Fabrication of Helical Nanoribbon Polydiacetylene via Supramolecular Gelation: Circularly Polarized Luminescence and Novel Diagnostic Chiroptical Signals for Sensing

A Universal Strategy for Reversible and Spatiotemporal Electrofluorochromism of Eu3+ Metallogels Driven by Cooperative Chemical Reactions with Biomimetic Information "Memorizing-forgetting" Behavior

Taking inspiration from the dynamic memory of the human brain, which has the ability to spontaneously forget unimportant information, a universal and straightforward method for creating spatiotemporally regulated hydrogels with electrofluorochromic characteristics that exhibit information "memorizing-forgetting" behavior is presented. The dynamic and reversible electrofluorochromism from blue to red  in Eu3+-based hydrogels is achieved by rapid changes in fluorescence triggered by electricity, coupled with the gradual disappearance of fluorescence associated with the mass diffusion ability of the hydrogel. This process involves the generation of H2 from an acidic aqueous solution under electricity, resulting in the conversion of β-diketone derivatives from keto to enol forms and the disruption of hydrogen bonds between ─COOH of polyacrylic acid (PAA) and N of pyridine groups. The dynamic fluorescent and mechanical behavior are facilely tuned by power on time, contents of components, and types of network structures as well as pyridine derivatives. Finally, the hydrogel arrays or films can be utilized for programmable and accurate information encryption, decryption, and self-erasure.

Biomolecule-functionalized polydiacetylene assembly for visual and on-site sensing of (E)-2-hexenal in fruits

(E)-2-Hexenal (E2H) is an important volatile organic compound (VOC) that can serve as a marker for fruit quality sensing and shelf-life evaluation. However, visual and portable sensors for E2H have not been reported mainly because of the difficulty in selective response to E2H while avoiding interference from other VOC, especially isomers. Herein, we developed a novel colorimetric sensor based on thiol-functionalized polydiacetylene assembly (PDA-SH/PDA) for the quantitative and selectivity of E2H. The mechanism was that E2H underwent a Michael addition reaction with sulfhydryl groups in PDA-SH/PDA. The Michael addition reaction destroyed the hydrogen bond and distorted the conjugated molecular system, resulting in colorimetric responses. Under optimal conditions, a good linear relationship was observed between E2H concentration and red colorimetric shift (R2 = 0.9679). The E2H sensor yields a high analytical sensitivity of 1.5203% and a limit of detection of 0.015 g L-1. Besides, the PDA-SH/PDA sensor can be used to visually distinguish E2H and its isomer (Z)-3-hexenal. The PDA-SH/PDA sensor yielded a statistically significant difference in red colorimetric shift (p < 0.01) between the pairs of isomers in the ripeness of fruits. At last, the sensor was utilized for detecting E2H in grapes from different shelf lives. We found that the E2H concentration increased from 66.16 ± 1.54 to 67.56 ± 1.30 µg L-1 as storage time was prolonged. The results of this research not only demonstrated the feasibility of visual and on-site detection of E2H but also provided potential promise for portable fruit quality sensing and shelf-life evaluation.

Macrocyclic Diacetylene / Sulfonate Fluorophore Hierarchical Multifunctional Nanotoroids

Functional supramolecular materials exhibit important features including structural versatility and versatile applications. Here, this study reports the construction of unique hierarchically organized nanotoroids exhibiting fluorescence, photocatalytic, and sensing properties. The nanotoroids comprise of macrocyclic diacetylenes (MCDA) and 8-anilino-1-naphthalene sulfonate (ANS), a negatively charged aromatic fluorescent dye. This study shows that the hierarchical structure of the nanotoroids consist of MCDA nanofibers formed by stacked diacetylene monomers as the basic units, which are further bent and aligned into toroidal organization by electrostatic and hydrophobic interactions with the ANS molecules. The amine moieties on the nanotoroids surface are employed for deposition of gold nanostructures - Au nanoparticles or Au nanosheets - which constitute effective platforms for photocatalysis and surface enhanced Raman scattering (SERS)-based sensing.

