Loading Dyes into Chiral Cd/Zn‐Metal–Organic Frameworks for Efficient Full‐Color Circularly Polarized Luminescence

Host-guest chemistry of chiral metal-organic frameworks (MOFs) has endowed them with circularly polarized luminescence (CPL), it is still limited for MOFs to systematically tune full-color CPL emissions and sizes. This work directionally assembles the chiral ligands, metal sites and organic dyes to prepare a series of crystalline enantiomeric D/L-Cd/Zn-n MOFs (n=1~5, representing the adding amount of dyes), where D/L-Cd/Zn with the formula of Cd2(D/L-Cam)2(TPyPE) and Zn2(D/L-Cam)2(TPyPE) (D/L-Cam=D/L-camphoric acid, TPyPE=4,4',4'',4'''-(1,2-henediidenetetra-4,1-phenylene)tetrakis[pyridine]) were used as the chiral platforms. The framework-dye-enabled emission and through-space chirality transfer facilitate D/L-Cd/Zn-n bright full-color CPL activity. The ideal yellow CPL of D-Cd-5 and D-Zn-4, with |glum| as 4.9 × 10-3 and 1.3×10-3 and relatively high photoluminescence quantum yield of 40.79 % and 45.40 %, are further assembled into a white CPL light-emitting diode. The crystal sizes of D/L-Cd/Zn-n were found to be strongly correlated to the types and additional amounts of organic dyes, that the positive organic dyes allow for the preparation of > 7 mm bulks and negative dyes account for sub-20 μm particles. This work opens a new avenue to fabricate full-color emissive CPL composites and provides a potentially universal method for controlling the size of optical platforms.

Chirality Transfer from Chiral Mesoporous Silica to Perovskite CsPbBr ₃ Nanocrystals: The Role of Chiral Confinement

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

Tunable Multicolor Circularly Polarized Luminescence via Co-assembly of One Chiral Electron Acceptor with Various Donors

Chiral functional materials with circularly polarized luminescence (CPL) have risen rapidly in recent years because of their fascinating characteristics and potential applications in various research fields. CPL refers to the differential spontaneous emission of left (L)- and right (R)-handed circularly polarized light upon photon or electron excitation. Generally, an outstanding CPL-active material needs to possess a high luminescence dissymmetry factor (glum) (defined as 2(IL - IR)/(IL + IR) where I is the emission intensity), which is between -2 and +2. Although the exciting development in CPL-active materials was achieved, the modulation of CPL signs is still a challenge. For small organic systems, a relatively small glum value, one of the key parameters of CPL, limits their practical applications. Searching for efficient approaches for amplifying glum is important. Therefore, over the past decades, besides optimizing the structure of small molecules, many other strategies to obtain efficient CPL-active materials have been developed. For instance, self-assembly has been well demonstrated as an effective approach to amplify the supramolecular chirality as well as the glum values. On the other hand, chiral liquid crystals (CLCs), which are capable of selective reflection of left- and right-handed circularly polarized light, also to serve as a host matrix for endowing guest emitters with CPL activity and high glum values. However, self-assembly focuses on modulating the conformation and spatial arrangement of chiral emitters. And the CPL of a luminophore-doped CLC matrix depends on the helix pitch and band gap positions. Lately, novel photophysical approaches to modulate CPL signs have gradually emerged.In this Account, we discuss the recent progress of excited-state-regulation involved CPL-active materials. The emergence, amplification, and inversion of CPL can be adjusted through regulation of the excited state of chiral emitters. For example, Förster resonance energy transfer (FRET) can amplify the glum values of chiral energy acceptors in chiral supramolecular assemblies. By combining the concepts of photon upconversion and CPL, high-energy upconverted circularly polarized emission was achieved under excitation of low-energy light, accompanied by an amplified glum. In addition, the organic systems with unpaired electrons, i.e., charge transfer (CT) system and open-shell π-radical, show favorable CPL properties, which can be flexibly tuned with an applied magnetic field. It should be noted that these photophysical process are associated with the excited state of chiral emitters. So far, while the main focus is on the regulation of the molecular and supramolecular nanostructures, direct regulation of the excited state of the chiral system will serve as a new platform to understand and regulate the CPL activity and will be helpful to develop smart chiroptical materials.

