Photon Upconverted Circularly Polarized Luminescence via Triplet–Triplet Annihilation

Circularly polarized luminescent materials are of increasing attention due to their potential applications in advanced optical technologies, such as chiroptical devices and optical sensing. Recently, in all reported circularly polarized luminescent materials, high‐energy excitation results in low‐energy or downconverted circularly polarized luminescence (CPL) emission. Although photon upconversion—i.e., the conversion of low‐energy light into higher‐energy emission, with a wide variety of applications—has been widely reported, the integration of photon upconversion and CPL in one chiral system to achieve higher‐energy CPL emission has never been reported. Herein, a brief review is provided of recent achievements in photon‐upconverted CPL via the triplet–triplet annihilation mechanism, focusing on the amplified dissymmetry factor g_lum through energy transfer process and dual upconverted and downconverted CPL emission through chirality and energy transfer process.     

Enantiomeric MOF Crystals Using Helical Channels as Palettes with Bright White Circularly Polarized Luminescence

The host–guest chemistry of metal–organic frameworks (MOFs) has enabled the derivation of numerous new functionalities. However, intrinsically chiral MOFs (CMOFs) with helical channels have not been used to realize crystalline circularly polarized luminescence (CPL) materials. Herein, enantiomeric pairs of MOF crystals are reported, where achiral fluorophores adhere to the inner surface of helical channels via biology-like H-bonds and hence inherit the helicity of the host MOFs, eventually amplifying the luminescence dissymmetry factor (g_lum) of the host l /d -CMOF (±1.50 × 10⁻³) to a maximum of ±0.0115 for the composite l /d -CMOF⊃fluorophores. l /d -CMOF⊃fluorophores in pairs generate bright color-tunable CPL and almost ideal white CPL (0.33, 0.32) with a record-high photoluminescence quantum yield of ≈30%, which are further assembled into a white circularly polarized light-emitting diode. The present strategy opens a new avenue for propagating the chirality of MOFs to realize universal chiroptical materials.     

Full‐Color Tunable Circularly Polarized Luminescent Nanoassemblies of Achiral AIEgens in Confined Chiral Nanotubes

Circularly polarized luminescent (CPL) materials are currently attracting great interest. While a chiral building is usually necessary in order to obtain CPL materials, here, this study proposes a general approach for fabricating 1D circularly polarized luminescent nanoassemblies from achiral aromatic molecules or aggregation‐induced emissive compounds (AIEgens). It is found that a C₃ symmetric chiral gelator can individually form hexagonal nanotube structures and encapsulate the guest molecules. When achiral AIEgens are encapsulated into the confined nanotubes via organogelation, the AIEgens will emit circularly polarized luminescence. Further, the direction of the CPL could be controlled by the supramolecular chirality of the nanotube. Remarkably, the approach is universal and various kinds of the AIEgens can be doped to show such property, providing a full‐color‐tunable circularly polarized luminescence.     

Endowing Perovskite Nanocrystals with Circularly Polarized Luminescence

Perovskite nanocrystals are attracting great interest due to their excellent photonic properties. Here, through a supramolecular self‐assembly approach, the perovskite nanocrystals (NCs) with a novel circularly polarized luminescence (CPL) are successfully endowed. It is found that the achiral perovskite NCs can coassemble with chiral gelator in nonpolar solvents, in which the gelator molecules modify the surface of the perovskite NCs. Through such cogelation, the molecular chirality can transfer to the NCs resulting in CPL signals with a dissymmetric factor (g_lum) up to 10^?3. Furthermore, depending on the molecular chirality of the gelator, the CPL sense can be selected and the mirror‐imaged CPL is obtained. Such gels can be further embedded into the polymer film to facilitate flexible CPL devices. It is envisaged that this approach will afford a new insight into the designing of the functional chiroptical materials.     

