Processable, High-Performance Circularly Polarized Luminescence Architectures for Information Interaction.

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

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.

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

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

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 light exhibits promising applications in future displays and photonic technologies. Circularly polarized luminescence (CPL) from chiral luminophores is an ideal approach to directly generating circularly polarized light, in which the energy loss induced by the circularly polarized filters can be reduced. Among various chiral luminophores, organic micro-/nano-structures have attracted increasing attention owing to the high quantum efficiency and luminescence dissymmetry factor. Herein, the recent progress of CPL from organic micro-/nano-structures is summarized. Firstly, the design principles of CPL-active organic micro-/nano-structures are expounded from the construction of micro-/nano-structure and the introduction of chirality. Based on these design principles, several typical organic micro-/nano-structures with CPL activity are introduced in detail, including self-assembly of small molecules, self-assembly of π-conjugated polymers, and self-assembly on micro-/nanoscale architectures. Subsequently, we discuss the external stimuli that can regulate CPL performance, including solvents, pH value, metal ions, mechanical force, and temperature. We also summarize the applications of CPL-active materials in organic light-emitting diodes, optical information processing, and chemical and biological sensing. Finally, the current challenges and prospects in this emerging field are presented. It is expected that this review will provide a guide for the design of excellent CPL-active materials.

Strategies for the enhancement of CPL properties

Circularly polarized luminescence (CPL) has attracted significant attention due to its broad application potential in information encryption, chiral sensing, and advanced optoelectronic technologies. However, the construction of CPL-active materials that simultaneously exhibit high luminescence dissymmetry factors and high photoluminescence quantum yields remains a central challenge in this field. Colloidal quantum dots (QDs) with excellent photophysical properties provide a promising opportunity to resolve this issue. Extensive efforts have been devoted to integrating CPL activity into inorganic QDs, leading to the development of a variety of CPL-active QD-based systems. In this work, we systematically summarize recent advances in construction strategies for CPL-active systems based on different types of QDs, including conventional semiconductor QDs and perovskite QDs. Both ligand-induced chiral responses in dispersed colloidal nanoparticles and their chiral assemblies constructed via templates or environments are discussed, followed by a comparative analysis of their respective advantages and limitations. The applications of CPL-active QDs in fields such as information encryption and three-dimensional display are further highlighted. Furthermore, we evaluate these systems using key performance metrics, including the luminescence dissymmetry factor and photoluminescence efficiency, as well as the emission wavelength range, and highlight the significant scientific and technological importance of developing CPL-active materials operating in the NIR-II region. Finally, we highlight that the integration of artificial intelligence-assisted design with precise structural regulation provides a promising pathway toward the development of CPL-active materials with both enhanced chiroptical properties and improved biosafety. We expect that this work can provide valuable insights and guidance for further research in this field.

Synthesis and properties of chiral liquid crystal copolymers with tunable circularly polarized luminescence

Chiral liquid crystal supramolecular assembly provides an ideal strategy for constructing excellent circularly polarized luminescence (CPL) materials. However, the chirality transfer in chiral liquid crystals normally occurs at two levels from the configurational chirality to the supramolecular phase chirality. The more precise and more levels of chirality transmission are fascinating but remain challenging. The present work reports the first success of three-level chirality transfer and amplification from configurationally point chirality of small molecules to conformationally helical chirality of helical polymers and finally to supramolecular phase chirality of cholesteric liquid crystals composed of chiral nonfluorescent polymers (P46) and nematic liquid crystals. Noticeably, the helical twisting power of P46 is five-fold larger than its monomer. Full-color and white CPL with maximum luminescence dissymmetry factor up to 1.54 and photoluminescence quantum yield up to 63.8% are realized utilizing helical supramolecular assembly combined with selective reflection mechanism. Also significantly, the electrically stimuli-responsive CPL switching device as well as anti-counterfeiting security, information encryption, and chiral logic gate applications are developed. This study deepens the understanding of chirality transfer and amplification across different hierarchical levels.

