Circularly Polarized Luminescence Research Articles

Chiral Co‐assembly Based on a Stimuli‐Responsive Polymer towards Amplified Full‐Color Circularly Polarized Luminescence

AbstractStimuli‐responsive circularly polarized luminescence (CPL) materials have been attaching wide attention in the field of optical information storage and encryption, while still facing the challenge of the realization of high luminescence dissymmetry factors (glum). This work presents a pair of stimuli‐responsive chiral co‐assemblies P7R3 and P7S3 by combining polymer PFIQ containing iso‐quinoline units with chiral inducers. The obtained chiral co‐assemblies can reversibly undergo significant modification in CPL behavior under trifluoroacetic acid (TFA) fumigation and annealing treatment, with the |glum| values exhibiting a reversible shift between 0.2 and 0.3. Moreover, the chiral co‐assemblies before TFA fumigating can effectively induce achiral emitters to generate intense full‐color CPL signals through CPL energy transfer (CPL‐ET), with the corresponding |glum| values larger than 0.2. Moreover, information encryption and decryption as well as a multi‐level logic gates application are achieved by leveraging the reversible stimuli‐responsive CPL activity of the chiral co‐assembly. This work provides a new perspective for the construction of stimuli‐responsive chiral luminescent materials with large |glum| values and the activation of CPL behavior in achiral emitters.

Chiral Rare-Earth (Ce, Eu) Metal Halides with Bright Circularly Polarized Luminescence.

Chiral metal halide materials are emerging chiroptical materials that are easy to synthesize and have a wide tunability. Rare-earth (RE) metals are desirable components to be incorporated in the hybrid regime; however, they are typically difficult to handle for solution-based halide chemistry. Here, we report two new examples of chiral RE metal halides with Ce(III) and Eu(III) with chiral alkanolammonium cations (R/S-3-hydroxyquinuclidium). These compounds crystallize in the non-centrosymmetric space group R3, where their mirror-like symmetric circular dichroism (CD) and circularly polarized luminescence (CPL) further witness the chiral nature. The superior emission properties, including the high photoluminescence quantum yield of the Ce-based materials (84-90%) and Eu-based materials (27-29%), have led to distinct and sharp symmetrical CPL in the ultraviolet and visible regions, with dissymmetry factors (glum) of ∼2 × 10-3 and ∼4 × 10-3, respectively. This work has established and expanded the materials space for chiral RE metal halides and demonstrated their potential for chiroptical and spintronic applications.

Enhanced Asymmetric Circularly Polarized Luminescence in Self-Organized Helical Superstructures Enabled by Macro-Chiral Liquid Crystal Quantum Dots.

Circularly polarized luminescent (CPL) materials have garnered considerable interest for a variety of advanced optical applications including 3D imaging, data encryption, and asymmetric catalysis. However, the development of high-performance CPL has been hindered by the absence of simple synthetic methods for chiral luminescent emitters that exhibit both high quantum yields and dissymmetry factors. In this study, we present an innovative approach for the synthesis of macro-chiral liquid crystal quantum dots (Ch-QDs/LC) and their CPL performance enhancement through doping with 4-cyano-4'-pentylbiphenyl (5CB), thus yielding a CPL-emitting generator (CEG). The Ch-QDs/LCs were synthesized, and their surfaces functionalized with a chiral mesogenic ligand, specifically cholesteryl benzoate, anchored via a lipoic acid linker. Under the regulation of chiral 2S-Zn2+ coordination complexes, the chiral LC encapsulation process promotes coordinated ligand substitution, resulting in an exceptional quantum yield of 56.3%. This is accompanied by high absorption dissymmetry factor (gabs) and luminescence dissymmetry factor (glum) values ranging from 10-3 to 10-2, surpassing most reported dissymmetry factors by at least an order of magnitude. The modular Ch-QDs/LCs demonstrate the ability to transfer chirality to the surrounding medium efficiently and manifest macro-chiral characteristics within a nematic LC matrix. Utilizing Ch-QDs/LC as an effective CPL emitter within achiral 5CB matrices enabled the system to achieve a maximum glum value of 0.35. The resultant CEG device acted as a direct CPL source, initiating enantioselective photopolymerization.

Three-Level Chirality Transfer and Amplification in Liquid Crystal Supramolecular Assembly for Achieving Full-Color and White 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.

