Circularly polarized lanthanide luminescence for advanced security inks

Ultra-High Optical Anisotropy with UV Transmission Achieved by Rational Arrangement of Extended π-Conjugated Groups

Birefringent material serves as a cornerstone in photonic applications, including optical communications, polarization control, and laser technologies. The development of birefringent materials with large birefringence (Δn > 0.3) and short ultraviolet (UV) cut-off edge (λcut-off edge < 400 nm) remains a significant challenge. Here, we demonstrate that properly aligned expanded π-conjugated groups provide a solution to balance the birefringence and UV transmittance. We report a new birefringent material, Li3(C9N13)·6H2O (LCN), in which the Li atoms and water molecules act as linkers to connect the birefringence-active group [C9N13]. This crystal material exhibits a giant optical anisotropy (Δnexp = 1.031 @ 546 nm), which is one of the highest among bulk crystal materials known to date. In addition, LCN shows a band gap of 3.62 eV, indicating its applicability in the UV optical range. Owing to favorable Li cation linkers and hydrogen bonding, the [C9N13] groups achieve a perfectly coplanar arrangement, thereby maximizing the optical anisotropy. This work offers a novel strategy for the rational design of advanced birefringent materials.

Circularly Polarized Luminescence Inversion Induced by Achiral Dyes in Organogels

Supramolecular assembly strategy is widely applied to develop circularly polarized luminescence (CPL) materials, especially for centrally chiral systems. The CPL sign of supramolecular gels based on a centrally chiral compound is generally regulated by employing the opposite chiral enantiomers. However, controlling CPL signals by regulating the interaction model between the achiral fluorophore and chiral gelator, accompanied by the adjustment of the emission wavelength, remains challenging. Herein, we have developed binary supramolecular gels based on achiral cyanostilbene derivatives and a chiral gelator. Two binary supramolecular gels have displayed achiral fluorophore-induced CPL sign inversion, attributed to the hydrogen bonding interaction between the carboxyl group of two fluorophores and the amino group of chiral gelator. This work reveals a rational approach to the design of CPL material with tunable CPL sign and CPL emission wavelength.

Superfluorescent upconversion nanoparticles as an emerging second generation quantum technology material

Superfluorescence (SF) in lanthanide doped upconversion nanoparticles (UCNPs) is a room-temperature quantum phenomenon, first discovered in 2022. In a SF process, the many emissive lanthanide ions within a single UCNP are coherently coupled by an ultra-short (ns or fs) high-power excitation laser pulse. This leads to a superposition of excited emissive states which decrease the emissive lifetime of the UCNP by a factor proportional to the square of the number of lanthanide ions which are coherently coupled. This results in a dramatic decrease in UCNP emission lifetime from the μs regime to the ns regime. Thus SF offers a tantalizing prospect to achieving superior upconversion photon flux in upconversion materials, with potential applications such as imaging and sensing. This perspective article contextualizes how SF-UCNPs can be regarded as a second generation quantum technology, and notes several challenges, opportunities, and open questions for the development of SF-UCNPs.

Multiple stimuli-responsive circularly polarized luminescent bio-composite films by coassembling cellulose nanocrystals and curcumin

Cellulose nanocrystal (CNC) -based circularly polarized luminescent (CPL) materials, which are responsive to external stimuli, have attracted increasing attention in developing smart chiral photonic materials. In this study, chiral nematic bio-composite CNC films with right-handed (R-) CPL emission and tunable dissymmetry factors (glum) were prepared by encapsulating curcumin in chiral nematic CNC films via an evaporation-induced self-assembly strategy. The CPL active bio-composite CNC films exhibit multiple responsiveness to relative humidity (RH) and pH. It is noted that the pH response of the composite films is visualized, which is reflected in the variation of film colors, fluorescence, and CPL emission wavelengths. Additionally, with a hydrophobic treatment, the bio-composite CNC films exhibit enhanced water resistance and pH-responsive CPL in acid/base aqueous solutions. Based on the responsive circular polarization information, the bio-composite CNC films were developed as optical labels for multiple anti-counterfeiting applications. The reported environmentally friendly bio-composite CNC films provide a new reference for utilizing natural polysaccharides to build multi-mode responsive CPL materials.