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Dual Enhancement of Phosphorescence and Circularly Polarized Luminescence through Entropically Driven Self-Assembly of a Platinum(II) Complex

Addressing the dual enhancement of circular polarization (glum) and luminescence quantum yield (QY) in circularly polarized luminescence (CPL) systems poses a significant challenge. In this study, we present an innovative strategy utilizing the entropically driven self-assembly of amphiphilic phosphorescent platinum(II) complexes (L-Pt) with tetraethylene glycol chains, resulting in unique temperature dependencies. The entropically driven self-assembly of L-Pt leads to a synergistic improvement in phosphorescence emission efficiency (QY was amplified from 15 % at 25 °C to 53 % at 60 °C) and chirality, both in the ground state and the excited state (glum value has been magnified from 0.04×10-2 to 0.06) with increasing temperature. Notably, we observed reversible modulation of phosphorescence and chirality observed over at least 10 cycles through successive heating and cooling, highlighting the intelligent control of luminescence and chiroptical properties by regulating intermolecular interactions among neighboring L-Pt molecules. Importantly, the QY and glum of the L-Pt assembly in solid state were measured as 69 % and 0.16 respectively, representing relatively high values compared to most self-assembled CPL systems. This study marks the pioneering demonstration of dual thermo-enhancement of phosphorescence and CPL and provides valuable insights into the thermal effects on high-temperature and switchable CPL materials.

Light-Induced Self-Assembled Polydiacetylene/Carbon Dot Functional "Honeycomb"

The design of functional supramolecular assemblies from individual molecular building blocks is a fundamental challenge in chemistry and material science. We report on the fabrication of "honeycomb" films by light-induced coassembly of diacetylene derivatives and carbon dots. Specifically, modulating noncovalent interactions between the carbon dots, macrocyclic diacetylene, and anthraquinone diacetylene facilitates formation of thin films exhibiting a long-range, uniform pore structure. We show that light irradiation at distinct wavelengths plays a key role in the assembly process and generation of unique macro-porous morphology, by both initiating interactions between the carbon dots and the anthraquinone moieties and giving rise to the topotactic polymerization of the polydiacetylene network. We further demonstrate utilization of the macro-porous film as a photocatalytic platform for water pollutant degradation and as potential supercapacitor electrodes, both applications taking advantage of the high surface area, hydrophobicity, and pore structure of the film.

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.

TiS3 Nanoribbons: A Novel Material for Ultra-Sensitive Photodetection across Extreme Temperature Ranges

Photodetectors that can operate over a wide range of temperatures, from cryogenic to elevated temperatures, are crucial for a variety of modern scientific fields, including aerospace, high-energy science, and astro-particle science. In this study, we investigate the temperature-dependent photodetection properties of titanium trisulfide (TiS₃)- in order to develop high-performance photodetectors that can operate across a wide range of temperatures (77 K-543 K). We fabricate a solid-state photodetector using the dielectrophoresis technique, which demonstrates a quick response (response/recovery time ~0.093 s) and high performance over a wide range of temperatures. Specifically, the photodetector exhibits a very high photocurrent (6.95 × 10^-5 A), photoresponsivity (1.624 × 10⁸ A/W), quantum efficiency (3.3 × 10⁸ A/W·nm), and detectivity (4.328 × 10¹⁵ Jones) for a 617 nm wavelength of light with a very weak intensity (~1.0 × 10^-5 W/cm²). The developed photodetector also shows a very high device ON/OFF ratio (~32). Prior to fabrication, the TiS₃ nanoribbons were synthesized using the chemical vapor technique and characterized according to their morphology, structure, stability, and electronic and optoelectronic properties; this was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and a UV-Visible-NIR spectrophotometer. We anticipate that this novel solid-state photodetector will have broad applications in modern optoelectronic devices.

Supramolecular Chiral Assembly of Symmetric Molecules with an Extended Conjugated Core

C3-symmetric molecules carrying a conjugated diacetylene (DA) core are found to self-assemble into well-defined supramolecular fibers with enhanced supramolecular chirality in both organic and aqueous solutions. The conjugated core affords these amphiphiles characteristic fluorescence properties, which can be quenched partially due to the aggregation. Integration of the C3-symmetry with the conjugation provides these novel molecules strong aggregation tendency through solvent-mediated π-π stacking with preferential supramolecular chirality, which is predominately related to steric hindrance from their dipeptide pendants. Highly uniform supramolecular fibers of P and M handedness with thickness consistent in the dimensions of individual C3 molecules are obtained. The increase of concentrations induces these fibers to wrap together to form supramolecular fibrous bundles. Topochemical polymerization of the DA moieties can transform these supramolecular fibers into stable covalent polymers. We therefore believe that self-assembly of these C3-symmetric molecules with extended conjugated DA cores provides new prospects for the construction of supramolecular helical fibers through enhanced π-π stacking and creates a convenient strategy to furnish covalent chiral polymers of hierarchical structures through supramolecular assembly.

