Supramolecular Chirality in Achiral Polyfluorene: Chiral Gelation, Memory of Chirality, and Chiral Sensing Property

Precise Modulation of Circularly Polarized Luminescence via Polymer Chiral Co-assembly and Contactless Dynamic Chiral Communication

Circularly polarized luminescence (CPL) plays a pivotal role in cutting-edge display and information technologies. Currently achieving precise color control and dynamic signal regulation in CPL still remains challenging due to the elusory relationship between fluorescence and chirality. Inspired by the natural mechanisms governing color formation and chiral interaction, we proposed an addition-subtraction principle theory to address this issue. Three fluorene-based polymers synthesized by Suzuki polycondensation with different electron-deficient monomers exhibit similar structures and UV/Vis absorption, but distinct fluorescence emissions due to intramolecular charge transfer. Based on this, precise-color CPL-active films are obtained through quantitative supramolecular co-assembly directed by addition principle. Particularly, an ideal white-emitting CPL film (CIE coordinates: (0.33, 0.33)) is facilely fabricated with a high quantum yield of 80.8 % and a dissymmetry factor (glum) of 1.4×10-2. Structural analysis reveals that the ordered stacking orientation favors higher glum. Furthermore, to address the dynamically regulated challenge, the comparable subtraction principle is proposed, involving a contactless chiral communication between excited and ground states. The representative system consisting of as-prepared fluorene-based polymers and chirality-selective absorption azobenzene (Azo)-containing polymers is constructed, achieving CPL weakening, reversal, and enhancement. Finally, a switchable quick response code is realized based on trans-cis isomerization of Azo moiety.

Using a molecular additive to control chiral supramolecular assembly and the subsequent chirality transfer process

Hierarchical assembly of chiral molecules is achieved through the introduction of molecular additives, which enables the chiral assembly of nanosheets into helical nanorods with inverted chirality. Moreover, the hierarchical assembly of chiral molecules in the presence of a molecular additive can lead to the subsequent chirality transfer from a molecular system to nanoparticle assemblies.

Enantioselective and Chemoselective Optical Detection of Chiral Organic Compounds without Resorting to Chromatography

Enantiorecognition and resolution are of essential importance in many diverse areas of science. Whenever there arises a need to analyze/investigate enantiomers in different situations chromatography stands up in our minds immediately. Nevertheless, chemoselective and enantioselective recognition/discrimination (without going for separation) constitutes a different perception and requirement. The techniques using chiroptical sensing cause detection based on molecular interactions induced in different manners. Enantioselective sensing of monosaccharides in γ-cyclodextrin assembly and by diboronic acid based fluorescent sensors, application of bi-naphthol and H8 BINOL based sensors and dendrimers, metal-to-ligand charge transfer transitions in CD, exciton-coupled circular dichroism, surface enhanced Raman spectroscopy, and enantioselective indicator displacement sensor arrays for enantioselective recognition/detection of chiral organic compounds, such as amines, amino acids/alcohols, and hydroxycarboxylic acids have been discussed in progressive manner with mechanistic explanations, wherever available. Besides, the chiroptical vs LC approach has been discussed. The present paper is focused on certain different non-chromatographic optical techniques and aims to extend an understanding and a view to consider such techniques which have been successful in selective detection, and determination of absolute configuration and enantiomeric excess, (without resorting to separation vis-à-vis LC) and that have potential use in high-throughput chiral assay and combinatorial search for asymmetric catalysts and reagents.

Dynamic monitoring of self-assembly by confining conformational changes of butterfly-motion-based molecules

A simple dynamic monitoring strategy for chiral self-assembly is achieved by confining the bent-to-planar evolution observed in N,N'-diphenyl-dihydrodibenzo[a,c]phenazine derivatives (DPAC-R/S-GLD). Besides, this approach provides a facile pathway to fabricate architectures with circularly polarized luminescence (CPL) properties.