Acid/Base-Responsive Circularly Polarized Luminescence Emitters with Configurationally Stable Nitrogen Stereogenic Centers

A way to prevent the fast configurational interconversion of tertiary amines is to invoke Tröger's base analogs, which display methano- or ethano-bridged diazocine cores fused to aromatic rings. These derivatives are configurationally stable, even in acidic media when their structures bear ethylene bridges. Here, a two- to three-step synthesis is presented of methano- and ethano-bridged Tröger's base analogs with two peripheral fluorophores, i.e., anthracene, pyrene, and 9,9-dimethylfluorene units. These compounds, possessing two nitrogen stereogenic centers, exhibit good circularly polarized luminescence (CPL) dissymmetry factors (|glum| up to 1.2 × 10-3) and brightnesses (BCPL up to 26.3 M-1 cm-1), as well as excellent fluorescence quantum yields, demonstrating the Tröger´s base core to be a convenient scaffold to prepare CPL emitters upon functionalization with simple achiral fluorophores. Furthermore, the configurationally stable ethano-bridged Tröger's base analogs are employed to modulate their CPL response, generating a CPL switch through their protonation/deprotonation by consecutive additions of acid and base. The reversibility of the switching process is demonstrated for two cycles without altering the CPL performance of the molecule. It is believed that this straightforward and efficient approach to building CPL emitters employing the Tröger's base core could lead to its incorporation in CPL-based sensors and materials.

Circularly Polarized Luminescence From Spontaneous Symmetry Breaking in a Bimetallic Eu-Al Complex

The emergence of optically active functional compounds through spontaneous chiral symmetry breaking is a rare but intriguing phenomenon with relevance of both practical and fundamental interest. Here we show that a racemic Eu-Al compound, bearing only non-chiral ligands, forms a conglomerate upon crystallization. Single crystals of the compound are electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) active. Moreover, we found that a significant enantiomeric excess (50%) of either enantiomer is present in each crystallization batch (non-racemic conglomerate). Such spontaneous symmetry breaking leads not only to optically active single enantiomorph crystals but to an overall solid bulk with significant ECD and CPL.

Smart Lanthanide Metal-Organic Frameworks with Multicolor Luminescence Switching Induced by the Dynamic Adaptive Antenna Effect of Molecular Rotors

In this work, dynamic molecular rotors are used to construct smart lanthanide metal-organic frameworks (Ln-MOFs) emitters with adaptive antenna effects for the first time. The movement or distortion of the molecular rotors can be easily regulated by temperature changes, thereby inducing a dynamically changing antenna effect that can automatically match different lanthanide ions, achieving cyclic multicolor luminescence switching behavior and extremely complex multiple encryption anti-counterfeiting technology. In addition, by regulating the doping ratios of Gd(III) and Tb(III) with Eu(III) within the Ln-MOFs, differentiated energy transfer pathways are discovered, and red light emission very close to the BT.2020 color gamut standard is obtained. Gd0.99Eu0.01-MOF containing only 1% Eu(III) can show bright red luminescence, and in the range of 1-9% Eu(III) content, the characteristic emission intensity of Eu(III) ions and the content show an excellent linear relationship with a slope k as high as 2299. This can be used to identify the content of Eu(III) ions impurities in gadolinium salts from different manufacturers. Eu/Tb-MOF showed highly sensitive and visualized smart photoresponse behaviors to specific antibiotics and amino acids, respectively, with detection limits of 3.2/2.7 nM (tetracycline), 1.7/15.5 nM (oxytetracycline), 0.13/0.97 nM (aspartic acid), and 0.26/1.16 nM (glutamic acid).

Space-confined charge transfer turns on multicolor emission in metal-organic frameworks via pressure treatment

Single-component multi-emissive materials with stimuli-responsive properties offer unique advantages in the field of multicolor-tunable photoluminescence (PL). However, precisely modulating the emission of each component and achieving high-efficiency emission present a formidable challenge. Herein, we demonstrate that space-confined charge transfer (CT) turns on bright blue-green-white emission in initially faintly emissive metal-organic frameworks (MOFs) at ambient conditions through pressure treatments. Pressure treatments induce a transition from the initial long-range CT to a space-confined mode, significantly amplifying radiative transitions. Furthermore, the space-confined CT, which occurs between mutually perpendicular ligands, significantly influences the spin-orbit charge transfer intersystem crossing. Precise tuning of space-confined CT kinetics via multi-level pressure treatments allows us to modulate the fluorescence-to-phosphorescence ratio, achieving multicolor-tunable emission in the target MOFs. Our work advances the development of multicolor-tunable smart PL materials and unlocks the potential for their application in atmospheric environments.