Design and Synthesis of α-Anomeric Diacetylene-Containing Glycosides as Photopolymerizable Molecular Gelators

Glycolipids with diacetylene functional groups are fascinating compounds with many practical uses. Among these, diacetylene-containing gelators are especially important because they can form photopolymerizable gels, which are useful stimuli-responsive materials. Inspired by the unique properties of diacetylene-containing gelators and to understand the structural influences especially the location of the diacetylene functional groups on the self-assembling properties, a series of 15 novel N-acetyl-d-glucosamine derivatives with the diacetylene functional group introduced at the anomeric position were designed and synthesized. The diacetylene function is attached to the sugar through α-glycosylation with the distance from the anomeric oxygen being varied from one, two, and three methylene groups, and the other side contains hydroxyl, carboxyl, phenyl, and alkyl substituents. Remarkably, all compounds can form self-assembled gels in one or more selected solvents. A majority of these synthesized diacetylene glycosides are effective gelators for ethanol/water (v/v 1:1), dimethyl sulfoxide/water (v/v 1:1), and toluene, and one compound also formed a hydrogel at 1.0 wt %. Typically, these glycosides form gels that are photopolymerizable to afford red-colored gels. Scanning electronic microscopy indicated that the gelators formed helices, fibers, and planar sheet-like morphologies. The chemical structures of the derivatives affected their gelation properties and responses to UV treatment. The carboxylic acid-functionalized derivative 17 was able to immobilize basic solutions and form transparent gels. We expect that these diacetylene glycosides especially the hydroxyl and carboxylic acid derivatives will be useful as stimuli-responsive glycolipids for biomedical research.

In Situ Supramolecular Gel Formed by Cyclohexane Diamine with Aldehyde Derivative

Low-molecular-weight gels have great potential for use in a variety of fields, including petrochemicals, healthcare, and tissue engineering. These supramolecular gels are frequently metastable, implying that their properties are kinetically controlled to some extent. Here, we report on the in situ supramolecular gel formation by mixing 1,3-cyclohexane diamine (1) and isocyanate derivative (2) without any catalysis at room temperature in various organic solvents. A mixture of building blocks 1 and 2 in various organic solvents, dichloromethane, tetrahydrofuran, chloroform, toluene, and 1,4-dioxane, resulted in the stable formation of supramolecular gel at room temperature within 60-100 s. This gel formation was caused by the generation of urea moieties, which allows for the formation of intermolecular hydrogen-bonding interactions via reactions 1 and 2. In situ supramolecular gels demonstrated a typical entangled fiber structure with a width of 600 nm and a length of several hundred μm. In addition, the supramolecular gels were thermally reversible by heating and cooling. The viscoelastic properties of supramolecular gels in strain and frequency sweets were enhanced by increasing the concentration of a mixed 1 and 2. Furthermore, the supramolecular gels displayed a thixotropic effect, indicating a thermally reversible gel.

Dendronized polydiacetylenes via photo-polymerization of supramolecular assemblies showing thermally tunable chirality

Transformation of supramolecular chiral assemblies into covalent polymers integrates characteristics of supramolecular chemistry together with covalent entities, leading to fabrication of covalent chiral materials through versatile supramolecular chiral assemblies. Here, we report supramolecular assembly of an amphiphilic dendronized 10,12-pentacosadiynoic amide (PCDA) in aqueous solutions to form twisted ribbons, which were transferred into covalent dendronized polydiacetylenes (PDAs) via photopolymerization. These supramolecular dendronized PCDA and the corresponding covalent dendronized PDAs showed unprecedent thermoresponsive properties. The thermally-induced dehydration and aggregations tuned reversibly their chiralities, which can be visually inspected through colour changes.

Circularly Polarized Photodetectors Based on Chiral Materials: A Review

Circularly polarized light (CPL) plays an important role in many photonic techniques, including tomographic scanning based on circular polarization ellipsometry, optical communication and information of spin, and quantum-based optical calculation and information processing. To fully exploit the functions of CPL in these fields, integrated photoelectric sensors capable of detecting CPL are essential. Photodetectors based on chiral materials can directly detect CPL due to their intrinsic optical activity, without the need to be coupled with polarizers and quarter-wave plates as in conventional photodetectors. This review summarizes the recent research progress in CPL photodetectors based on chiral materials. We first briefly introduce the CPL photodetectors based on different types of chiral materials and their working principles. Finally, current challenges and future opportunities in the development of CPL photodetectors are prospected.

