, significant improvements have been made in terms of CP photoluminescence research, however, the development of CPEL with more application prospects in optoelectronic technology still lags behind. In this review, we systematically summarize the recent advances in chiral luminescent materials based on helicene structure and their CPEL properties, including helicene-based chiral fluorescence molecules, transition metal complexes and thermally activated delayed fluorescence molecules, and discuss current challenges and future perspectives for this hot research field. We believe this progress report will provide a promising perspective of OLEDs based on helicene emitters with CPEL properties for extensive researchers, including chemical, physical and material scientists in different disciplinary fields and attract them to this rapidly developing field.

Color-tunable circularly polarized electroluminescence from a helical chiral multiple resonance emitter with B–N bonds

Chiral B,N-doped polycyclic aromatic hydrocarbons with circularly polarized luminescence(CPL) and small full-width at halfmaxima(FWHM) are promising multiple resonance(MR) emitters for CP organic light-emitting diodes(CP-OLEDs).This work presents a pair of chiral MR enantiomers,P/M-o[B-N]_(2)N_(2),featuring B–N bonds incorporated within a[7]-helicene skeleton.These enantiomers exhibit narrow 0-0 and 0-1 electronic transition bands,whose relative intensity can be fine-tuned by increasing doping concentrations,resulting in redshifts of the emission peak from 542 to 592 nm.The enantiomers show mirrorsymmetric CPL spectra with an asymmetry factor(|g_(PL)|) of 1.0×10^(-3).The hyperfluorescent CP-OLEDs with double-sensitized emitting layers display a FWHM of 33 nm,an external quantum efficiency of 25.1%,and a|g_(EL)|factor of 7.7×10^(-4).Notably,the CP-OLEDs realize color-tunable CP electroluminescence peak from 553 to 613 nm by regulating the vibrational coupling.This work provides a novel concept for the design of helical CP-MR materials and CP-OLEDs,highlighting their potential for future applications in advanced optoelectronic devices.

Frontiers in circularly polarized luminescence:molecular design,self-assembly,nanomaterials,and applications

The research in circularly polarized luminescence has attracted wide interest in recent years.Efforts on one side are directed toward the development of chiral materials with both high luminescence efficiency and dissymmetry factors,and on the other side,are focused on the exploitations of these materials in optoelectronic applications.This review summarizes the recent frontiers(mostly within five years)in the research in circularly polarized luminescence,including the development of chiral emissive materials based on organic small molecules,compounds with aggregation-induced emissions,supramolecular assemblies,liquid crystals and liquids,polymers,metal-ligand coordination complexes and assemblies,metal clusters,inorganic nanomaterials,and photon upconversion systems.In addition,recent applications of related materials in organic light-emitting devices,circularly polarized light detectors,and organic lasers and displays are also discussed.

Handedness-inverted polymorphic helical assembly and circularly polarized luminescence of chiral platinum complexes

Circularly polarized luminescence(CPL)materials have potential applications in three-dimensional(3D)displays,quantum encryption,and optical sensors.The development of single-component CPL materials with polymorphic assembly and handedness inversion remains a significant challenge.Herein,we present the access of such materials by controlling the underlying assembly pathway of well-designed chiral emitters.A pair of enantiomeric platinum complexes(R)-1 and(S)-1 decorated with a chiralα-methylbenzyl isocyanide ligand were prepared.By using the mixed-solvent(THF/n-hexane,THF=tetrahydrofuran)or high-concentration condition,these complexes were found to assemble via a cooperative or isodesmic pathway with significantly enhanced yellow or red emission,respectively.The aggregate samples obtained via these conditions show efficient CPL(dissymmery factor|glum|>0.02,emission quantum yieldΦ>20%).Interestingly,different assembly pathway leads to helical nanoribbons or nanofibers with opposite handedness from the complex with the same molecular chirality.This has been unambiguously and consistently manifested by circular dichroism and CPL spectral analysis and transmission electron,scanning electron,and atomic force microscope studies.This work demonstrates an appealing example of constructing polymorphic helical architectures with highly efficient CPL and inverted handedness thanks to the excellent assembly and emission of platinum complexes.

