A chemosensor-based chiral coassembly with switchable circularly polarized luminescence

Chirally Selective and Switchable Luminescence from Achiral Quantum Emitters on Suspended Twisted Stacking Metasurfaces

Dynamic control of circularly polarized photoluminescence has aroused great interest in quantum optics and nanophotonics. Chiral plasmonic metasurfaces enable the manipulation of the polarization state via plasmon-photon coupling. However, current plasmonic light-emitting metasurfaces for effective deterministic modulation of spin-dependent emission at near-infrared wavelengths are underexplored in terms of dissymmetry and tunability. Here, we demonstrate a microfluidic hybrid emitting system of a suspended twisted stacking metasurface coated with PbS quantum dots. The suspended metasurface is fabricated with a single step of electron beam exposure, exhibiting a strong optical chirality of 309° μm-1 with a thickness of less than λ/10 at key spectral locations. With significant chiral-selective interactions, enhanced photoluminescence is achieved with strong dissymmetry in circular polarization. The dissymmetry factor of the induced circularly polarized emission can reach 1.54. More importantly, altering the refractive index of the surrounding medium at the bottom surface of the metasurface can effectively manipulate the chiroptical responses of the hybrid system, hence leading to chirality-reversed emission. This active hybrid emitting system could be a resultful platform for chirality-switchable light emission from achiral quantum emitters, holding great potential for anticounterfeiting, biosensing, light sources, imaging, and displays.

Rapid room-temperature phosphorescence chiral recognition of natural amino acids

Chiral recognition of amino acids is very important in both chemical and life sciences. Although chiral recognition with luminescence has many advantages such as being inexpensive, it is usually slow and lacks generality as the recognition module relies on structural complementarity. Here, we show that one single molecular-solid sensor, L-phenylalanine derived benzamide, can manifest the structural difference between the natural, left-handed amino acid and its right-handed counterpart via the difference of room-temperature phosphorescence (RTP) irrespective of the specific chemical structure. To realize rapid and reliable sensing, the doped samples are obtained as nanocrystals from evaporation of the tetrahydrofuran solutions, which allows for efficient triplet-triplet energy transfer to the chiral analytes generated in situ from chiral amino acids. The results show that L-analytes induce strong RTP, whereas the unnatural D-analytes produce barely any afterglow. The method expands the scope of luminescence chiral sensing by lessening the requirement for specific molecular structures.

Disassembly of spherical structures into nanohelices by good solvent dilution

Supramolecular self-assembly of low molecular weight molecules into various organic nanostructures has attracted considerable research interest. However, preparing organic nanostructures through a top-down method, such as the disassembly of one large structure into many smaller nanoscale nanostructures, still remains a big challenge. Here, we make use of anti-solvent method to regulate the hierarchical self-assembly of an achiral C3-symmetric molecule in THF/water to prepare various nanostructures, including spherical structures, nanofibers, nanoribbons and nanotwists. Interestingly, the spherical structures could disassemble into nanohelices through good solvent dilution, providing a nanoscale top-down method to prepare organic nanostructures.

Full-Color Circularly Polarized Luminescence of Supramolecular Polymers with Handedness Inversion Regulated by Anion and Temperature

Constructing full-color circularly polarized luminescence (CPL) materials with switchable handedness in the solid state is an appealing yet considerably challenging task, especially for supramolecular polymer films assembled from homochiral monomers. Herein, supramolecular polymers with full-color CPL and inverted handedness are realized through the coassembly of a homochiral cholesterol derivative (PVPCC), metal ions (Zn2+), and achiral fluorescent dyes. The obtained coassembled systems show anion-directed supramolecular chirality inversion by exchanging the anions of NO3-, ClO4-, BF4-, and Cl-. For instance, the negative CD and right-handed CPL are detected in the PVPCC/Zn(NO3)2 aggregates, which convert into positive CD and left-handed CPL after introducing Cl-, corresponding to the transformation from nanorods to nanofibers. Furthermore, the tunable CPL color and handedness inversion of the coassembly system of PVPCC/Zn(NO3)2 and achiral fluorescent dyes can be established by alternately changing the assembling temperature of 298 and 273 K. Importantly, the full-color CPL polymeric materials are then constructed by doping the PVPCC/Zn(NO3)2/dyes complexes into poly(methyl methacrylate) (PMMA) film, which maintains the handedness inversion and shows the enhanced CPL performance. The work not only deepens the understanding of chirality inversion in supramolecular chemistry but also helps to construct full-color CPL materials with switchable handedness from homochiral building blocks in materials science.