Helical Polymer Working as a Chirality Amplifier to Generate and Modulate Multicolor Circularly Polarized Luminescence in Small Molecular Fluorophore/Polymer Composite Films

In-depth studies of chirality and circularly polarized luminescence (CPL) have become indispensable in the process of learning human nature. Small molecules with CPL activity are one of the research hotspots. However, the CPL properties of such materials are generally not satisfying. Here, we synthesized a series of chiral small molecular fluorophores that cannot demonstrate CPL emission themselves. By introducing an optically inactive helical polymer, chirality transfer and chirality amplification efficiently occur, thereby generating intense CPL emission. Through combining different chiralized fluorophores, multicolor CPL-active films with emission wavelength centered at 463, 525, and 556 nm were fabricated, with the maximum luminescence dissymmetry factor (g_lum) being up to -0.028. Then, benefiting from the strong CPL emission and appropriate energy donor-acceptor system, we further established a circularly polarized fluorescence-energy transfer (CPF-ET) strategy in which the CPL-active films work as a donor emitting circularly polarized fluorescence to excite an achiral fluorophore (Nile red) as the acceptor, producing red CPL with g_lum of up to -0.011 at around 605 nm.

Self-recovery of chiral microphase separation in an achiral diblock copolymer system

Macroscopic regulation of chiral supramolecular nanostructures in liquid-crystalline block copolymers is of great significance in photonics and nanotechnology. Although fabricating helical phase structures via chiral doping and microphase separation has been widely reported, the chiral memory and self-recovery capacity of asymmetric phase structures are the major challenge and still deeply rely on the presence of chiral additives. Herein, we demonstrate the first controllable chiral microphase separation in an achiral amphiphilic block copolymer consisting of poly(ethylene oxide) and azobenzene (Azo) groups. Chirality can be transferred to the fabricated helical nanostructures by doping with chiral additives (tartaric acid, TA). After the removal of the chiral additives and then performing cross-linking, the formed helical nanostructures will completely dispense with the chiral source. The supramolecular chirality and the micron-scale phase structure can be maintained under UV irradiation and heating-cooling treatment, enabling a reversible "on-off" chiroptical switch feature. This work is expected to avoid the tedious synthesis and expensive raw materials and shows a great application prospect in chiral separation and so on.

Chiral Recognition with Broad Selective Sensor Arrays

The detection and discrimination of chiral analytes has always been a topical theme in food and pharmaceutical industries and environmental monitoring, especially when dealing with chiral drugs and pesticides, whose enantiomeric nature assessment is of crucial importance. The typical approach matches novel chiral receptors designed ad hoc for the discrimination of a target enantiomer with emerging nanotechnologies. The massive synthetic efforts requested and the difficulty of analyzing complex matrices warrant the ever-growing exploitation of sensor array as an alternative route, using a limited number of chiral or both chiral and achiral sensors for the stereoselective identification and dosing of chiral compounds. This review aims to illustrate a little-explored winning strategy in chiral sensing based on sensor arrays. This strategy mimics the functioning of natural olfactory systems that perceive some couples of enantiomeric compounds as distinctive odors (i.e., using an array of a considerable number of broad selective receptors). Thus, fundamental concepts related to the working principle of sensor arrays and the role of data analysis techniques and models have been briefly presented. After the discussion of existing examples in the literature using arrays for discriminating enantiomers and, in some cases, determining the enantiomeric excess, the remaining challenges and future directions are outlined for researchers interested in chiral sensing applications.

ATP-Induced Emergent Circularly Polarized Luminescence and Encryption

Biomimetic ATP-driven supramolecular assembly is important to understand various biological processes and dissipative systems. Here, we report an ATP-driven chiral assembly exhibiting circularly polarized luminescence (CPL) via the interaction of an achiral terpyridine-based Zn^II complex with nucleotides. It was found that while the metal complexes could co-assemble with the nucleotides to form fluorescent assemblies, only a combination of furan-substituted terpyridine complex and ATP showed an intense CPL with a dissymmetry factor (g_lum ) as high as 0.20. This means that the complex could recognize ATP using CPL as a readout signal, thus providing an example of ATP encryption. Interestingly, when ATP was transferred into ADP or AMP under enzymatic hydrolysis, the CPL decreases or disappears. Addition of ATP generates CPL again, thus producing an ATP-induced CPL system. This work presents the first example of ATP-induced CPL and encryption.