Supramolecular Control of Helicene Circularly Polarized Luminescence Emitters in Molecular Solids and Bright Nanoparticles

AbstractCircularly polarized luminescence (CPL) from chiral molecules is attracting much attention due to its potential use in optical materials. However, formulation of CPL emitters as molecular solids typically deteriorates photophysical properties in the aggregated state leading to quenching and unpredictable changes in CPL behavior impeding materials development. To circumvent these shortcomings, a supramolecular approach can be used to isolate cationic dyes in a lattice of cyanostar‐anion complexes that suppress aggregation‐caused quenching and which we hypothesize can preserve the synthetically‐crafted chiroptical properties. Herein, we verify that supramolecular assembly of small‐molecule ionic isolation lattices (SMILES) allows translation of molecular ECD and CPL properties to solids. A series of cationic helicenes that display increasing chiroptical response is investigated. Crystal structures of three different packing motifs all show spatial isolation of dyes by the anion complexes. We observe the photophysical and chiroptical properties of all helicenes are seamlessly translated to water soluble nanoparticles by the SMILES method. Also, a DMQA helicene is used as FRET acceptor in SMILES nanoparticles of intensely absorbing rhodamine antennae to generate an 18‐fold boost in CPL brightness. These features offer promise for reliably accessing bright materials with programmable CPL properties.

Sign Inversion of Circularly Polarized Luminescence in Cholesteric Liquid Crystals Induced by Mercury Ions through Binaphthyl Dopants′ Conjugation Control

AbstractStimuli‐responsive circularly polarized luminescence (CPL) materials based on cholesteric liquid crystal (CLC) platforms show great promise for applications in information encryption and anticounterfeiting. In this study, we constructed a mercury ion‐responsive CPL system in CLCs by controlling the conjugation degree of axially chiral binaphthyl derivatives. Two chiral binaphthyl derivatives (R/S‐1 and R/S‐2) were initially used as chiral dopants to demonstrate that CPL inversion (glum values from 0.5/‐0.44 to −0.53/0.48) in CLCs could be achieved by modulating the conjugation degree of the chiral binaphthyls. Based on this concept, the thioacetal binaphthyl R‐2S was developed and used as a mercury‐responsive chiral dopant in CLCs. Under Hg ion treatment, the CPL sign inverted (glum value changed from 0.22 to −0.29) due to the transformation of the thioacetal into an aldehyde group. Additionally, the mercury ion‐responsive CPL material was applied in information encryption.

Enhancement of Circularly Polarized Luminescence Brightness of Schiff‐Base Diphenylboron and 9‐Borafluoren‐9‐yl Complexes

AbstractA series of diphenylboron and 9‐borafluoren‐9‐yl complexes with chiral Schiff‐base ligands was synthesized and characterized by NMR spectroscopy. X‐ray diffraction analysis revealed that their boron centers were adapted to tetrahedral coordination geometry. Although boron complexes with salicylideneimine backbones exhibited a weak circularly polarized luminescence (CPL), the CPL brightness (BCPL) was enhanced more than 9‐fold by the π‐extension of the Schiff base ligands. Time‐resolved emission decay analysis and theoretical calculations based on density functional theory (DFT) were conducted to further understand their luminescent properties.

Lantern-Shaped Structure Induced by Racemic Ligands in Red-Light-Emitting Metal Halide with Near 100 % Quantum Yield and Multiple-Stimulus Response.

Organic-inorganic metal halides (OIMHs) have become a research hotspot in recent years due to their excellent luminescent properties and tunable emission wavelengths. However, the development of efficient red-light-emitting OIMHs remains a significant challenge. This work reports three Mn-based OIMHs derived from 1-methyl-1,2,3,4-tetrahydroisoquinoline hydrobromide: racemic one (Rac-TBM) and chiral ones (R-TBM and S-TBM). As a result of the synergism of chiral organic ligands inducing a unique lantern-shaped hybrid structure containing both tetrahedra and octahedra, Rac-TBM exhibits red-light emission with near-unity luminescence quantum yield. In comparison, the chiral counterparts R/S-TBM display strong green emission and circularly polarized luminescence (CPL) with a glum value up to ±2.5×10-2. Interestingly, a mixture of R- and S-TBM can transform into Rac-TBM, successfully achieving a sensitive and reversible switch between red light of octahedra and green light of tetrahedra under external stimuli. The outstanding luminescent properties allow Rac-TBM to be utilized not only for X-ray radioluminescence with a detection limit down to 46.29 nGys-1, but also for advanced information encryption systems to achieve leak-proof decryption.