Multilevel Intelligent Anti-Counterfeiting Label with Spatially Selective Dynamic Aurora Response and 3D Mesoscopic Physical Unclonable Function Fingerprint

With the increasing demand for anti-counterfeiting measures, the efficient integration of multi-level optical anti-counterfeiting information has become a critical challenge. In this study, a novel bottom-up self-assembly technique is introduced for fabricating composite integrated films. This method overcomes the size limitations of phosphors that achieve circularly polarized light (CPL) through co-assembly with cellulose nanocrystals. Specifically, rare earth metal-organic frameworks with a length of 140 µm can generate CPL with an asymmetry factor of 0.65. Moreover, the introduction of random defects in the film imparts unpredictable CPL properties, enabling dynamic auroral anti-counterfeiting within the decryption optical path. Additionally, an innovative two-stage serial decryption process is proposed by leveraging the non-correlation between orthogonal decryption patterns. Notably, the label surface features biomimetic fingerprint textures that exhibit 3D physical unclonable functions (PUFs) at the mesoscopic scale. These textures possess high entropy close to the ideal value of 1, and an encoding capacity in a 175 × 175 µm2 area reaches 262500. In summary, the composite label achieves a high degree of integration by combining three levels optical anti-counterfeiting information: full-chromatographic tunable photoluminescence, spatially selective random dynamic aurora responses, and 3D bionic mesoscopic PUFs fingerprints.

Intrinsically Luminescent Nematic Liquid Crystals Enabling High-Brightness Full-Color and White Circularly Polarized Luminescence via Chiral Coassembly

Circularly polarized luminescence (CPL) materials with simultaneous high dissymmetry factor (glum) and brightness are pivotal for advanced photonic applications but remain challenging due to inherent trade-offs betwwen glum value and photoluminescenc quantum yield (PLQY). Here, we report a supramolecular engineering strategy to construct intrinsically luminescent chiral nematic liquid crystal (N*-LC) films via coassembly of luminescent liquid crystals (LLCs) and chiral dopant. First, five intrinsic LLCs molecules (2PFQ, 2PFBQ, 2PFB, 2PFSe, and 2PFS) were synthesized by combining the biphenyl framework with dioctyl-functionalized fluorene, achieving exceptional nematic phases and high brightness with PLQY up to 99%. Then, chiral coassembly of the obtained LLCs with chiral dopants (P/M-THH) followed by rapid thermal quenching yielded Bragg reflection-free N*-LC films exhibiting high-brightness CPL with recorded glum values (up to 0.75) and PLQY (up to 71%). Full-color tunability and white CPL (CIE: 0.33, 0.33) were realized through precise compositional control. The simultaneous optimization of glum and PLQY enables high-brightness CPL with advanced anticounterfeiting capabilities, opening new avenues for developing high-brighness CPL materials for polarized photonic and optoelectronic applications.

Pathway-Dependent Control of Chiral Phases for Higher Performance and Inverted Circularly Polarized Luminescence

Chiral luminescent materials have garnered increasing attention for their exceptional ability to emit circularly polarized luminescence (CPL) along with their excellent applications. Here, a cyclohexylidene scaffold was conceptualized as a chiral source for developing higher-performance CPL materials in terms of simultaneously enhanced quantum yields (PLQYs) and dissymmetry factor. It was found that the axially chiral scaffold attached with a cyanostilbene showed a pathway-dependent assembly route to form chiral luminescent liquid crystals and crystals upon fast and slow cooling, respectively. A significant enhancement of PLQYs (98.4%) and a dissymmetry factor (glum) value (2.1 × 10-2), and consequently, a high figure of merit (FM) of up to 0.02 was achieved in the chiral liquid crystal phase. Moreover, the liquid crystal and crystal phases showed the opposite CPL signals while maintaining the same circular dichroism signs. Through a thorough evaluation of UV absorption, CPL emission, wide-angle X-ray diffraction, and theoretical calculations, it was revealed that the reversal of the CPL sign was linked to distinct phases of excited state molecular packing. This research utilized a novel intrinsically axially chiral source to develop a pathway-dependent and higher-performance CPL materials.