Building Permanently Optically Active Particles from Absolutely Achiral Polymer

Chirality in polymer particles represents one of the most dynamic areas of nanoscale materials today. The chirality of most chiral polymeric particles (CPPs) derived from achiral monomers/polymers has a strong...

CPL on/off control of an assembled system by water soluble macrocyclic chiral sources with planar chirality

Herein, we report the synthesis and planar chiral properties of a pair of water-soluble cationic pillar[5]arenes with stereogenic carbons. Interestingly, although units of the molecules were rotatable, only one planar chiral diastereomer existed in water in both cases. As a new type of chiral source, these molecules transmitted chiral information from the planar chiral cavities to the assembly of a water-soluble extended π-conjugated compound, affording circularly polarized luminescence (CPL). The chirality transfer process and resulting CPL were extremely sensitive to the feed ratio of the chiral pillar[5]arenes owing to the combined action of their planar chirality, bulkiness, and strong binding properties. When a limited amount of chiral source was added, further assembly of the extended π-conjugated compound into helical fibers with CPL was triggered. Unexpectedly, larger amounts of chiral source destroyed the helical fiber assemblies, resulting in elimination of the chirality and CPL properties from the assembled structures.

Readily obtained pillar[5]arenes with pure planar chirality enabled CPL on/off control of an assembled system by varying the feed ratio.

Engineering Achiral Liquid Crystalline Polymers for Chiral Self-Recovery

Flexible construction of permanently stored supramolecular chirality with stimulus-responsiveness remains a big challenge. Herein, we describe an efficient method to realize the transfer and storage of chirality in intrinsically achiral films of a side-chain polymeric liquid crystal system by combining chiral doping and cross-linking strategy. Even the helical structure was destroyed by UV light irradiation, the memorized chiral information in the covalent network enabled complete self-recovery of the original chiral superstructure. These results allowed the building of a novel chiroptical switch without any additional chiral source in multiple types of liquid crystal polymers, which may be one of the competitive candidates for use in stimulus-responsive chiro-optical devices.

Transfer, Amplification, Storage, and Complete Self-Recovery of Supramolecular Chirality in an Achiral Polymer System

Supramolecular chirality and its complete self-recovery ability are highly mystical in nature and biological systems, which remains a major challenge today. Herein, we demonstrate that partially cross-linked azobenzene (Azo) units can be employed as the potential chiral trigger to fully heal the destroyed helical superstructure in achiral nematic polymer system. Combining the self-assembly of Azo units and terminal hydroxyl groups in polymer side chains allows the vapor-induced chiral nematic phase and covalent fixation of the superstructure via acetal reaction. The induced helical structure of Azo units can be stored by inter-chain cross-linking, even after removal of the chiral source. Most interestingly, the stored chiral information can trigger perfect chiral self-recovery (CSR) behavior after being destroyed by UV light, heat, and solvents. The results pave a new way for producing novel chiroptical materials with reversible chirality from achiral sources.

Blending as a Strategy to Attain Chiro-Optically Activity Polymers

Two copolymers, one containing a chiral center and another without any asymmetric site are studied regarding their chiro-optical properties. The pure polymers do not show any signal of chiro-optical activity, only a smooth line is observed in the circular dichroism spectra, even for the chiral material. However, blends containing the achiral one as a major component show striking chiro-optical activity, originating by stable supramolecular structures whose size and shape remain unchanged, regardless of the blend composition. Only the number of such structures (composed by the chiral one), vary with blend composition. The results suggest that working with supramolecular morphology can be an important strategy to attain chiro-optical active polymers.

Switchable Circularly Polarized Luminescence in Supramolecular Gels through Photomodulated FRET