Chiral Carbon Dots and Chiral Carbon Dots with Circularly Polarized Luminescence: Synthesis, Mechanistic Investigation and Applications

Chiral carbon dots (CCDs) can be widely used in various fields such as chiral recognition, chiral catalysis and biomedicine because of their unique optical properties, low toxicity and good biocompatibility. In addition, CCDs with circularly polarized luminescence (CPL) can be synthesized, thus broadening the prospects of CCDs applications. Since the research on CCDs is still in its infancy, this paper reviews the chiral origin, formation mechanism, chiral evolution, synthesis and emerging applications of CCDs, with a special focus on CCDs with CPL activity. It is hoped that it will provide some reference to solve the current problems faced by CCDs. Finally, the opportunities and challenges of the current research on CCDs are described, and their future development trends have also been prospected.

Chiral Polymer Dots Show Unexpected Versatility of Highly Ordered Self-Assembly into Chiroptical Liquid Crystals, Ultra-Thin Films, and Long-Ribbons

Compared to the organic counterparts, chiral self-assembly of nanomaterials shows persistency to kinetic factors such as solvent environments, and consequently, dynamic modulation of self-assembly and functions remains major challenge. Here, it is shown that alkylated, chiral polymer dots (c-PDs) give highly ordered self-assemblies with amplified chirality adaptive to solvent environments, and one-to-many hierarchical aggregation can be realized. The c-PDs tended to self-assemble into nanohelices with cubic packing in the solid state, which, thanks to the thermo-responsiveness, transformed into thermic liquid crystals upon heating. Cotton effects and circularly polarized luminescence evidenced the chirality transfer from central chirality to supramolecular chirality. At the air-water interface, the c-PDs are self-assembled into monolayers, which further stack into multiple layers with chirality transfer and highly ordered packing. In addition, undergoing a good/poor solvent exchange, the c-PDs afforded ultra-long microribbons up to a length scale of millimeters, which are constituted by the bilayer lamellar stacking. The versatile chiral self-assembly modalities with long-range ordered packing arrays of carbonized c-PDs via solvent strategy are realized. This feature is comparable to the organic species, although the c-PDs have no atomic precise structures. This work would surely expand the applications of quantum dot ordered self-assembly with adaptiveness to kinetic factors.

Chiroptical Synaptic Heterojunction Phototransistors Based on Self-Assembled Nanohelix of π-Conjugated Molecules for Direct Noise-Reduced Detection of Circularly Polarized Light

High-performance chiroptical synaptic phototransistors are successfully demonstrated using heterojunctions composed of a self-assembled nanohelix of a π-conjugated molecule and a metal oxide semiconductor. To impart strong chiroptical activity to the device, a diketopyrrolopyrrole-based π-conjugated molecule decorated with chiral glutamic acid is newly synthesized; this molecule is capable of supramolecular self-assembly through noncovalent intermolecular interactions. In particular, nanohelix formed by intertwinded fibers with strong and stable chiroptical activity in a solid-film state are obtained through hydrogen-bonding-driven, gelation-assisted self-assembly. Phototransistors based on interfacial charge transfer at the heterojunction from the chiroptical nanohelix to the metal oxide semiconductor show excellent chiroptical detection with a high photocurrent dissymmetry factor of 1.97 and a high photoresponsivity of 218 A W-1 . The chiroptical phototransistor demonstrates photonic synapse-like, time-dependent photocurrent generation, along with persistent photoconductivity, which is attributed to the interfacial charge trapping. Through the advantage of synaptic functionality, a trained convolutional neural network successfully recognizes noise-reduced circularly polarized images of handwritten alphabetic characters with better than 89.7% accuracy.