Achieving Dynamic Circularly Polarized Luminescence with 2D Hydrogen-Bonded Organic Frameworks

Significant advances have been made in the preparation and application of luminescent hydrogen-bonded organic frameworks (HOFs) in recent years. These materials exhibit unique structural flexibility in accommodating guest molecules, rendering them promising candidates for dynamic applications. Herein, a 2D HOF material is presented, constructed by the binary assembly of 5,5'-bis(azanediyl)oxalyl diisophthalic acid and tetra(pyrid-4-ylphenyl)ethylene to achieve dynamic circularly polarized luminescence (CPL) with the aid of chiral guests. Efficient chirality transfer and CPLs are realized by incorporating chiral carvone molecules into the 1D channels of HOFs through hydrogen bonding. As a result of the interlayer contraction upon guest desorption, these HOF materials display dynamic CPLs with emission colors varying from cyan to yellow. The method of the hydrogen bonding-enhanced host-guest chirality transfer in combination with the guest desorption-triggered interlayer contraction provides a simple method to achieve dynamic chiroptical properties with porous materials.

Organic Indium Halides with Near-Unity Photoluminescence Quantum Yields for Highly Efficient Luminescent Inks and White Light Emitting Diodes

Zero-dimensional (0D) organic indium halides have been emerged as promising broadband light emitters with wide application prospects, but most of the present halides suffer from low photoluminescence quantum yield (PLQY), and a high-power excitation light source is needed to obtain desirable performance. In this work, we elaborately select appropriate organic cations as crystal structural engineering and obtained a series of highly efficient 0D indium bromides. Under UV light excitation, these 0D indium halides display broadband yellow light emissions (550-600 nm) with near-unity PLQYs, which represents one of the highest values in all the previously reported indium halides. Benefiting from successful nanoscale engineering, highly luminescent inks based on these 0D indium halides are facilely prepared by dispersing nanocrystals into various organic solvents. The luminescent ink can be utilized to print various anticounterfeiting patterns, which displays photoreversible switching with visible/invisible transformation under the alternating irradiation of UV and visible light. Furthermore, white light emitting diodes can be fabricated with high color rendering index above 90 by using these 0D halides as down-conversion phosphors. This work not only promotes the development of indium halides but also significantly broadens the application in solid-state illumination and anticounterfeiting, etc.

Circularly Polarized Electroluminescence of Chiral Copper(I) Complexes of 1,1'-Binaphthalene-Functionalized 1,10-Phenanthroline

This study is dedicated to the design and synthesis of novel yellow-emitting Cu(I) complex enantiomers, R/S-Phen-Cu-POP, where the Cu(I) center is chelated by chiral 1,1'-binaphthalene-functionalized 1,10-phenanthroline (Phen) and bis(2-diphenylphosphinophenyl)ether (POP). Photophysical characterization revealed that the quantum yield (Φem) of R/S-Phen-Cu-POP in CH2Cl2 solutions was only 1.4-1.6%, but it significantly increased to 73.0% (R) and 76.1% (S) in PMMA doping films. Circularly polarized luminescence (CPL) studies demonstrated solid-state photoluminescence asymmetry factors (gPL) of R/S-Phen-Cu-POP were +8.5 × 10-3 and -8.6 × 10-3. Temperature-dependent emission spectra and lifetime studies identified a small singlet-triplet energy gap (ΔEST = 0.073 eV), which facilitates reverse intersystem crossing (RISC) from the triplet (T1) to the singlet (S1) state, thus leading to the transformation of phosphorescence at low temperature to thermally activated delayed fluorescence (TADF) at ambient temperature. Solution-processed organic light-emitting diodes (OLEDs) achieved a maximum luminance of 1270 or 1379 cd/m2, a current efficiency of 31.8 or 30.3 cd/A, a power efficiency of 14.8 or 14.4 lm/W, and an external quantum efficiency (EQE) of 11.9% or 11.3% for R-Phen-Cu-POP or S-Phen-Cu-POP, respectively. Furthermore, the devices displayed efficient circularly polarized electroluminescence (CPEL) with electroluminescence asymmetry factors (gEL) of +8.7 × 10-3 and -8.0 × 10-3 for R/S-Phen-Cu-POP.