Lantern‐Shaped Structure Induced by Racemic Ligands in Red‐Light‐Emitting Metal Halide with Near 100 % Quantum Yield and Multiple‐Stimulus Response

AbstractOrganic‐inorganic metal halides (OIMHs) have become a research hotspot in recent years due to their excellent luminescent properties and tunable emission wavelengths. However, the development of efficient red‐light‐emitting OIMHs remains a significant challenge. This work reports three Mn‐based OIMHs derived from 1‐methyl‐1,2,3,4‐tetrahydroisoquinoline hydrobromide: racemic one (Rac‐TBM) and chiral ones (R‐TBM and S‐TBM). As a result of the synergism of chiral organic ligands inducing a unique lantern‐shaped hybrid structure containing both tetrahedra and octahedra, Rac‐TBM exhibits red‐light emission with near‐unity luminescence quantum yield. In comparison, the chiral counterparts R/S‐TBM display strong green emission and circularly polarized luminescence (CPL) with a glum value up to ±2.5×10−2. Interestingly, a mixture of R‐ and S‐TBM can transform into Rac‐TBM, successfully achieving a sensitive and reversible switch between red light of octahedra and green light of tetrahedra under external stimuli. The outstanding luminescent properties allow Rac‐TBM to be utilized not only for X‐ray radioluminescence with a detection limit down to 46.29 nGys−1, but also for advanced information encryption systems to achieve leak‐proof decryption.

Recent Advances of Boron‐Containing Chiral Luminescent Materials†

Comprehensive SummaryAs a class of organic dyes, boron‐containing compounds play an important role in organic luminescent materials. They have attracted considerable attention due to their unique photophysical properties. Chiral luminescent systems have a wide range of practical applications in biological imaging, optoelectronic devices, information storage and 3D display. Boron‐containing chiral luminescent materials can not only effectively improve the luminescent properties of CPL materials, but also bring unique properties to the system, which enables them to be used as favorable CPL emitting materials for an expanded range of applications. Here, we review the research progress of boron‐containing chiral luminescent materials by the detailed discuss according to different chiral skeletons, such as point chirality, 1,1’‐binaphthyl, [n]helicenes, [2,2]paracyclophane and pillar[5]arenes. We believe that this review is of significance for the development of boron‐containing compounds and CPL materials. Key ScientistsThe studies of circularly polarized luminescence (CPL) based on small organic molecules have advanced significantly. However, boron‐containing chiral luminescent materials have gained attention only in recent years. In 2019, Zhao's group prepared a binaphthalene derivative modified with triarylborane, representing the organic small molecule luminescent material to exhibit CPL characteristics responsive to both solvent and fluoride ions. In 2020, the Chen's group used the unique luminescence properties and steric effects of triarylborane and triphenylamine to prepare CPL materials based on the planar chiral pillar[5]arenes. In 2021, Wang's group developed a new class of B,N‐embedded double hetero[7]helicenes molecules that exhibit strong chiroptical responses in the UV‐visible region. In the same year, He's group used asymmetric reactions to synthesize boron‐based point‐chirality compounds with high efficiency and enantioselectivity. In 2023, Ravat synthesized 1,4‐B,N‐embedded helicenes exhibiting narrow‐band fluorescence and CPL. During this period, Matthias Wagner et al obtained (BO)2‐doped tetrathia[7]helicene via an efficient four‐step synthesis, and Zheng reported the nearly pure green circularly polarized electroluminescent device (CP‐OLED). In 2024, Chen's group prepared B,N‐embedded hetero‐[9]helicenes offering a pathway towards significantly enhanced efficiency in helicene‐based CPEL.

Processable Circularly Polarized Luminescence for the Synthesis of Chiral Plasmonic Nanoparticles

AbstractCircularly polarized light is previously shown as a chiral bias to enable the synthesis of chiral plasmonic nanomaterials through light‐matter interactions. The traditional approach for circularly polarized light generation relies on a “top‐down” approach by removing undesired light polarization through optics, which suffers from energy loss and compatibility issues. An alternative approach is to develop chiral phosphors that emit efficient circularly polarized luminescence (CPL). However, most materials fail to produce processable CPL with both high quantum yield and dissymmetry factors, let alone the synthesis of chiral nanomaterials. Herein, a liquid‐crystal‐templated framework is developed to assemble halide perovskite nanocrystals, CsPbX3 (X = Cl, Br, I), and achieved efficient CPL with the record‐high figure of merit (FM) for three primary colors (Red, Green, Blue). The fidelity of the CPL is further demonstrated in the synthesis of chiral gold nanoparticles, where a five‐fold increase in optical activity is achieved.