Probing Molecular Chirality on the Self-Assembly and Gelation of Naphthalimide-Conjugated Dipeptides

In this work, 1,8-naphthalimide (NMI)-conjugated three hybrid dipeptides constituted of a β-amino acid and an α-amino acid have been designed, synthesized, and purified. Here, in the design, the chirality of the α-amino acid was varied to study the effect of molecular chirality on the supramolecular assembly. Self-assembly and gelation of three NMI conjugates were studied in mixed solvent systems [water and dimethyl sulphoxide (DMSO)]. Interestingly, chiral NMI derivatives [NMI-βAla-^lVal-OMe (NLV) and NMI-βAla-^dVal-OMe (NDV)] formed self-supported gels, while the achiral NMI derivative [NMI-βAla-Aib-OMe, (NAA)] failed to form any kind of gel at 1 mM concentration and in a mixed solvent (70% water in DMSO medium). Self-assembly processes were thoroughly investigated using UV-vis spectroscopy, nuclear magnetic resonance (NMR), fluorescence, and circular dichroism (CD) spectroscopy. A J-type molecular assembly was observed in the mixed solvent system. The CD study indicated the formation of chiral assembled structures for NLV and NDV, which were mirror images of one another, and the self-assembled state by NAA was CD-silent. The nanoscale morphology of the three derivatives was studied using scanning electron microscopy (SEM). In the case of NLV and NDV, left- and right-handed fibrilar morphologies were observed, respectively. In contrast, a flake-like morphology was noticed for NAA. The DFT study indicated that the chirality of the α-amino acid influenced the orientation of π-π stacking interactions of naphthalimide units in the self-assembled structure that in turn regulated the helicity. This is a unique work where molecular chirality controls the nanoscale assembly as well as the macroscopic self-assembled state.

Self-assembled supramolecular artificial light-harvesting nanosystems: construction, modulation, and applications

Artificial light-harvesting systems, an elegant way to capture, transfer and utilize solar energy, have attracted great attention in recent years. As the primary step of natural photosynthesis, the principle of light-harvesting systems has been intensively investigated, which is further employed for artificial construction of such systems. Supramolecular self-assembly is one of the feasible methods for building artificial light-harvesting systems, which also offers an advantageous pathway for improving light-harvesting efficiency. Many artificial light-harvesting systems based on supramolecular self-assembly have been successfully constructed at the nanoscale with extremely high donor/acceptor ratios, energy transfer efficiency and the antenna effect, which manifests that self-assembled supramolecular nanosystems are indeed a viable way for constructing efficient light-harvesting systems. Non-covalent interactions of supramolecular self-assembly provide diverse approaches to improve the efficiency of artificial light-harvesting systems. In this review, we summarize the recent advances in artificial light-harvesting systems based on self-assembled supramolecular nanosystems. The construction, modulation, and applications of self-assembled supramolecular light-harvesting systems are presented, and the corresponding mechanisms, research prospects and challenges are also briefly highlighted and discussed.

Dual Band-Edge Enhancing Overall Performance of Upconverted Near-Infrared Circularly Polarized Luminescence for Anticounterfeiting

Circularly polarized luminescence (CPL) is one of the critical chiroptical properties for chiral nanomaterials, which exhibit wide potential applications in many research fields. However, it remains a big challenge for real application, limited by their small luminescence dissymmetry factor or low emission intensity. Here, an upconverted near-infrared circularly polarized luminescence (UC-NIR-CPL) system is constructed based on the chiroptical property of chiral liquid crystals, embedding with the lanthanide-doped upconversion nanoparticles. More importantly, a strategy for improving the overall performance of UC-NIR-CPL was proposed and realized by taking advantage of the "dual-band-edge enhancement effect", wherein the g_lum value was amplified, while the NIR emission intensity showed dual enhancement and the threshold of excitation was decreased. Based on the improved overall performance of the UC-NIR-CPL, which can be used as a distinctive covert light, a kind of photonic barcode with multiple encryptions was realized. These findings will upgrade the level of information encryption through improving the overall performance of CPL-active materials.

Photoprogrammable circularly polarized phosphorescence switching of chiral helical polyacetylene thin films

The developments of pure organic room-temperature phosphorescence (RTP) materials with circularly polarized luminescence (CPL) have significantly facilitated the future integration and systemization of luminescent material in fundamental science and technological applications. Here, a type of photoinduced circularly polarized RTP materials are constructed by homogeneously dispersing phosphorescent chiral helical substituted polyacetylenes into a processable poly(methyl methacrylate) (PMMA) matrix. These substituted polyacetylenes play vital roles in the propagation of CPL and present prominently optical characteristics with high absorption and luminescent dissymmetric factors up to 0.029 (g_abs) and 0.019 (g_lum). The oxygen consumption properties of the films under UV light irradiation endow materials with dynamic chiro-optical functionality, which can leverage of light to precisely control and manipulate the circularly polarized RTP properties with the remarkable advantages of being contactless, wireless and fatigue-resistant. Significantly, the distinct materials with dynamic properties can be used as anti-counterfeiting materials involving photoprogrammability.