Structural relaxation chirality transfer enhanced circularly polarized luminescence in heteronuclear CeIII-MnII complexes

Circularly polarized luminescence (CPL) materials have developed rapidly in recent years due to their wide application prospects in fields like 3D displays and anti-counterfeiting. Utilizing energy transfer processes to transfer chirality has been proven as an efficient way to obtain CPL materials. However, the physics behind energy-transfer induced CPL is still not clear. Herein, in a well-designed heteronuclear CeIII-MnII complex system [(Ce((R/S)-L)Br(μ-Br))2]MnBr4 [(R/S)-L = (2R,3R)- or (2S,3S)-2,3-dimethyl-1,4,7,10,13,16-hexaoxacyclooctadecane] with intra energy transfer from CeIII to MnII, the luminescence dissymmetry factor of MnII obtained by excitation of CeIII is around 10 times higher than that obtained by direct excitation of MnII, while the CeIII center itself shows an almost negligible CPL. To address this unusual phenomenon, we proposed a new mechanism named structural relaxation chirality transfer (SRCT) where structural relaxation of the excited chiral donor amplified chirality transfer to the acceptor by intramolecular interactions. As an assistant proof, a mixture of CeIII-ZnII and LaIII-MnII complexes with inter energy transfer showed no CPL amplification. These results will inspire more breakthroughs in the physics nature and development of energy-transfer induced CPL.

Algorithm in chemistry: molecular logic gate-based data protection

Data security is crucial for safeguarding the integrity, authenticity, and confidentiality of documents, currency, merchant labels, and other paper-based assets, which sequentially has a profound impact on personal privacy and even national security. High-security-level logic data protection paradigms are typically limited to software (digital circuits) and rarely applied to physical devices using stimuli-responsive materials (SRMs). The main reason is that most SRMs lack programmable and controllable switching behaviors. Traditional SRMs usually produce static, singular, and highly predictable signals in response to stimuli, restricting them to simple "BUFFER" or "INVERT" logic operations with a low security level. However, recent advancements in SRMs have collectively enabled dynamic, multidimensional, and less predictable output signals under external stimuli. This breakthrough paves the way for sophisticated encryption and anti-counterfeiting hardware based on SRMs with complicated logic operations and algorithms. This review focuses on SRM-based data protection, emphasizing the integration of intricate logic and algorithms in SRM-constructed hardware, rather than chemical or material structural evolutions. It also discusses current challenges and explores the future directions of the field-such as combining SRMs with artificial intelligence (AI). This review fills a gap in the existing literature and represents a pioneering step into the uncharted territory of SRM-based encryption and anti-counterfeiting technologies.

Chiral light-matter interactions in solution-processable semiconductors

Chirality is a fundamental property widely observed in nature, arising in objects without a proper rotation axis, therefore existing as forms with distinct handedness. This characteristic can profoundly impact the properties of materials and can enable new functionality, especially for spin-optoelectronics. Chirality enables asymmetric light and spin interactions in materials, with widespread potential applications ranging from energy-efficient displays, holography, imaging, and spin-selective and enantio-selective chemistry to quantum information technologies. This Review focuses on the emerging material class of solution-processable chiral semiconductors, a broad material class comprising organic, inorganic and hybrid materials. These exciting materials offer the opportunity to design desirable light-matter interactions based on symmetry rules, potentially enabling the simultaneous control of light, charge and spin. We briefly discuss the various types of solution-processible chiral semiconductors, including small molecules, polymers, supramolecular self-assemblies and halide perovskites. We then examine the interplay between chirality and spin in these materials, the various mechanisms of chiral light-matter interactions, and techniques utilized to characterize them. We conclude with current and future applications of chiral semiconductors that take advantage of their chiral light-matter interactions.