Tailoring MoS2 Valley‐Polarized Photoluminescence with Super Chiral Near‐Field

Transition metal dichalcogenides with intrinsic spin–valley degrees of freedom hold great potentials for applications in spintronic and valleytronic devices. MoS₂ monolayer possesses two inequivalent valleys in the Brillouin zone, with each valley coupling selectively with circularly polarized photons. The degree of valley polarization (DVP) is a parameter to characterize the purity of valley‐polarized photoluminescence (PL) of MoS₂ monolayer. Usually, the detected values of DVP in MoS₂ monolayer show achiral property under optical excitation of opposite helicities due to reciprocal phonon‐assisted intervalley scattering process. Here, it is reported that valley‐polarized PL of MoS₂ can be tailored through near‐field interaction with plasmonic chiral metasurface. The resonant field of the chiral metasurface couples with valley‐polarized excitons, and tailors the measured PL spectra in the far‐field, resulting in observation of chiral DVP of MoS₂‐metasurface under opposite helicities excitations. Valley‐contrast PL in the chiral heterostructure is also observed when illuminated by linearly polarized light. The manipulation of valley‐polarized PL in 2D materials using chiral metasurface represents a viable route toward valley‐polaritonic devices.     

One-Dimensional Chiral Copper Iodide Chain-Like Structure Cu4I4(R/S-3-quinuclidinol)3 with Near-Unity Photoluminescence Quantum Yield and Efficient Circularly Polarized Luminescence

Chiral organic−inorganic hybrid metal halide materials have shown great potential for circularly polarized luminescence (CPL) related applications for their tunable structures and efficient emissions. Here, this work combines the highly emissive Cu₄I₄ cubane cluster with chiral organic ligand R/S-3-quinuclidinol, to construct a new type of 1D Cu-I chains, namely Cu₄I₄(R/S-3-quinuclidinol)₃, crystallizing in noncentrosymmetric monoclinic P2₁ space group. These enantiomorphic hybrids exhibit long-term stability and show bright yellow emission with a photoluminescence quantum yield (PLQY) close to 100%. Due to the successful chirality transfer from the chiral ligands to the inorganic backbone, the enantiomers show intriguing chiroptical properties, such as circular dichroism (CD) and CPL. The CPL dissymmetry factor (g_lum) is measured to be ≈4 × 10⁻³. Time-resolved photoluminescence (PL) measurements show long averaged decay lifetime up to 10 µs. The structural details within the Cu₄I₄ reveal the chiral nature of these basic building units, which are significantly different than in the achiral case. This discovery provides new structural insights for the design of high performance CPL materials and their applications in light emitting devices.     

Helically assembled π-conjugated polymers with circularly polarized luminescence

We review the recent progress in the field of helically assembled π-conjugated polymers, focusing on aromatic conjugated polymers with interchain helical π-stacking that exhibit circularly polarized luminescence (CPL). In Part 1, we discuss optically active polymers with white-colored CPL and the amplification of the circular polarization through liquid crystallinity. In Part 2, we focus on the stimuli-responsive CPL that results from changes in the conformation and aggregation state of π-conjugated molecules and polymers. In Part 3, we discuss the self-assembly of achiral cationic π-conjugated polymers into circularly polarized luminescent supramolecular nanostructures with the aid of other chiral molecules.     

Low Detection Limit Circularly Polarized Light Detection Realized by Constructing Chiral Perovskite/Si Heterostructures

Chiral perovskites have been demonstrated as promising candidates for direct circularly polarized light (CPL) detection due to their intrinsic chirality and excellent charge transport ability. However, chiral perovskite-based CPL detectors with both high distinguishability of left- and right-handed optical signals and low detection limit remain unexplored. Here, a heterostructure, (R-MPA)₂MAPb₂I₇/Si (MPA = methylphenethylamine, MA = methylammonium) is constructed, to achieve high-sensitive and low-limit CPL detection. The heterostructures with high crystalline quality and sharp interface exhibit a strong built-in electric field and a suppressed dark current, not only improving the separation and transport of the photogenerated carriers but also laying a foundation for weak CPL signals detection. Consequently, the heterostructure-based CPL detector obtains a high anisotropy factor up to 0.34 with a remarkably low CPL detection limit of 890 nW cm⁻² under the self-driven mode. As a pioneering study, this work paves the way for designing high-sensitive CPL detectors that simultaneously have great distinguishing capability and low detection limit of CPL.     