While the tremendous deal of efforts has been dedicated to the design and fabrication of materials with circularly polarized luminescence (CPL), the development of the chiroptical switch between different CPL signals is one of the important routes toward its application. Here, we prepared a supramolecular gel from the coassemblies containing a chiral gelator (9-fluoren-methoxycarbonyl-functionalized glutamate derivatives, FLG), a fluorescent molecule [(rhodamine B, RhB) or (2',7'-dichlorofluorescein sodium salt, DCF)], and a photochromic molecule [1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene, DAE], thus constructing photomodulated switchable CPL soft materials. It was found that FLG could form supramolecular gel in ethanol and self-assemble into left-handed twisted nanostructures. During the formation of a co-gel with RhB (or DCF) and DAE, the chirality of FLG could be effectively transferred to both the fluorescent and photochromic components, which induced them with chiroptical properties including CPL and circular dichroism (CD). DAE undergoes a reversible transition between the achromatous open state and the dark purple closed state in the co-gel under alternating irradiation with UV and visible light. During such a process, an intermolecular Förster resonance energy transfer (FRET) behavior from fluorescent RhB to ring-closed DAE caused the emission quenching of RhB, which led to CPL silence of RhB in the co-gel. Subsequent irradiation with visible light caused the restoration of the emission and CPL activity with the restored open state. These changes could be repeated many times upon alternate UV and visible irradiation. Therefore, a reversible CPL switch was fabricated in supramolecular gels through the photomodulated FRET process.

Supramolecular Chirality Suppresses Molecular Chirality: Selective Chiral Recognition in Hierarchically Coassembled Pyridine-Benzimidazole Conjugates with Precise ee% Detection

Incorporation of aromatic chiral species with axial, helical, or propeller chirality in surapmolecular chiral motifs would potentially facilitate the chiroptical applications such as enantiomeric excess detection, chiral sensing, and displays, which however suffer from inevitable competition between supramolecular chirality and molecular chirality and remain major challenges. Here, we show the programmable coassembly of pyridine-cored benzimidazole derivatives with intrinsic propeller chirality, which shall form binary and ternary aggregates with chiral acids as well as metal ions though H-bonds and metal-ligand coordination interactions in an orthogonal manner, to enhance and flexibly control the chiroptical properties. Solid-state X-ray structures of pyridine-benzimidazole derivatives suggested they adopted the propeller molecular chirality. Competition between molecular and supramolecular chirality and dynamic binding toward enantiomers of pyridine-benzimidazole derivatives was observed in the coassembly systems based on the chiroptical responses and molecular dynamic simulation. Compared to the intrinsic racemic assembly, coassembly systems produced chiroptical responses including the Cotton effect and circularly polarized luminescence (CPL) with relatively high dissymmetry factor (g_abs up to 4.9 × 10^-2, g_lum up to 9.6 × 10^-3). Furthermore, chiroptical responses were further controlled by introducing metal ions, achieving inverted handedness and tunable dissymmetry factors. This work provides feasible strategies to efficiently regulate and enhance the chiroptical properties of intrinsic aromatics via multiple interactions, which also expressed great potential in quantitative ee% sensing for chiral acids.

Molecular-level insights into the self-assembly driven enantioselective recognition process

The importance of the orientation of functional groups in a chiral environment on enantioselective recognition has been demonstrated. Orientation controlled interactions of functional groups in (R)/(S)-MA lead to a visually differentiable morphology with an arginine-based gelator. The crucial role of various molecular-level interactions discriminating the enantioselective self-assembly has been established using different analytical techniques, crystal structure analysis, and DFT calculations.

Induction of Chirality in Supramolecular Coassemblies Built from Achiral Precursors

The emergence, transference, amplification, and memory of chiroptical activity in supramolecular assemblies, including circularly polarized absorbance and circularly polarized luminescence, remain significant challenges. Herein, an achiral pyridine-substituted coumarin derivative and chiral additives can coassemble into helical nanostructures with fine chiroptical activity via subtle hydrogen-bonding interactions. The resulting supramolecular assemblies remain optically active even after the removal of chiral additives, demonstrating supramolecular chirality can be remembered in the assemblies. More importantly, the removed chiral elements can be reused to achieve continuous circulation and amplification of chirality. This work presents insight into the emergence, transference, amplification, and memory of chirality in a supramolecular assembly system and could be applied to the manufacturing of chiroptical materials.

Helical polymer self-assembly and chiral nanostructure formation

This review surveys recent progress towards robust chiral nanostructure fabrication techniques using synthetic helical polymers, the unique inferred properties that these materials possess, and their intricate connection to natural, biological chirality.

Induction, fixation and recovery of self-organized helical superstructures in achiral liquid crystalline polymer

A flexible chiral storage based on an achiral polymer system can be successfully achieved by chiral doping and covalent cross-linking.