Propagation of Electromagnetic Waves in Slab Waveguide Structure Consisting of Chiral Nihility Claddings and Negative-Index Material Core Layer

The dispersion equation of an asymmetric three-layer slab waveguide, in which all layers are chiral materials is presented. Then, the dispersion equation of a symmetric slab waveguide, in which the claddings are chiral materials and the core layer is negative index material, is derived. Normalized cut-off frequencies, field profile, and energies flow of right-handed and left-handed circularly polarized modes are derived and plotted. We consider both odd and even guided modes. Numerical results of guided low-order modes are provided. Some novel features, such as abnormal dispersion curves, are found.

Optically Ambidextrous Reflection and Luminescence in Self-Organized Left-Handed Chiral Nematic Cellulose Nanocrystal Films

Defect-embedded chiral nematic organizations are attractive due to their light manipulation ability that is crucial for photonic applications.Self-assembly of cellulose nanocrystals(CNC)forms a left-handed chiral nematic structure,which makes simultaneous reflection of left-handed circularly polarized(LCP)and right-handed circularly polarized(RCP)light a challenging task.Herein,we present unprecedented evidence that self-organized CNC films with left-handed helical sense and photonic bandgaps(PBG)display ambidextrous CP light reflection with peak reflectivity up to 68%and transform spontaneous photoluminescence to RCP and LCP luminescence with respective|glum|values up to 0.796 and 0.120.These ambidextrous chiroptical properties originate from a left-handed chiral nematic structure consisting of a nematic-like phase,acting as a half-wave retarder,sandwiched between two PBG layers.The latter are spontaneously intercalated into the left-handed helicoids by rapid gelation of CNC colloidal suspensions.We demonstrate that the ambidextrous chiroptical properties can be manipulated by changes in evaporation temperatures,concentrations,and characteristics of CNC suspensions.We showcase the potential of defect-embedded chiral nematic CNC films for the sustainable and scalable development of anti-counterfeiting optical labels.

Chiral pillar[n]arenes:Conformation inversion,material preparation and applications

Chiral pillar[n]arenes have shown great research value and application prospect in construction of chiral materials and chiral applications,due to their inherent planar chiral configurations,chiral recognition ability,easy modification and highly symmetric hydrophobic cavity.This review systematically summarized the conformation inversion factors of planar chiral pillar[5]arenes(pR/p S),such as solvents,temperature,substituent size,alkyl chains,chiral and achiral guest molecules.We firstly introduced the applications of chiral pillar[n]arenes for constructing chiral materials and pointed out that planar conformation inversion showed a great potential role in constructing chiral materials.Then,we mainly concluded the chiral applications of chiral and planar chiral pillar[n]arenes like chiral enantiomer analysis by circular dichroism,electrochemistry or chiral fluorescence sensing.From this review,we found that the inherent planar chiral conformation of chiral pillar[n]arenes have played a very important role in chiral field in the future.

兼具超长有机磷光和强圆偏振发光性质的蓝光轴手性材料

本文报道了一类兼具超长有机磷光(UOP)和强圆偏振发光(CPL)性质的蓝光轴手性材料.这类材料不仅具有极小的单重态(S1)-三重态(T1)能隙差(ΔE_(ST),0.03 eV),能够极大地促进系间窜越过程以产生更多的三重态激子,而且还具有超长的磷光衰减寿命(5.5 s).因此,这类材料在77 K下的2-MeTHF稀溶液中显示长达60 s的亮蓝色余辉.我们进一步提出了“激子沙漏”模型来描述内部的光物理过程和解释产生超长余辉的原因.此外,由于刚性的轴手性骨架,这类UOP材料还表现出强的CPL活性,尤其是将它们用作液晶材料的手性诱导剂时,能够获得0.34的g_(lum)值.本工作对于进一步设计兼具UOP和强CPL性质的新型纯有机分子材料具有重要的指导意义.

Dual photopatterning of rotational fingerprint superstructures

Controlling architecture of hierarchical microstructures in liquid crystals(LCs]plays a crucial role in the development of novel soft-matter-based devices.Chiral LC fingerprints are considered as a prospective candidate for various applications;however,the efficient and real-time command of fingerprint landscapes still needs to be improved.Here,we achieve elaborate rotational fingerprint superstructures via dual photopatterning semifree chiral LC films,which combine the photoalignment technique and a dynamic light patterning process.An intriguing spatial-temporal rotational behavior is presented during the patterning of chiral superstructures.This work opens new avenues for the applications of chiral LCs in soft actuators,sensing,and micromanufacturing.