Rational Design of Diphenyldiacetylene-Based Fluorescent Materials Enabling a 365-nm Light-Initiated Topochemical Polymerization

Photopolymerization of diacetylenes usually requires stringent reaction conditions like high energy irradiation of 254-nm light or even γ-rays, which are generally harmful to the human body and thus mild conditions with lower energy irradiation are required. In this study, different diphenyldiacetylene (DPDA) derivatives were rationally designed followed by the investigation of their photopolymerization behavior. It was found that the para-substituted amino groups could render the absorption band of DPDA bathochromically shifted, ensuring a 365-nm light wavelength coverage. On this basis, an organogel system was constructed by chemically modifying cholesteryl and lipoic acid onto the DPDA moiety in aromatic solvents. Such uniform self-assemblies further facilitated to a rather high degree of polymerization by 365-nm irradiation. As a kind of fluorescent materials, the whole polymerization process of this system can be visualized by a photoluminescent signal.

Structures and strategies for enhanced sensitivity of polydiacetylene(PDA) based biosensor platforms

Polydiacetylene (PDA) is a versatile polymer that has been studied in numerous fields because of its unique optical properties derived from alternating multiple bonds in the polymer backbone. The conjugated structure in the polymer backbone enables PDA to possess the ability of blue-red colorimetric transition when π-π interactions in the PDA backbone chain are disturbed by the external environment. The chromatic property of PDA disturbed by external stimuli can also emit fluorescence in the red region. Owing to the unique characteristics of PDA, it has been widely studied in facile and label-free sensing applications based on colorimetric or fluorescence signals for several decades. Among the various PDA structures, membrane structures assembled by amphiphilic molecules are widely used as a versatile platform because facile modification of the synthetic membrane provides extensive applications, such as receptor-ligand interactions, resulting in potent biosensors. To use PDA as a sensory material, several methods have been studied to endow the specificity to PDA molecules and to amplify the signal from PDA supramolecules. This is because selective and sensitive detection of target materials is required at an appropriate level corresponding to each material for applicable sensor applications. This review focuses on factors that affect the sensitivity of PDA composites and several strategies to enhance the sensitivity of the PDA sensor to various structures. Owing to these strategies, the PDA sensor system has achieved a higher level of sensitivity and selectivity, enabling it to detect multiple target materials for a full field of application.

Photoluminescence-enhanced cholesteric films: Coassembling copper nanoclusters with cellulose nanocrystals

Iridescent and luminescent composite films were fabricated through a coassembly strategy, in which glutathione-stabilized copper nanoclusters (GSH-CuNCs) were incorporated into chiral nematic structures of a cellulose nanocrystal (CNC) film. Through variations in the helical pitch, these composite films exhibited broadband reflection. The fluorescence emission spectrum of the composite film exhibited peaks at 439 and 600 nm, corresponding to crystallization-induced emission from CNCs and assembly-induced emission from CuNCs. The enhanced luminescence and prolonged lifetime of the composite film were attributed to the confinement effect of solid layers and attendant intermolecular interactions. By tuning the reaction time, temperature, and pH of the solution, the emission color and intensity of the CuNCs could be changed. At appropriate GSH and Cu²⁺ concentrations, the chiral organization of GSH-CuNCs enabled the composite CNC film to exhibit right-handed chiral fluorescence with an asymmetry factor of -0.16. Luminescent composite films were employed to fabricate LEDs with custom colors and patterns.

Dual Stimuli-Responsive High-Efficiency Circularly Polarized Luminescence from Light-Emitting Chiral Nematic Liquid Crystals

Considerable luminescence dissymmetry factor (g_lum) is vital for application implementation of circularly polarized luminescence (CPL) materials. Moreover, a dual CPL switch has promising prospects in high-security encryption and sensor devices. Herein, we designed and synthesized an emissive chiral nematic liquid crystal (N*-LC) by doping a luminescent chiral additive (NO₂-CS-C₆-Chol) into a nematic liquid crystal (5CB). The helical assembly structure produced by inducing the formation of N*-LC endows the prepared emissive N*-LC with a larger g_lum value. With the increase of the doping concentration from 1 to 10 wt %, the helical pitch (P) of N*-LC gradually decreases from 25.48 to 3.92 μm. The corresponding g_lum value increases first, reaches the maximum value (-0.38) at 6 wt %, and then decreases slightly. Further, the prepared emissive N*-LC doped with 6 wt % NO₂-CS-C₆-Chol is injected into an indium-tin oxide (ITO)-coated LC cell, to which a direct current (DC) electric field is applied. The g_lum value can be repeatedly shuttled between the "on" and "off" state by adjusting the applied voltage. Meanwhile, owing to the inherent thermal dependence of the liquid crystal phase structure, the g_lum value can also be switched between the on and off state by regulating the temperature. Therefore, an electrically controlled and thermocontrolled dual CPL switching device is successfully constructed.