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (g_abs and g_lum) and on the application of ECD and CPL to derive structural information on aggregated states.

Supramolecular Chirality in Azobenzene-Containing Polymer System: Traditional Postpolymerization Self-Assembly Versus In Situ Supramolecular Self-Assembly Strategy

Recently, the design of novel supramolecular chiral materials has received a great deal of attention due to rapid developments in the fields of supramolecular chemistry and molecular self-assembly. Supramolecular chirality has been widely introduced to polymers containing photoresponsive azobenzene groups. On the one hand, supramolecular chiral structures of azobenzene-containing polymers (Azo-polymers) can be produced by nonsymmetric arrangement of Azo units through noncovalent interactions. On the other hand, the reversibility of the photoisomerization also allows for the control of the supramolecular organization of the Azo moieties within polymer structures. The construction of supramolecular chirality in Azo-polymeric self-assembled system is highly important for further developments in this field from both academic and practical points of view. The postpolymerization self-assembly strategy is one of the traditional strategies for mainly constructing supramolecular chirality in Azo-polymers. The in situ supramolecular self-assembly mediated by polymerization-induced self-assembly (PISA) is a facile one-pot approach for the construction of well-defined supramolecular chirality during polymerization process. In this review, we focus on a discussion of supramolecular chirality of Azo-polymer systems constructed by traditional postpolymerization self-assembly and PISA-mediated in situ supramolecular self-assembly. Furthermore, we will also summarize the basic concepts, seminal studies, recent trends, and perspectives in the constructions and applications of supramolecular chirality based on Azo-polymers with the hope to advance the development of supramolecular chirality in chemistry.

Learning how planarization can affect dichroic patterns in polyfluorenes

The circular dichroism spectra of a single chain of polyfluorene was predicted for a p-twisted helix conformation and local planarized polymer sections in the presence and in the absence of thermal vibrations. Under thermal vibrations at 300 K, the planarized section of polyfluorene affords a red-shifted positive dichroic band between 446 and 456 nm, preserving a degree of chirality. The S1 ← S0 excitation energy decreases from 3.29 eV, for the p-twisted helix to 2.77 or 2.71 eV, for planarized sections with one or two coplanar twists, respectively. Thermal vibrations and intramolecular rotations eventually affect the circular dichroism spectrum patterns, where planarized bent conformers induce a positive band towards 450 nm.

Chiral helical polymer materials derived from achiral monomers and their chiral applications

Helix-sense-selective polymerization (HSSP) of achiral monomers and chiral post-induction of racemic helical polymers provide two alternative approaches for constructing chiral helical polymer materials.

Photo-controlled chirality transfer and FRET effects based on pseudo[3]rotaxane

The use of light to regulate the chirality of supramolecular assemblies in a non-invasive manner remains a challenge. Herein, we report a novel photochromic pseudo[3]rotaxane based on a (R/S)-2,2'-binaphthyl secondary ammonium salt guest (2) and anthracene-bridged bis(dibenzo-24-crown-8) (1), which features a chirality transfer and fluorescence resonance energy transfer (FRET) from 2 to 1. Benefiting from the photo-oxidation of anthracene, the induced circular dichroism (ICD) signals of (R/S)-2@1 can be switched off/on by irradiation with 365 nm UV light and heating. This noncovalent supramolecular assembly strategy provides us with unique opportunities to design and construct further smart photo-responsive chiral molecular switches.

Achiral isomers controlled circularly polarized luminescence in supramolecular hydrogels

Although chiral functional materials showing circularly polarized luminescence (CPL) are being widely reported, it remains a challenge to provide convenient and universal strategies for constructing controllable CPL-active materials with a high luminescence dissymmetry factor (glum). Herein, the supramolecular chirality as well as the CPL handedness of phenylalanine-based hydrogels can be effectively regulated by commercial achiral naphthylamine isomers through non-covalent interactions. Typically, the co-assembled hydrogels exhibit considerably high |glum| values in the range of 5.62 × 10-3-8.74 × 10-3. The CPL inversion is mainly facilitated by intermolecular hydrogen bonds and π-π stacking between the achiral and chiral molecules, which might be induced by the reorientations of the assembled molecules. This work may provide an alternative method to construct tunable CPL-active materials.