Simple Double Hetero[5]helicenes Realize Highly Efficient and Narrowband Circularly Polarized Organic Light-Emitting Diodes

The practical application of the circularly polarized luminescence (CPL) emitted from chiral substances faces significant hurdles, primarily due to the small luminescence dissymmetry factor (glum) and low photoluminescence quantum yield (PLQY). Herein, we demonstrate a hierarchical system in which metal clusters exhibit excellent CPL performance, with both excellent glum factors and high PLQYs, thereby triggering enantioselective photopolymerization. Their CPL activities are sequentially amplified in different assembly forms induced by liquid crystals (LCs), and the maximum glum factor is increased by 1240 times, reaching a value of 1.24. The PLQYs of the metal clusters in different assembled states are sharply enhanced compared to that in the discrete state. Benefiting from the CPL performance of the metal clusters, their CPL was used to remotely regulate enantioselective polymerization, thus realizing light-to-matter chirality transfer. Impressively, upon incorporation of achiral luminophores, the polymer system is endowed with CPL through sequential chirality transfer. These innovative achievements open new avenues for the design and cutting-edge application of CPL-active metal clusters.

The development of circularly polarized luminescence (CPL) emitters with a luminescence dissymmetry factor (|glum|) approaching the theoretical limit of 2 remains a central challenge in chiral photonics. Herein, considerable glum values (1.48-1.65) were achieved in helicates (NMe4)2[Eu2(R/S-L1-4)4] (ΔΔ/ΛΛ-1-4) with different structural rigidity, as well as in crown ether-modified (NMe4)2[Eu2(R/S-L5)4] (ΔΔ/ΛΛ-5) that exhibits adjustable coordination geometry symmetry. Notably, encapsulating bulkier [NEt4]+ instead of a [NMe4]+ counterion within the inner cavity of ΔΔ/ΛΛ-2 further elevates |glum| to an unprecedented 1.71, the highest value for any chiral molecular emitter. While the NMe4-ΔΔ/ΛΛ-3 achieves an ultrahigh CPL brightness (BCPL = 3625 M-1 cm-1), resulting from its large glum value (1.63) and high quantum yield (ΦPL = 32%). Structural and spectroscopic analyses demonstrate that the high CPL activity originates from a conformationally rigidified square antiprismatic (SAP) geometry around the Eu(III) center. This structure and property relationship is vividly demonstrated by the crown-ether-functionalized ΔΔ-5, where gradual binding of Cs+ ions triggers a pronounced glum fluctuation (1.48 → 0.62 → 1.41) through a perturbation and subsequent restoration of the SAP environment. Furthermore, the multicrown-ether binding sites in ΔΔ-5 enable cooperative guest binding, facilitating the first naked-eye CPL recognition of the antispasmodic drug tizanidine. This work establishes rigidifying SAP configuration as a general design principle for maximizing the CPL activity of lanthanide complexes and opening avenues for advanced CPL applications.

Circularly polarized luminescence (CPL) is attractive in understanding the excited-state chirality and developing advanced materials. Herein, we propose a chiral reticular self-assembly strategy to unite achiral AIEgens, chirality donors, and metal ions to fabricate optically pure AIEgen metal-organic frameworks (MOFs) as efficient CPL materials. We have found that CPL activity of the single-crystal AIEgen MOF was generated by the framework-enabled strong emission from AIEgens and through-space chirality transfer from chirality donors to achiral AIEgens via metal-ion bridges. For the first time, a dual mechano-switched blue and red-shifted CPL activity was achieved via ultrasonication and grinding, which enabled the rotation or stacking change of AIEgen rotors with the intact homochiral framework. This work provided not only an insightful view of the aggregation induced emission (AIE) mechanism, but also an efficient and versatile strategy for the preparation of stimuli-responsive CPL materials.

Chiral metal‐organic frameworks (MOFs) are usually endowed by chiral linkers and/or guests. The strategy using chiral secondary building units in MOFs for solving the trade‐off of circularly polarized luminescence (CPL)‐active materials, high photoluminescence quantum yields (PLQYs) and high dissymmetry factors (|glum|) has not been demonstrated. This work directionally assembles predesigned chiral silver clusters with ACQ linkers through reticular chemistry. The nanoscale chirality of the cluster transmits through MOF's framework, where the linkers are arranged in a quasi‐parallel manner and are efficiently isolated and rigidified. Consequently, this backbone of chiral cluster‐based MOFs demonstrates superb CPL, high PLQYs of 50.3%, and |glum| of 1.2 × 10−2. Crystallographic analyses and DFT calculations show the quasi‐parallel arrangement manners of emitting linkers leading to a large angle between the electric and magnetic transition dipole moments, boosting CPL response. As compared, an ion‐pair‐direct assembly without interactions between linkers induces one‐ninth |glum| and one‐sixth PLQY values, further highlighting the merits of directional arrangement in reticular nets. In addition, a prototype CPL switching fabricated by a chiral framework is controlled through alternating ultraviolet and visible light. This work is expected to inspire the development of reticular chemistry for high‐performance chiroptical materials.