Tunable Circularly Polarized Luminescence via Chirality Induction and Energy Transfer from Organic Films to Semiconductor Nanocrystals

Circularly polarized luminescent (CPL) films with high dissymmetry factors hold great potential for optoelectronic applications. Herein, we propose a strategy for achieving strongly dissymetric CPL in nanocomposite films based on chirality induction and energy transfer to semiconductor nanocrystals. First, focusing on a purely organic system, aggregation-induced emission (AIE) and CPL activity of organic liquid crystals (LCs) forming helical nanofilaments was detected, featuring green emission with high dissymmetry factors g_lum ∼ 10^-2. The handedness of helical filaments, and thus the sign of CPL, was controlled via minute amounts of a small chiral organic dopant. Second, nanocomposite films were fabricated by incorporating InP/ZnS semiconductor quantum dots (QDs) into the LC matrix, which induced the chiral assembly of QDs and endowed them with chiroptical properties. Due to the spectral matching of the components, energy transfer (ET) from LC to QDs was possible enabling a convenient way of tuning CPL wavelengths by varying the LC/QD ratio. As obtained, composite films exhibited absolute g_lum values up to ∼10^-2 and thermally on/off switchable luminescence. Overall, we demonstrate the induction of chiroptical properties by the assembly of nonchiral building QDs on the chiral organic template and energy transfer from organic films to QDs, representing a simple and versatile approach to tune the CPL activity of organic materials.

Two Ratiometric Fluorescent Probes Based on the Hydroxyl Coumarin Chalcone Unit with Large Fluorescent Peak Shift for the Detection of Hydrazine in Living Cells

Hydrazine is widely used in industrial and agricultural production, but excessive hydrazine possesses a serious threat to human health and environment. Here two new ratiometric fluorescence probes, DDP and DDC, with the hydroxyl coumarin chalcone unit as the sensing site are developed, which can achieve colorimetric and ratiometric recognition for hydrazine with good sensitivity, excellent selectivity, and anti-interference. The calculated fluorescence limits of detections are 0.26 μM (DDC) and 0.14 μM (DDP). The ratiometric fluorescence response to hydrazine is realized through the adjustment of donor and receptor units in coumarin conjugate structure terminals, accompanied by fluorescence peak shift about 200 nm (DDC, 188 nm; DDP, 229 nm). Stronger electropositivity in the carbon-carbon double bond is helpful to the first phase addition reaction between the probe and hydrazine. Higher phenol activity in the hydroxyl coumarin moiety will facilitate the following dihydro-pyrazole cyclization reaction. In addition, both of these probes realized the convenient detection of hydrazine vapor. The probes were also successfully applied to detect hydrazine in actual water samples, different soils, and living cells.

Amplified Circularly Polarized Electroluminescence Behavior Triggered by Helical Nanofibers from Chiral Co-assembly Polymers

Two chiral binaphthyl polymers (R/S-P1 and R/S-P2) with different dihedral angles of the binaphthyl moiety were chosen as chiral inducers to construct chiral co-assemblies with an achiral pyrene-naphthalimide dye (NPy) and then acted as the emitting layer (EML) of circularly polarized electroluminescence (CP-EL) devices. The anchored dihedral angle of R/S-P2 not only exhibited the enhanced chirality signal, but also had a strong chirality-inducing effect on the achiral NPy dye in the chiral co-assembly (R/S-P2)_0.6 -(NPy)_0.4 . After annealing at 120 °C, the CPL signal (|g_em |) of ordered helical nano-fibers (R/S-P2)_0.6 -(NPy)_0.4 was amplified to 5.6×10^-2 , which was about 6-fold larger than that of (R/S-P1)_0.6 -(NPy)_0.4 . The amplified g_em value of (R/S-P2)_0.6 -(NPy)_0.4 was due to the formation of a helical co-assembly through the strong π-π stacking interaction between the R/S-P2 and the achiral NPy. This kind of ordered helical nano-fibers (R/S-P2)_0.6 -(NPy)_0.4 acted as the EML of CP-OLEDs, and achieved an excellent CP-EL performance (|g_EL |=4.8×10^-2 ).