Dynamic Modulation of Supramolecular Chirality Driven by Factors from Internal to External Levels

Supramolecular chirality, generated by the asymmetric assembly of chiral or achiral molecules, has attracted intense study owing to its potential to offer insights into natural biological structures and its crucial roles in advanced materials. The optical activity and stacking pathway of building molecules both greatly determine the chirality of the whole supramolecular structure. The flexibility of supramolecular structures makes their chirality easy to modulate through abundant means. Adjustment of the molecular structure or packing mode, or external stimuli that act like a finger gently pushing toy bricks, can greatly change the chirality of supramolecular assemblies. The dynamic regulation of chiral nanostructures on the intramolecular, intermolecular, and external levels could be regarded as the modulatory essence in numerous strategies, however, this perspective is ignored in most reviews in the literature. Herein, therefore, we focus on the ingenious dynamic modulation of chiral nanostructures by these factors. Through dynamic modulation with changes in chiroptical spectroscopy and electron microscopy, the mechanism of formation of supramolecular chirality is also elaborated.

Switchable circularly polarized luminescence from a photoacid co-assembled organic nanotube

Materials with circularly polarized luminescence (CPL) are currently attracting great interest in view of their potential applications. Here, we reported self-assembled organic nanotubes with switchable CPL performance. A photoacid, 8-hydroxy-1,3,6-pyrenetrisulfonate (HPTS), was co-assembled with an amino-terminated dialkyl glutamide (LG or DG) in mixed solvents of DMF and water. The complex of LG (DG)/HPTS self-assembled into nanotube structures in the tested range of mixed solvents and showed CPL emission. Different mixing ratios of DMF to water in the solvent triggered CPL switching between different wavelengths. It was revealed that the switching of CPL resulted from the different emissions of the protonated (ROH) and deprotonated (RO-) forms of HPTS, which could be regulated by the solvent polarity. Interestingly, the addition of an acid or base could also switch the fluorescence of LG (DG)/HPTS co-assemblies and the corresponding CPL, leading to an acidity-regulated CPL switch. Thus, through a simple co-assembly strategy, switchable CPL was realized in the self-assembled organic nanotubes via both solvent polarity and acidity.

Сhiral and Racemic Fields Concept for Understanding of the Homochirality Origin, Asymmetric Catalysis, Chiral Superstructure Formation from Achiral Molecules, and B-Z DNA Conformational Transition

The four most important and well-studied phenomena of mirror symmetry breaking of molecules were analyzed for the first time in terms of available common features and regularities. Mirror symmetry breaking of the primary origin of biological homochirality requires the involvement of an external chiral inductor (environmental chirality). All reviewed mirror symmetry breaking phenomena were considered from that standpoint. A concept of chiral and racemic fields was highly helpful in this analysis. A chiral gravitational field in combination with a static magnetic field (Earth’s environmental conditions) may be regarded as a hypothetical long-term chiral inductor. Experimental evidences suggest a possible effect of the environmental chiral inductor as a chiral trigger on the mirror symmetry breaking effect. Also, this effect explains a conformational transition of the right-handed double DNA helix to the left-handed double DNA helix (B-Z DNA transition) as possible DNA damage.

Spreading Films of Anthracene-Containing Gelator Molecules at the Air/Water Interface: Nanorod and Circularly Polarized Luminescence

Two enantiomeric gelator molecules containing anthracene moiety were assembled at the air/water interface and several new insights into the films of the gelator molecules were revealed. When these molecules were spread at the air/water interface, they formed the nanorod structured monolayers and could be subsequently transferred to the solid substrate. The formed Langmuir-Blodgett (LB) films showed both optical activity and circularly polarized luminescence (CPL) due to the chirality transfer upon assembling. The dissymmetric factors of the CPL in the LB films were enhanced nearly 5 times than those in gel systems. Through the formation of the organized nanofilms, the arrangement of the molecules become compact and the film showed enantioselectivity to chiral species, whereas the molecular solution could not.