Multi‐Channel Optical Encryption Film With Strong Circularly Polarized Luminescence and High Quantum Yield

AbstractDeveloping a sustainable security module with multiple optical states is important to deter counterfeits, but is challenging. This work designs a kind of chiral luminescent film through the co‐assembly of the CNCs and d‐glucose, simultaneously doped with the lanthanide complex and organic dye. Superior mechanical performance makes it undertake various deformations, including twist, and tension without breaking. Meanwhile, this film has unique optical characteristics. On the one hand, the chiroptical signals can be manipulated through the matching of the photonic bandgap and fluorescence peak. On the other hand, due to the co‐assembly with two luminophores, the film displays the excitation wavelength (Ex)‐dependent circularly polarized luminescence properties. Under the Ex of 275 nm, the film simultaneously integrates a large dissymmetry factor of −0.3898, a high quantum yield of 69.19%, and a considerable lifetime of 1381 µs, which has exceeded most reported chiral luminescent assemblies. These multimodal and convertible optics endow the film with practical applications in the anti‐counterfeit. It can be designed as a security label or used as a written paper to encrypt the information. Even in humid surroundings, this security effect is still ensured.

Fluorescent Dye-Based Chiral Crystalline Organic Salt Networks for Circularly Polarized Luminescence.

A facile and general strategy is developed herein for the construction of circularly polarized luminescence (CPL) materials with simultaneously high fluorescence quantum efficiency (Φ) and large luminescence dissymmetry factor (glum). The self-assembly of fluorescent dye, disodium 4,4'-bis(2-sulfonatostyryl)biphenyl (CBS), with chiral diamines such as (R,R)/(S,S)-1,2-diaminocyclohexane (R/S-DACH) and R/S-1,2-diaminopropane (R/S-DAP), produces four chiral crystalline organic salt networks (COSNs). These as-synthesized organic salts emit strong blue-color CPL upon excitation, with both high Φ and glum values of up to 79% and 0.022. The well-defined molecular structures and arrangements of CBS are directly observed through single crystal X-ray analysis, offering crucial information regarding the origins of high-efficiency CPL performance. The chirality of amine is effectively transferred to CBS and further amplified to the supramolecular structure by multiple hydrogen bonding and π-π stacking interactions, giving rise to the large glum factors; meanwhile, the fixation and the ordered arrangement of CBS by these multiple interactions empower efficient suppression of molecular motions, facilitating strong fluorescence. This work can inspire the assembly of CPL organic materials with high Φ and glum via charge-assisted hydrogen bonds between fluorescent dyes and chiral inducers. It also offers important insight into the structural origins of supramolecular chirality and CPL performance.

Improved Energy Transfer in the Sensitization of Americium Enables Observation of Circularly Polarized Luminescence

AbstractThe first example of circularly polarized luminescence (CPL) from a molecular americium (Am) complex is reported. Coordination of Am(III) by a combination of thenoyltrifluoroacetonate and a chiral diphosphine oxide ligand yielded a complex with strong sensitized metal‐centered luminescence. The energy transfer process for sensitization appears to occur via a unique resonant pathway, which results in the removal of the overlap between ligand phosphorescence and sensitized Am luminescence that has often been observed. Owing to this feature, and despite the limited amount of material that could be used due to the radioactivity of 241Am, CPL could be measured. The collected luminescence and CPL spectra provide insight into the crystal field splitting of the 5D1→7F1 transition. These results pave the way for future studies of Am(III) luminescence to investigate electronic structure effects in this and other 5 f elements.

Hollow Superhelices Based on Chiral Europium Coordination Polymers.

The construction of helical nanotubes based on chiral coordination polymers (CPs) is an intriguing but challenging task, which is important for the development of functional materials that combine macroscopic chirality with tube-related properties. Here, we selected a chiral europium phosphonate system, e.g., Eu(NO3)3/R-,S-pempH2, and carried out a systematic work. By controlling the hydrothermal reaction conditions such as the pH value of the reaction mixture, the molar ratio and concentration of the reactants, we obtained block-like crystals of R/S-1b, rod-like crystals ofR/S-3r, hollow superhelices of R/S-2hh, and solid superhelices of R/S-4sh. In the latter two cases, the chirality has been successfully transferred and amplificated from the molecular level to the macroscopic level. Interestingly, compounds R/S-2hh and R/S-4sh have the same chemical composition of Eu(R/S-pempH)3×2H2O and show identical PXRD patterns, thus can be considered as the same material except for different morphologies. We further investigatedtheir circularly polarized luminescence (CPL) properties and found that the hollow superhelix of R/S-2hh had a larger dissymmetry factor than the solid superhelix of R/S-4sh. This study not only provides the first example of hollow superhelices of chiral CPs, but also offers the possibility of modulating the chiroptical properties of CPs through morphological control.