Chiral Octahydro‐Binaphthol Compound‐Based Thermally Activated Delayed Fluorescence Materials for Circularly Polarized Electroluminescence with Superior EQE of 32.6% and Extremely Low Efficiency Roll‐Off

Circularly polarized organic light‐emitting diodes (CP‐OLEDs) are particularly favorable for the direct generation of CP light, and they demonstrate a promising application in 3D display. However, up to now, such CP devices have suffered from low brightness, insufficient efficiency, and serious efficiency roll‐off. In this study, a pair of octahydro‐binaphthol ( OBN )‐based chiral emitting enantiomers, (R/S)‐OBN‐Cz , are developed by ingeniously merging a chiral source and a luminophore skeleton. These chirality–acceptor–donor (C–A–D)‐type and rod‐like compounds concurrently generate thermally activated delayed fluorescence with a small ΔE_ST of 0.037 eV, as well as a high photoluminescence quantum yield of 92% and intense circularly polarized photoluminescence with dissymmetry factors (|g_PL|) of ≈2.0 × 10^?3 in thin films. The CP‐OLEDs based on (R/S)‐OBN‐Cz enantiomers not only display obvious circularly polarized electroluminescence signals with a |g_EL| of ≈2.0 × 10^?3, but also exhibit superior efficiencies with maximum external quantum efficiency (EQE_max) up to 32.6% and extremely low efficiency roll‐off with an EQE of 30.6% at 5000 cd m^?2, which are the best performances among the reported CP devices to date.     

Preparation of chiral poly(diacetylene) films from 10,12-pentacosadiynoic acid using circularly polarized light

By irradiating evaporated 10,12-pentacosadiynoic acid (p-DA) monomer film with circularly polarized light (CPL), we prepared chiral poly(diacetylene) [PDA] film. The circular dichroism (CD) was obtained reproducibly, depending on the rotational direction of the CPL. The induced chirality showed the dependence on the substrate temperature used for the preparation of evaporated p-DA monomer films, and it was stable after the transition to red-phase by annealing. Results suggest that side chain of polymer made a significant contribution to the formation of red-phase chiral PDA.     

Fullerene Desymmetrization as a Means to Achieve Single‐Enantiomer Electron Acceptors with Maximized Chiroptical Responsiveness

Solubilized fullerene derivatives have revolutionized the development of organic photovoltaic devices, acting as excellent electron acceptors. The addition of solubilizing addends to the fullerene cage results in a large number of isomers, which are generally employed as isomeric mixtures. Moreover, a significant number of these isomers are chiral, which further adds to the isomeric complexity. The opportunities presented by single‐isomer, and particularly single‐enantiomer, fullerenes in organic electronic materials and devices are poorly understood however. Here, ten pairs of enantiomers are separated from the 19 structural isomers of bis[60]phenyl‐C61‐butyric acid methyl ester, using them to elucidate important chiroptical relationships and demonstrating their application to a circularly polarized light (CPL)‐detecting device. Larger chiroptical responses are found, occurring through the inherent chirality of the fullerene. When used in a single‐enantiomer organic field‐effect transistor, the potential to discriminate CPL with a fast light response time and with a very high photocurrent dissymmetry factor (g_ph = 1.27 ± 0.06) is demonstrated. This study thus provides key strategies to design fullerenes with large chiroptical responses for use as chiral components of organic electronic devices. It is anticipated that this data will position chiral fullerenes as an exciting material class for the growing field of chiral electronic technologies.     