Eutectogels as Matrices to Manipulate Supramolecular Chirality and Circularly Polarized Luminescence

Solvent is regarded as a factor in tuning the supramolecular chirality of self-assemblies. Deep eutectic solvents (DESs) show diverse properties in contrast to other common solvents, which are emerging in fabricating functional aggregates and nanoarchitectures. Nevertheless, the emergence and manipulation of supramolecular chirality in DES still remain mysterious. Exploring supramolecular chirality in DES would produce tunable chiroptical materials considering their feasible preparation process and abundant hydrogen bonding sites. In this work, we explored the occurrence and manipulation of supramolecular chirality in DES. Transfer from inherent chiral DES to solutes in either aggregated or monomeric building units is blocked. However, the chiral assembly of π-conjugated amino acids was realized. Compared to aqueous media, self-assembly in DES hinders the spontaneous structural and chirality evolution that benefit from efficient solvation, where the π-conjugated amino acids were involved as hydrogen bonding donors. DES performs as a dye-friendly matrix to afford chiroptical eutectogels with tunable circularly polarized luminescence, whereby a large dissymmetry g-factor of up to 0.015 was realized. DES behaves as feasible and flexible solvents to fabricate and stabilize functional soft chiral self-assemblies with controllable chiroptical properties.

Double helical π-aggregate nanoarchitectonics for amplified circularly polarized luminescence

The canonical double helical π-stacked array of base pairs within DNA interior has inspired the interest in supramolecular double helical architectures with advanced electronic, magnetic and optical functions. Here, we report a selective-recognized and chirality-matched co-assembly strategy for the fabrication of fluorescent π-amino acids into double helical π-aggregates, which show exceptional strong circularly polarized luminescence (CPL). The single crystal structure of the optimal combination of co-assemblies shows that the double-stranded helical organization of these π-amino acids is cooperatively assisted by both CH-π and hydrogen-bond arrays with chirality match. The well-defined spatial arrangement of the π-chromophores could effectively suppress the non-radiative decay pathways and facilitate chiral exciton couplings, leading to superior CPL with a strong figure of merit (g_lum = 0.14 and QY = 0.76). Our findings might open a new door for developing DNA-inspired chiroptical materials with prominent properties by enantioselective co-assembly initiated double helical π-aggregation.

Synthesized or self-assembled helical architectures advance the development of chiral functional materials. Here the authors report a selective-recognized and chirality-matched co-assembly strategy for the fabrication of fluorescent π-amino acids into double helical π-aggregates with exceptional strong circularly polarized luminescence

Multiple Responsive CPL Switches in an Enantiomeric Pair of Perovskite Confined in Lanthanide MOFs

Circularly polarized luminescence (CPL) switches have attracted widespread attention due to their potential applications in advanced information technologies. However, the design and fabrication of solid-state multiple-responsive CPL switches remain challenging. Here, through self-assembly of chiral metal-organic frameworks (MOFs) and perovskite nanocrystals (NCs), a pair of crystalline enantiomeric (P)-(+)/(M)-(-)-EuMOF⊃MAPbX₃ (MA = CH₃ NH₃ ⁺ , X = Cl^- , Br^- , I^- ) adducts is prepared, where the achiral MAPbBr₃ perovskite NCs embedded into chiral MOFs inherit the chirality of host MOFs by host-guest EuBr and PbO coordination bonds, which is demonstrated by synchrotron-radiation-based X-ray absorption spectroscopy. The chiral adducts show enhanced photoluminescence quantum yield (PLQY), good thermal stability of CPL in air, and photoswitchable CPL properties upon altering different UV irradiation. Based on two chiral emission centers and their different characteristics, reversible CPL switches are realized upon a diversity of external stimuli, for example, chemicals (water /CH₃ NH₃ Br solution) or temperatures (room temperature/high temperature). Benefiting from the extraordinary stimuli-responsive and highly reversible switchable CPL, multiple information encryptions and decryptions integrated with CPL, together with a chiroptical logic gate are successfully designed. This work opens a new avenue to generally fabricate solid-state CPL composite materials and develops new applications based on switchable CPL.