Rational Control of Maximum EMI/CPL Intensity and Wavelength of Bora[6]helicene via Polarity and Vibronic Effects.

Solvent polarity control as an efficient methodology to regulate the chiroptical properties, including spectral shape, width, intensity, wavelength, etc., has emerged as a novel frontier in optical materials design. However, the underling relationship connecting polarity to the optical property remains unclear. Herein, using state-of-the-art computations and the FC|VG model, the solvent effect on the chiroptical properties of bora[6]helicene was accurately and systematically computed to shed light on this issue. It is found that the vibronic coupling is crucial in explaining the spectral shape, width, and relative intensity of different peaks. Moreover, the intensity and position of the emission (EMI) and circularly polarized luminescence (CPL) are closely related to the polarity of the solvent. Intriguingly, we got a series of good linear relationships between polarity and EMI|CPL (|r| ≥ 0.95). Thus, this parameter can be used as a potential descriptor to estimate the intensity and position of EMI|CPL, leading to new strategies for designing fully colored fluorescent materials.

Ultra-Narrowband Circularly Polarized Luminescence from Multiple 1,4-Azaborine-Embedded Helical Nanographenes.

In this manuscript we present a strategy to achieve ultranarrowband circularly polarized luminescence (CPL) from multiple 1,4-azaborine-embedded helical nanographenes. The impact of number and position of boron and nitrogen atoms in the rigid core of the molecule on optical properties─including absorption and emission maxima, photoluminescence quantum yield, Stokes shift, excited singlet-triplet energy gap and full width at half-maximum (fwhm) for CPL and fluorescence─was investigated. The molecules reported here exhibits ultranarrowband fluorescence (fwhm 16-17.5 nm in toluene) and CPL (fwhm 18-19 nm in toluene). To the best of our knowledge, this is among the narrowest CPL for any organic molecule reported to date. Quantum chemical calculations, including computed CPL spectra involving vibronic contributions, provide valuable insights for future molecular design aimed at achieving narrowband CPL.

Chiral Amphiphilic Au23 Cluster and Its Specific Recognition to Remote Di-amines.

The atomic precision of metal nanoclusters and variability of surface ligands pave the way for their rational design and functionalization, whereas the property strengthening in multiple ways has been long challenging. Herein, improved amphiphilicity, chirality, thermostability, and strong CPL (circularly polarized luminescence) properties have been accomplished by facile ligand exchange of [Au23(CHT)16]- with HCapt (HCHT and HCapt denote cyclohexanethiol and captopril). In addition, the obtained chiral [Au23(SR)16]- (short for [Au23(CHT)16-x(Capt)x]-) clusters show specific binding affinity to remote-diamines (such as arginine and single/double strand DNA), originating from the hydrogen bonding and Van der Waals interaction among the surface Capt ligands and the di-amine groups.

5]Helicene Based π-Conjugated Macrocycles with Persistent Figure-Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence.

π-Conjugated chiral shape-persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one-pot synthesis of a series of chiral macrocycles with persistent figure-eight and Möbius shapes. Single-crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene-bridged figure-eight macrocycle, with its rigid, fully π-conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum| = 3.8 × 10-2) and significant CPL brightness (BCPL = 710.5 M-1cm-1). This method provides a versatile synthetic platform for producing various chiral D2-symmetric figure-eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.

5]Helicene Based π‐Conjugated Macrocycles with Persistent Figure‐Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence

π‐Conjugated chiral shape‐persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one‐pot synthesis of a series of chiral macrocycles with persistent figure‐eight and Möbius shapes. Single‐crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene‐bridged figure‐eight macrocycle, with its rigid, fully π‐conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum| = 3.8 × 10−2) and significant CPL brightness (BCPL = 710.5 M‐1cm‐1). This method provides a versatile synthetic platform for producing various chiral D2‐symmetric figure‐eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.