In Situ Investigation on the Protein Corona Formation of Quantum Dots by Using Fluorescence Resonance Energy Transfer

A fundamental understanding of nanoparticle–protein corona and its interactions with biological systems is essential for future application of engineered nanomaterials. In this work, fluorescence resonance energy transfer (FRET) is employed for studying the protein adsorption behavior of nanoparticles. The adsorption of human serum albumin (HSA) onto the surface of InP@ZnS quantum dots (QDs) with different chirality (d ‐ and l ‐penicillamine) shows strong discernible differences in the binding behaviors including affinity and adsorption orientation that are obtained upon quantitative analysis of FRET data. Circular dichroism spectroscopy further confirms the differences in the conformational changes of HSA upon interaction with d ‐ and l ‐chiral QD surfaces. Consequently, the formed protein corona on chiral surfaces may affect their following biological interactions, such as possible protein exchange with serum proteins plasma as well as cellular interactions. These results vividly illustrate the potential of the FRET method as a simple yet versatile platform for quantitatively investigating biological interactions of nanoparticles.     

Circularly Polarized Luminescence in Nanoassemblies: Generation,Amplification, and Application

Currently, the development of circularly polarized luminescent (CPL) materials has drawn extensive attention due to the numerous potential applications in optical data storage, displays, backlights in 3D displays, and so on. While the fabrication of CPL-active materials generally requires chiral luminescent molecules, the introduction of the “self-assembly” concept offers a new perspective in obtaining the CPL-active materials. Following this approach, various self-assembled materials, including organic-, inorganic-, and hybrid systems can be endowed with CPL properties. Benefiting from the advantages of self-assembly, not only chiral molecules, but also achiral species, as well as inorganic nanoparticles have potential to be self-assembled into chiral nanoassemblies showing CPL activity. In addition, the dissymmetry factor, an important parameter of CPL materials, can be enhanced through various pathways of self-assembly. Here, the present status and progress of self-assembled nanomaterials with CPL activity are reviewed. An overview of the key factors in regulating chiral emission materials at the supramolecular level will largely boost their application in multidisciplinary fields.     

Modular Molecular Self‐Assembly for Diversified Chiroptical Systems

Bottom‐up multicomponent molecular self‐assembly is an efficient approach to fabricate and manipulate chiral nanostructures and their chiroptical activities such as the Cotton effect and circular polarized luminescence (CPL). However, the integrated coassembly suffers from spontaneous and inherent systematic pathway complexity with low yield and poor fidelity. Consequently, a rational design of chiral self‐assembled systems with more than two components remains a significant challenge. Herein, a modularized, ternary molecular self‐assembly strategy that generates chiroptically active materials at diverse hierarchical levels is reported. N‐terminated aromatic amino acids appended with binding sites for charge transfer and multiple hydrogen bonds undergo the evolution of supramolecular chirality with unique handedness and luminescent color, generating abundant CPL emission with high luminescence dissymmetry factor values in precisely controlled modalities. Ternary coassembly facilitates high‐water‐content hydrogel formation constituted by super‐helical nanostructures, demonstrating a helix to toroid topological transition. This discovery would shed light on developing complicated multicomponent systems in mimicking biological coassembly events.     

A Singlet Oxygen Generating Agent by Chirality‐dependent Plasmonic Shell‐Satellite Nanoassembly

Photodynamic therapy (PDT) agent, which generates singlet oxygen (¹O₂) under light, has attracted significant attention for its broad biological and medical applications. Here, DNA‐driven shell–satellite (SS) gold assemblies as chiral photosensitizers are first fabricated. The chiral plasmonic nanostructure, coupling with cysteine enantiomers on its surface, exhibits intense chiroplasmonic activities (?40.2 ± 2.6 mdeg) in the visible region. These chiral SS nanoassemblies have high reactive oxygen species generating efficiency under circular polarized light illumination, resulting in a ¹O₂ quantum yield of 1.09. Meanwhile, it is found that SS could be utilized as PDT agent with remarkable efficiency under right circular polarized light irradiation in vitro and in vivo, allowing X‐ray computed tomography (CT) and photoacoustics (PA) imaging for tumors simultaneously. The achievements reveal that the enantiomer‐dependent and structure‐induced nanoassemblies play an important role in PDT effects. The present researches open up a new avenue for cancer diagnose and therapy using chiral nanostructures as multifunctional platform.     