Protonation-Triggered Supramolecular Gel from Macrocyclic Diacetylene: Gelation Behavior, Topochemical Polymerization, and Colorimetric Response

Supramolecular gels originating from the hierarchical self-assembly of low molecular weight organic molecules is a strongly emerging field of advanced material research for the fabrication of soft functional materials. Herein, a novel supramolecular gel was fabricated through the protonation-triggered unidirectional self-assembly of pyridine-attached macrocyclic diacetylene (PyMCDA). Basic nitrogen of a pyridine ring with a strong affinity toward proton transforms the neutral PyMCDA into gelator in its protonated pyridinium salt form (PyMCDA-H⁺), which further evolves to nano-fibrillar networks to yield a supramolecular gel. Under the irradiation of UV light, the white color gel turned to a robust covalently cross-linked blue-phase PDA gel. Interestingly, polymeric PyMCPDA-H⁺ gel exhibits a naked-eye detectable reversible blue-red colorimetric response for alternating acid/base (H₂SO₄/NH₄OH) and colorimetric sensitivity toward selected anions: CH₃COO^-, CN^-, HCOO^-, and CH₃CH₂COO^-. It is with the hope that this work point toward the utility and versatility of macrocyclic PDAs for constructing chromogenic supramolecular gels for their possible use in sensing systems.

Highly Sensitive Polydiacetylene Ensembles for Biosensing and Bioimaging

Polydiacetylenes are prepared from amphiphilic diacetylenes first through self-assembly and then polymerization. Different from common supramolecular assemblies, polydiacetylenes have stable structure and very special optical properties such as absorption, fluorescence, and Raman. The hydrophilic head of PDAs is easy to be chemically modified with functional groups for detection and imaging applications. PDAs will undergo a specific color change from blue to red, fluorescence enhancement and Raman spectrum changes in the presence of receptor ligands. These properties allow PDA-based sensors to have high sensitivity and specificity during analysis. Therefore, the PDAs have been widely used for detection of viruses, bacteria, proteins, antibiotics, hormones, sialic acid, metal ions and as probes for bioimaging in recent years. In this review, the preparation, polymerization, and detection mechanisms of PDAs are discussed, and some representative research advances in the field of bio-detection and bioimaging are highlighted.

Visualization and Quantification of Microwaves Using Thermoresponsive Color-Change Hydrogel

Visualization and quantification of invisible lights, such as microwaves, are significant for their safe use. In general, a sensitizer material combined with a transistor is used as electronic devices for the measurement. Here, we developed a thermoresponsive color-change hydrogel of poly(N-isopropylacrylamide) (PNIPAAm) cross-linked by a layered organic composite based on polydiacetylene (PDA) for visualization and colorimetric quantification of microwaves. The layered PDA in the PNIPAAm hydrogel showed the temperature-dependent gradual color change with heating. Irradiation of microwaves induced the color change of PDA through heating of water in the hydrogel and subsequent volume shrinkage. The color of the gel was applied to visualize the temperature distribution with increasing irradiation time of microwaves. Moreover, the power of the irradiated microwave was quantified by time to the complete color change of the gel. The results indicate that the stimulus conversion process has potentials for development of a variety of imaging and quantification devices based on the layered PDA.

Chirality Transfer in Coassembled Organogels Enabling Wide-Range Naked-Eye Enantiodifferentiation

Enantiodifferentiation is crucial in organic chemistry, pharmacochemistry, material chemistry, and life science. However, it remains tremendously challenging to achieve a broad enantioselectivity to different types of chiral substrates via a single-material design. Here, we report a coassembled organogel strategy with chirality transfer to make an enantioselective generality possible. This coassembly contains two components: a chiral rigid molecular linker and an achiral block copolymer. Different from routine helically packed chiral self-assemblies, chirality transfer from the linker to the copolymer directed the coassembly to form a phase-segregated twisted nanofiber, in cooperation with H-bonding and microphase segregation. An organogel was accordingly formed by the further cross-linking in ethanol, where the rigid chiral linker served as the scaffold. On this basis, the system becomes highly sensitive, enabling a naked-eye sensing toward the single enantiomer of a diverse series of chiral species (including axial, point, planar, and polymeric chirality) via gel-to-micelle transformation, due to the asymmetric interaction hampering the chirality transfer in the coassembly and destroying the hierarchical structure. Such a strategy, based on a significant amplification of the stereoselective interactions, facilitates a simple and straightforward way to distinguish a broad optical activity independent of devices.