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

Deliberately targeted emission wavelengths, high quantum yields (QYs), and high luminescence dissymmetry factors (glum) are essential for chiral materials exhibiting circularly polarized luminescence (CPL). The addition of achiral luminophores to chiral nematic liquid crystals (N*-LCs) is a promising way to generate CPLs. We aimed to generate red-green-blue (RGB)- and white-colored CPLs by adding each of three types of fluorene-based luminescent molecules and their mixtures to N*-LCs. Herein, achiral fluorene-based derivatives with RGB emission colors were synthesized and added to N*-LCs containing alkylcyanobiphenyl- and alkylcyanoterphenyl-based N-LCs and an axially chiral binaphthyl dopant. A mixture of the RGB fluorene derivatives was subsequently prepared at an optimum mixing ratio and added to the N*-LCs. The fluorene-based derivatives dissolved in the N*-LCs exhibited induced CPLs of RGB and white colors with QY values of 60-90% and glum values of 0.5-1.0. The glum value of 1.0 is the highest among white CPLs reported thus far, and there are no examples that simultaneously exhibit both high QY and high glum. Furthermore, a mixture of the RGB fluorene derivatives was added to a temperature-responsive N*-LC containing a thermally invertible chiral compound, resulting in reversible thermal inversion of white CPL.

Materials with circularly polarized luminescence (CPL) activity have immense potential applications in molecular switches, optical sensors, information storage, asymmetric photosynthesis, 3D optical displays, biological probe, and spintronic devices. However, the achiral architectures of most of the luminophores severely limit their practical needs. Within this context, molecular ferroelectrics with striking chemical variability and structure-property flexibility bring light to the assembly of CPL-active ferroelectric materials. Herein, we report organic-inorganic perovskite enantiomorphic ferroelectrics, (R)- and (S)-3-(fluoropyrrolidinium)MnBr3, undergoing a 222F2-type ferroelectric phase transition at 273 K. Their mirror relationships are verified by both single-crystal X-ray diffraction and vibrational circular dichroism (VCD). Furthermore, the corresponding Cotton effect for two chiral crystals was captured by mirror CPL activity. This may be assigned to the inducing interaction between the achiral luminescent perovskite framework and chiral organic components. As far as we know, this is the first molecular ferroelectric with CPL activity. Accordingly, this will inspire intriguing research in molecular ferroelectrics with CPL activity and holds great potential for the development of new optoelectronic devices.

Chiral lanthanide complexes hold great potential in developing advanced circularly polarized luminescence (CPL) materials in the near-infrared (NIR) wavelength range. While various ligands, such as β-diketonates and biphenols, have been successfully used to sensitize NIR emission of lanthanide ions, little attention has been paid to regulating CPL behaviors via ligand modification. In this study, we report the synthesis, structure, luminescence, and chiroptical properties of a pair of novel air-stable Shibasaki-type Yb(III) enantiomers supported by 3,3'-fluorinated binaphthol (F2BINOL). Compared to their nonfluorinated counterparts, these fluorinated complexes exhibit larger dihedral angles between the two naphthyl moieties and more distorted octahedral coordination environments around the Yb(III) ion, leading to increased overall crystal field splitting. These structural modifications result in enhanced photophysical properties: the luminescence lifetime (τobs), sensitization efficiency (ηsens), and quantum yield (QY) improve from 2.1 µs, 38%, and 0.7% to 2.7 µs, 63%, and 1.8%, respectively. Additionally, the dissymmetry factor (glum) and CPL brightness (BCPL) at 963nm increase by 32% and one order of magnitude, respectively. The scope of such chemical modification is broad, potentially encompassing a variety of BINOL derivatives, offering a unique platform to further elucidate the relationship between structural and electronic properties and CPL activity in lanthanide systems.

The combination of circularly polarized luminescence (CPL) and pure-organic room temperature phosphorescence (RTP) potentially facilitates the construction of organic chiroptical optoelectronics and display materials, which however are challenging to use in realizing smart control of luminescent colors and switchable chiroptical properties. Here, we show a host-guest strategy to fabricate color-tunable RTP-based circularly polarized phosphorescence. Napthalimides were conjugated directly to chiral segments, of which supramolecular chirality and CPL activities in solid-states could be triggered by substituting bromine atoms on amines. Introducing tetracyanobenzene as an achiral host matrix via simple grinding would allow for the intersystem crossing to trigger red RTP and corresponding CPL by excitation lower than 320 nm, with a large Stokes shift more than 300 nm. The critical excitation wavelength of the RTP switch is determined by the absorbance of tetracyanobenzene. When the excitation wavelength was larger than 320 nm, blue fluorescence dominated with turned off RTP and CPL. The excitation wavelength-dependent RTP and CPL switch allows for detecting ultraviolet (UV) light, showing distinguishable red-blue luminescent color transition, accompanied by on/off RTP. Changing the host matrix from tetracyanobenzene to tricyanobenzene or dicyanobenzene could adjust the critical detecting wavelength limit from 320 to 300 nm. This work establishes a strategy to realize color-tunable, UV light detectable RTP and CPL under smart control.