Optically active quantum dots with induced circularly polarized luminescence in amphiphilic peptide dendron hydrogel

In this study, water-soluble semiconductor quantum dots (QDs) showing induced circularly polarized luminescence (CPL) in an organic-inorganic coassembled hydrogel were demonstrated. Achiral QDs could be encapsulated into a chiral peptide dendron hydrogel through cogelation. These cogels displayed intense induced circularly polarized emission. In addition, the direction of the CPL property of QD cogels could be regulated by the supramolecular chirality of hydrogels. Our findings reveal that the emergence of CPL achiral QDs can be triggered by the chirality transfer in a multiple-component dendron hydrogel system. This study has given a new understanding into the design of functional chiroptical materials.

Aggregation-induced chiroptical generation and photoinduced switching of achiral azobenzene-alt-fluorene copolymer endowed with left- and right-handed helical polysilanes

The left and right helicities of azobenzene (Azo)-containing main-chain polymer (PF8Azo) were successfully controlled with an enantiomeric pair of rigid rod-like helical polysilanes carrying (S)- and (R)-2-methylbutyl groups (PSi-S and PSi-R, respectively) as their hetero-aggregates in a mixture of chloroform and methanol solvents and in the solid state. Optimizing the good and poor cosolvents and their volume fractions showed that the molar ratio of PF8Azo to PSi-S/-R and the molecular weight of PF8Azo were crucial to boost the CD amplitudes of PF8Azo/PSi-S and PF8Azo/PSi-R hetero-aggregates. The photoresponsive trans-cis transformation caused noticeable changes in the sign and magnitude of the chiroptical behavior due to the hetero-aggregates. Moreover, the optically active PF8Azo homo-aggregates were produced by complete photoscissoring reactions at 313 nm, which could be assigned to the Siσ-Siσ* transitions of PSi-S and PSi-R.

Chiral helical disubstituted polyacetylenes form optically active particles through precipitation polymerization

Preparation of optically active polymer particles constructed by chiral helical disubstituted polyacetylenes via precipitation polymerization.

The chiral amine triggered self-assembly of achiral emissive molecules into circularly polarized luminescent supramolecular assemblies

Enantiomeric diaminocyclohexane was found to trigger the self-assembly of achiral monomers into chiral supramolecular assemblies with strong circularly polarized luminescence.

Control over chiroptical and electronic properties of poly(9,9′-bifluorenylidene) bearing chiral side chains

The introduction of chiral side chains at peripheral positions of the 9,9′-bifluorenylidene moiety causes an efficient bias to its dynamic molecular helicity, which helps control the chiroptical and electronic properties of resultant polymers.

Different phase-dominated chiral assembly of polyfluorenes induced by chiral solvation: axial and supramolecular chirality

The introduction of chirality in an achiral system will not only help avoid the tedious and expensive synthesis of chiral substances or catalysts but also greatly expand the ranges of chiral compounds. Herein, the induction of chirality in achiral polyfluorene (PF2/6 and PF8) with different alkyl chains at the C9 position of fluorene was achieved using a binary solvent system, in which ethanol was used as a poor solvent and chiral limonene was employed simultaneously as a good solvent and chiral solvent. The circular dichroism (CD), UV-vis and photoluminescence (PL) spectra demonstrated that the structures of PFs with linear/branched alkyl side chains and the volume fractions of the cosolvents had an obvious effect on the generation of chirality driven by chiral solvation. During the chiral assembly processes of PFs, PF8 with a linear alkyl side chain demonstrated the obvious chiral β phase, while PF2/6 with a branched alkyl side chain only showed the chiral α phase. WAXD data also confirmed the existence of quite different phases of PF8 and PF2/6. The first induced chirality of PF with a branched alkyl side chain (PF2/6) will help the further understanding of the chiral assembly mechanism of PFs driven by chiral solvation. The induced chirality of PF2/6 was axial chirality of the PF chain but the chirality of PF8 was from the supramolecular chiral assembly of the PF chains. The linear dependence of the maximum CD and g_CD values on the enantiomeric purity of chiral limonene demonstrated that the achiral PFs have a potential application as chiral sensors to detect the ee value of limonene.

The chiral solvation induced chirality in achiral polyfluorenes showed the axial chirality for PF2/6 with branched side alkyl chain, but supramolecular chirality for PF8 with linear side alkyl chain.