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.

Tunable Upconverted Circularly Polarized Luminescence in Cellulose Nanocrystal Based Chiral Photonic Films

Integrating chromophores into chiral photonic crystals to fabricate materials that exhibit circularly polarized luminescence (CPL) is promising as this method allows efficient manipulation of the spontaneous emission within photonic bandgaps (PBGs). However, tuning the wavelength of CPL and the dissymmetry factor ( g_lum) in a convenient and accurate manner remains a significant challenge. Here, right-handed, tunable upconverted CPL (UC-CPL) emission was achieved by integrating multiple emissive, upconverting nanoparticles into cellulose nanocrystal based chiral photonic films that had tunable PBGs. Glycerol was used to tune the PBGs of the chiral photonic films, which yielded tunable UC-CPL emission at 450 and 620 nm with a tailored g_lum. Moreover, humidity responsive UC-CPL at blue wavelength was obtained from glycerol-composite photonic film, with a g_lum that ranged from -0.156 to -0.033. It was possible because the PBG and chirality of photonic composite was responded to the relative humidity. This work gives valuable insight into tunable and stimuli-responsive CPL photonic systems.

Multifunctional supramolecular self-assembly system for colorimetric detection of Hg2+, Fe3+, Cu2+ and continuous sensing of volatile acids and organic amine gases

A novel multifunctional gelator (1) based on an azobenzene derivative was designed and characterized. This compound could gelate some solvents including hexane, petroleum ether, DMSO, acetonitrile and ethanol through a heating-cooling procedure. The self-assembly process in different solvents was studied by means of UV-vis absorption and Fourier transform infrared (FTIR) spectra, field emission scanning electron microscopy (FESEM), rheological measurements, X-ray powder diffraction and water contact angle experiments. Interestingly, compound 1 had a high-contrast colorimetric detection ability towards Hg2+, Cu2+, Fe3+ and volatile acids and further organic amine gases in solution through its color change. At the same time, organogel 1 in acetonitrile also exhibited detection performance through a color or gel state change. In the response process, the self-assembly structures were changed from a nanofiber into a microsphere under induction by analytes. More significantly, film 1 could continuously detect volatile acids and organic amine gases. The number of cycles of film 1 for the detection of volatile acids and organic amine gases was at least seven times. The limit of detection (LOD) of film 1 towards TFA was calculated to be 0.0848 ppb. The sensing mechanisms were studied using 1HNMR, FESEM, UV-vis absorption spectra and HRMS. The intramolecular cyclization occurred on molecule 1 and a H2S molecule was lost during the detection process of Hg2+. It was proposed that the -N[double bond, length as m-dash]N- bonding could be coordinated by Fe3+ and Cu2+ and this further induced the absorption spectra and color change. For a volatile acid, it was possible that the volatile acid was combined with the N,N-dimethyl amine group of molecule 1. This research opens up a novel pathway to the fabrication of supramolecular self-assembly gels to detect polymetallic ions and trace volatile acids in the environment.

Multi-stimuli-responsiveness of a novel polydiacetylene-based supramolecular gel

Herein, a novel supramolecular gel was fabricated through the bi-component co-assembly strategy of commercially available 10,12-pentacosadiynoic acid (PCDA) and laboratory-synthesized amphiphilic co-gelator N-(2-(1H-imidazol-4-yl)ethyl)stearamide (IMSA), which contains one imidazole head group and a long alkyl chain tail, by synergetic noncovalent interactions. Upon irradiation of normal 254 nm UV light, blue polydiacetylene (PDA) could be obtained by topo-polymerization of the PCDA monomers in the gel phase. This PDA-based supramolecular gel is able to respond to various environmental stimuli and shows a blue-to-red chromatic transition, which could be observed by the naked eye. Specifically, upon exposure to heat, pH, metal cation and organic solvent stimuli, the PDA gel displays thermochromism, halochromism, ionochromism and solvatochromism, respectively. More interestingly, the differences of the above-mentioned stimuli-induced color transition of the blue PDA supramolecular gels could be characterized by UV-Vis absorption spectra and Raman spectra, therefore illuminating a bright application prospect in the area of chemosensing.