Hard-templating of chiral TiO2 nanofibres with electron transition-based optical activity

The fabrication of optically active inorganic nanomaterials with chiral superstructures attracts attention because of their potential applications in chemical sensing and non-linear optics. Here, we present a facile way to prepare TiO₂ nanofibres, in which the nanocrystals are helically arranged into a chiral superstructure. Notably, the chiral superstructure shows strong optical activity due to the difference of absorbing left- and right-handed circularly polarized light. This special optical activity resulted from electron transition from the valence band to the conduction band of TiO₂ through a vicinal effect of helically arranged TiO₂ nanocrystals.     

Hard-templating of chiral TiO2 nanofibres with electron transition-based optical activity

Abstract

The fabrication of optically active inorganic nanomaterials with chiral superstructures attracts attention because of their potential applications in chemical sensing and non-linear optics. Here, we present a facile way to prepare TiO₂ nanofibres, in which the nanocrystals are helically arranged into a chiral superstructure. Notably, the chiral superstructure shows strong optical activity due to the difference of absorbing left- and right-handed circularly polarized light. This special optical activity resulted from electron transition from the valence band to the conduction band of TiO₂ through a vicinal effect of helically arranged TiO₂ nanocrystals.     

Magnetic and Electric Control of Circularly Polarized Emission through Tuning Chirality‐Generated Orbital Angular Momentum in Organic Helical Polymeric Nanofibers

Circularly polarized light emission promotes the development of smart photonic materials for advanced applications in chiral sensing and information storage. The orbital angular momentum is a unique property for organic chiral helical materials. In this work, a type of organic chiral polymeric nanowires is designed with strong chirality induced orbital angular momentum. Under the stimulus of an external magnetic field of 600 mT, circularly polarized emission from the chiral polymeric nanowire becomes more pronounced, where the g factor increases from 0.21 to 0.3. The observed phenomena mainly originate from the chirality‐dependent orbital angular momentum. Moreover, the orbital angular momentum in helical chiral nanowire structures can be suppressed by inhibiting electron transport in a helical way to diminish circularly polarized light emission at room temperature.     

Enzymatic Growth of Quantum Dots: Applications to Probe Glucose Oxidase and Horseradish Peroxidase and Sense Glucose

Three innovative assays are developed for the detection of enzymatic activities of glucose oxidase (GOx) and horseradish peroxidase (HRP) by the generation of CdS quantum dots (QDs) in situ using non‐conventional enzymatic reactions. In the first assay, GOx catalyzes the oxidation of 1‐thio‐β‐D ‐glucose to give 1‐thio‐β‐D ‐gluconic acid. The latter is spontaneously hydrolyzed to β‐D‐gluconic acid and H₂S, which in the presence of cadmium nitrate yields fluorescent CdS nanoparticles. In the second assay HRP catalyzes the oxidation of sodium thiosulfate with hydrogen peroxide generating H₂S and consequently CdS QDs. The combination of GOx with HRP, allowed quantification of glucose in plasma by following growth of fluorescent QDs.     

The Role of Surface Groups in Dictating the Chiral-Solvent-Induced Assembly of Carbon Dots into Structures Exhibiting Circularly Polarized Luminescence

Here, the use of achiral nanoparticles and solvent-induced chirality transfer is combined for the making of large structures exhibiting chiroptical properties in the form of circularly polarized luminescence (CPL). The nanoparticles that the authors use are carbon dots (C-Dots) that are known for their bright luminescence and the ability to tune their surface moieties by using different precursors in their synthesis. Here, the result of adding the chiral solvent limonene into an aqueous solution of various C-Dots is explored, differentiated by their surface group. It is shown that only nitrogen-containing C-Dots with amine functional groups see the emergence of a CPL signal and the formation of a large fibrillar assembled structure. The various forces happening in the interface between the C-Dots and the limonene phase and the role of the amine groups in both the chirality transfer interactions and the interactions between C-Dots in the assembly process are discussed, whereas these two processes intertwine with each other. The ability to form fluorescent chiral structures exhibiting CPL from achiral nanoparticles and the understanding of the various interactions in this process are both important to the rationale design of any supramolecular chiral assemblies.