Preparation of twisted organic–inorganic hybrid silica bundles with circularly polarized luminescence by supramolecular templating polymerization

Ligand-induced chirality in asymmetric CdSe/CdS core-shell nanocrystals (NCs) has been extensively applied in chiral biosensors, regioselective syntheses and assemblies, circularly polarized luminescence (CPL), and chiroptic-based devices due to their excellent physiochemical properties, such as the tunable quantum confinement effects, surface functionality, and chemical stability. Herein, we present CdSe/CdS NCs with various morphologies such as nanoflowers, tadpoles, and dot/rods (DRs) with chirality induced by surface chiral ligands. The observed circular dichroism (CD) and CPL activities are closely associated with the geometrical characteristics of the nanostructures, such as the shell thickness and the aspect ratio of the CdSe/CdS NCs. Furthermore, in situ observations of the growth of tadpoles with a single tail indicate that the CD response is mainly attributed to the CdS shell, which has a maximum tail length of ∼45 nm (approximately λ/10 of the incident light wavelength). On the other hand, the CPL activity is only related to the CdSe core, and the activity benefits from a thin CdS shell with a relatively high photoluminescence quantum yield (QY). Further theoretical models demonstrated the aspect-ratio-dependent g-factor and QY variations in these asymmetric nanostructures. These findings provide insights into not only the asymmetric synthesis of CdSe/CdS NCs, but also the rational design of CdSe/CdS nanostructures with tunable CD and CPL activities.

Circularly polarized luminescence (CPL) plays an important role in the development of advanced optical devices. However, the design of CPL-active materials with a decent dissymmetry factor is still challenging. Here, we report CPL-active transparent thin films made from optically active ruthenium complexes [Ru(bpy)3]2+ embedded in chiral inorganic frameworks. Due to the unique chiral-in-chiral combination, the obtained [Ru(bpy)3][Zn2(C2O4)3] displays CPL activity with a dissymmetry factor of 5 × 10-3. The CPL measurements show that the luminescence dissymmetry factor can be effectively enhanced by one order of magnitude when an optically active [Ru(bpy)3]2+ complex is incorporated into a chiral inorganic framework compared to its solution form. This study not only emphasizes the potential of constructing CPL-active thin films with coordination polymers but also points out the importance of introducing extra chiral environment to improve the CPL effect.

Circularly polarized luminescence (CPL) has emerged as an intriguing photophysical phenomenon with potential applications in optoelectronics, bioimaging and anti-counterfeiting materials. Among various CPL-active molecules, chiral boron difluoride complexes have attracted considerable attention due to their structural versatility, tunable emission properties and high luminescence efficiencies. This review summarizes recent progress in the design, synthesis, and photophysical properties of chiral boron difluoride complexes exhibiting CPL. We highlight key structural motifs, including boron-dipyrromethenes (BODIPYs), boron β-diketonates and boranils that have been successfully employed to induce efficient CPL activity. Moreover, we discuss the relationships between molecular structure and CPL performance, the mechanisms underlying CPL generation, and emerging strategies to improve emission efficiency and chiroptical properties. Finally, future perspectives are outlined with an emphasis on the challenges and opportunities in developing next-generation CPL-active materials based on boron difluoride frameworks.

Circularly polarized luminescence (CPL) is an interesting phenomenon representing the unequal emission of left-handed and right-handed polarized light from an emitter. CPL is promising in chirality characterizations and various optical applications. Traditionally, research on CPL is centered on organic substances. In recent years, CPL present on inorganic ones has also become a nascent topic, which is significant to explore novel chirality- and luminescence-related properties and applications in inorganic materials. This minireview summarizes the recent progress on the following two aspects: 1) how to endow common inorganic luminophores with CPL activity; 2) how to use emerging chiral inorganic nanomaterials to design CPL-active systems. The general synthesis strategies, optical properties, applications and outlook of CPL-active inorganic materials are demonstrated.