Co-assemblies of polydiacetylenes and metal ions for solvent sensing

We demonstrate an easy and low-cost approach for the colorimetric differentiation of organic solvents using co-assemblies of polydiacetylenes (PDAs) and metal ions. The co-assemblies were prepared by the self-assembly of amphiphilic 10,12-tricosa diynoic acid with different metal ions (Zn²⁺, Cu²⁺, Ni²⁺, Ca²⁺) and subsequent photopolymerization. Different metal ions underwent different interactions with the carboxyl groups on the side chains of poly(10,12-tricosa diynoic acid), which influenced the stimuli-responsiveness of the PDA/metal ion co-assemblies. As a result, the PDA/metal ion co-assemblies with different metal ions showed different solvatochromism. Based on this property, the co-assemblies were used as sensors to differentiate organic solvents.

Circularly Polarized Luminescence from a Pyrene-Cyclodextrin Supra-Dendron

Soft nanomaterials with circularly polarized luminescence (CPL) have been currently attracting great interest. Here, we report a pyrene-containing π-peptide dendron hydrogel, which shows 1D and 2D nanostructures with varied CPL activities. It was found that the individual dendrons formed hydrogels in a wide pH range (3-12) and self-assembled into helices with pH-tuned pitches. Through chirality transfer, the pyrene unit could show CPL originated from both the monomer and excimer bands. When cyclodextrin was introduced, different supra-dendrons were obtained with β-cyclodextrin (PGAc@β-CD) and γ-cyclodextrin (PGAc@γ-CD) through host-guest interactions, respectively. Interestingly, the PGAc@β-CD and PGAc@γ-CD supra-dendrons self-assembled into 2D nanosheet and entangled nanofibers, respectively, showing cyclodextrin induced circularly polarized emission from both the monomer and excimer bands of the pyrene moiety. Thus, through a simple host-guest interaction, both the nanostructures and the chiroptical activities could be modulated.

Chiral Nanoparticles with Full-Color and White CPL Properties Based on Optically Stable Helical Aromatic Imide Enantiomers

Chiral self-assembled organic nanoparticles with circularly polarized luminescence (CPL) properties can be utilized as a new kind of chiral luminescent materials for practical applications. However, no such chiral organic nanoparticles with full-color and white CPL properties have been reported so far. Herein, five pairs of self-assembled chiral nanoparticles based on optically stable helical aromatic amide enantiomers were conveniently obtained. The chiral nanoparticles showed about 200 nm uniform sphere, high fluorescence quantum yields, and large Stokes shifts. Especially, the chiral nanoparticles exhibited both obvious mirror-image circular dichroism signals and full-color CPL properties with luminescence dissymmetry factors of about 10^-3, which were comparable to those of CPL-active quantum dots. Moreover, the chiral organic nanoparticles with white CPL could also be easily achieved using the three-primary-color enantiomers via intermolecular energy resonance transfer.

Smartphone-Based VOC Sensor Using Colorimetric Polydiacetylenes

Owing to a unique colorimetric (typically blue-to-red) feature upon environmental stimulation, polydiacetylenes (PDAs) have been actively employed in chemosensor systems. We developed a highly accurate and simple volatile organic compound (VOC) sensor system that can be operated using a conventional smartphone. The procedure begins with forming an array of four different PDAs on conventional paper using inkjet printing of four corresponding diacetylenes followed by photopolymerization. A database of color changes (i.e., red and hue values) is then constructed on the basis of different solvatochromic responses of the 4 PDAs to 11 organic solvents. Exposure of the PDA array to an unknown solvent promotes color changes, which are imaged using a smartphone camera and analyzed using the app. A comparison of the color changes to the database promoted by the 11 solvents enables the smartphone app to identify the unknown solvent with 100% accuracy. Additionally, it was demonstrated that the PDA array sensor was sufficiently sensitive to accurately detect the 11 VOC gases.

Recent progress in the stabilization of supramolecular assemblies with functional polydiacetylenes

This minireview covers the most recent examples of covalent rigidification of supramolecular self-assemblies through the photopolymerization of diacetylene moieties.

Supramolecular gelatons: towards the design of molecular gels

The concept of supramolecular gelatons for the design of gels was proposed and described.

Hierarchical Self-Assembly of a Porphyrin into Chiral Macroscopic Flowers with Superhydrophobic and Enantioselective Property

Supramolecular self-assembly provides an efficient way to fabricate simple units into various hierarchical nano/microstructures, which could mimic the bioself-assembly and develop functional materials. Since chiral molecules and chiral nanostructures are widely adopted by biological systems, an introduction of the chiral factor into the self-assembly process will provide better understanding of the biological systems. Here, using a chiral amphiphilic histidine to assist the self-assembly of a porphyrin with four carboxylic acids, we obtained hierarchical chiral nano- to microstructures. We have found that through the hydrogen bonds/electrostatic interactions between the porphyrin and histidine derivatives, the π-π stacking between the porphyrins, and hydrophobic interactions between the amphiphilic histidine, the two components could self-assemble into chiral nanohelices and microflowers. The supramolecular chirality of these structures was confirmed by scanning electron microscopy images as well as the circular dichroism spectra, which was found to follow the molecular chirality of the histidine derivative. More interestingly, the microflower structures formed a superhydrophobic and chiral surface, which exhibited macroscopic enantioselective recognition of some l- and d-amino acids via contact angle measurements.

Self-Assembled Polydiacetylene Vesicle and Helix with Chiral Interface for Visualized Enantioselective Recognition of Sulfinamide

An l-glutamic acid terminated amphiphilic diacetylene was designed and found to self-assemble into vesicles in water and supramolecular gel with helical structures in mixed methanol/water solvent. Both the vesicles and the helices underwent topochemical photopolymerization under UV irradiation and changed to a blue color. During the self-assembly and photopolymerization, the chirality of localized l-glutamic acid was successfully transferred to polydiacetylene (PDA), which resulted in obvious CD signals in the PDA blue phase. Interestingly, the CD signals for PDA vesicles and helices were opposite due to the different packing modes in the PDA skeleton. However, although these two assembly systems own opposite supramolecular chirality, both of them showed the same enantioselective recognition of sulfinamide enantiomers, in which the assemblies with S-enantiomer turned red while the other remained blue in the presence of the R-enantiomer. It is suggested that the chiral interface composed of l-glutamic acid played an important role in the enantioselective recognition. This work revealed the function of molecular and supramolecular chirality in the supramolecular self-assembly system.

Strong Blue Emissive Supramolecular Self-Assembly System Based on Naphthalimide Derivatives and Its Ability of Detection and Removal of 2,4,6-Trinitrophenol

Two simple and novel gelators (G-P with pyridine and G-B with benzene) with different C-4 substitution groups on naphthalimide derivatives have been designed and characterized. Two gelators could form organogels in some solvents or mixed solvents. The self-assembly processes of G-P in a mixed solvent of acetonitrile/H₂O (1/1, v/v) and G-B in acetonitrile were studied by means of electron microscopy and spectroscopy. The organogel of G-P in the mixed solvent of acetonitrile/H₂O (1/1, v/v) formed an intertwined fiber network, and its emission spectrum had an obvious blue shift compared with that of solution. By contrast, the organogel of G-B in acetonitrile formed a straight fiber, and its emission had an obvious red shift compared with that of solution. G-P and G-B were employed in detecting nitroaromatic compounds because of their electron-rich property. G-P is more sensitive and selective toward 2,4,6-trinitrophenol (TNP) compared with G-B. The sensing mechanisms were investigated by ¹H NMR spectroscopic experiments and theoretical calculations. From these experimental results, it is proposed that electron transfer occurs from the electron-rich G-P molecule to the electron-deficient TNP because of the possibility of complex formation between G-P and TNP. The G-P molecule could detect TNP in water, organic solvent media, as well as using test strips. It is worth mentioning that the organogel G-P can not only detect TNP but also remove TNP from the solution into the organogel system.

Self-assembled nanohelix from a bolaamphiphilic diacetylene via hydrogelation and selective responsiveness towards amino acids and nucleobases

A bolaamphiphile with diacteylene mesogen unit and l-glutamic acid as the terminal group was newly designed and its self-assembly was investigated. The compound formed hydrogels with water upon heating and cooling. The as-formed gel could be switched to a dispersion upon mechanical shaking. Both the gel and the water dispersion undergo polymerization upon UV irradiation. However, the gel turned to blue and then purple red color, while the dispersion turned red directly. Using AFM and SEM observations, it was found that nanohelix was formed in the as-prepared gel and polymerized blue gels, while nanobelt was formed from the water dispersion. The blue nanohelix was stable but showed selective response to certain amino acids and nucleobases. It was found that the blue gel underwent shrinkage when reacting with charged amino acids such as Glu, Asp, Lys, Arg and His. In the shrunk gel, the solution phase further turned pink in the case of His and Arg. In addition, the blue gel showed also shrinkage and color change when reacting with cytosine.

Strong circularly polarized luminescence induced from chiral supramolecular assembly of helical nanorods

Chiral supramolecular assemblies (BNS–BPP) can exhibit circularly polarized luminescence (CPL) via electrostatic and π–π stacking interactions.