Helicene-Fluorescein Hybrids: A Reversible Base-Triggered (Chir)optical Switch with Sign Inversion of Circularly Polarized Luminescence

Novel circularly-polarized-luminescence (CPL) materials were designed and synthesized by integrating the intrinsic chirality of helicene with the acid/base-responsive properties of fluorescein. The synthesized helicene-fluorescein hybrids exhibit reversible switching between blue fluorescence under neutral conditions and red fluorescence under basic conditions. Furthermore, these hybrid compounds demonstrate unique chiroptical switching behavior with a rare base-triggered CPL sign inversion, where (P)-isomers show a negative CPL signal around 450 nm under neutral conditions and a positive signal around 620 nm under basic conditions, with three-fold enhanced dissymmetry factors (|glum|) under basic conditions. The structural basis for this switching was elucidated through TD-DFT calculations, revealing distinct angles between magnetic and electric transition dipole moments in closed versus open forms. Live-cell imaging experiments using HeLa cells revealed that the hybrid compounds exhibit intracellular red emission with minimal cytotoxicity, thus promising potential as chiral fluorescent probes for biological applications.

Flexible and rigid "chirally distorted" π-systems: binaphthyl conjugates as organic CPL-active chromophores

The inclusion of high-performance dyes into chiral π-conjugated systems is an effective strategy for activating significant chiroptical properties. We report the preparation and characterization of configurationally stable, axially-chiral π-conjugated systems in which acridone or 2,5-diarylamino-terephthalate has been fused into the chiral scaffold of a 1,1'-binaphthyl moiety. The high-yielding synthesis afforded π-conjugated systems with characteristics essentially matching those of the parent dyes while introducing detectable CPL activity in solution. In the acridone conjugate, good fluorescence is maintained in solution, but in the solid state, the distortion introduced by the binaphthyl system does not substantially help in restoring emissive properties; the flexibility and the emissive properties of the 2,5-diphenylamino-terephthalate chromophore are maintained in the conjugate. The new chiral chromophoric systems show absorption in the UV-vis domain, with good fluorescence properties in the visible range (quantum yields up to 23% and glum values up to 4 × 10-4).

Helix-induced full-color circularly polarized luminescence films with multiple information encryption and multi-stimuli responsiveness

The development of full-color circularly polarized luminescence (CPL) materials is of great significance in the field of luminescent materials; however, it is difficult due to the limitations in the synthesis and preparation methods. Helical polymers, with their high optical activity and easy processability, offer a promising solution for the construction of high-performance CPL materials. In this study, we successfully prepared full-color CPL composite films using precisely synthesized polyisocyanide (PI) as chiral source, poly(methyl methacrylate) as the matrix, and commercially available fluorescein as fluorescence source. The introduction of PI not only improves the mechanical properties and fluorescence lifetime of the composite films but also facilitates recyclability through centrifugation after dissolving the composite films with the poor solvent of PI. Moreover, the use of spiropyran as a red fluorescein allows for dynamic responsiveness to light, heat, and acid-base stimuli, broadening the functionality of the CPL materials and constructs a multiple information encryption system. This work presents a low-cost, easily processable, and multi-stimuli responsive strategy for full-color fabrication of CPL materials based on helical PI.

Hierarchical Self-Assembly of J-Aggregated 1,2-Bis(2-(benzyloxy)benzylidene) Hydrazine@2β-Cyclodextrin into Left-Handed Superhelix and Its External Stimuli-Responsive Unwinding

Induction of chirality to nanosized superstructures from hierarchical self-assembly of achiral monomeric units is an important area to understand the natural chiral amplification and evolution of life processes. We report herein that the complexation of salicylaldehyde azine, 1,2-bis(2-(benzyloxy)benzylidene)hydrazine (BSAZ), with β-cyclodextrin (β-CD) in aqueous solution results in the formation of a slipped J-aggregate (θ < 54.7°) that aggregates further into a left-handed superhelix through sterical constraints triggered by the hydrophobic effect. The structure of the monomeric BSAZ@2β-CD was elucidated by ultraviolet-visible (UV-vis), Fourier transform infrared spectroscopy (FT-IR), mass, powder X-ray diffraction (PXRD), and 1H, 13C, and 13C CP/MAS nuclear magnetic resonance (NMR) spectroscopy. The size, shape, and morphology of the self-aggregated hierarchy were evidenced by dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies. The system showed excellent aggregation induced circular dichroism (AICD) with a negative Cotton effect and a high fluorescence quantum yield of 0.33 at 620 nm in a poor solvent, water, because of the formation of a higher order excimer (N ≈ 46). The helical superstructure showed responsiveness under 254 nm UV light irradiation. Light irradiation slowly unwinds the supercoiled structure into a single strand, as was visualized by a SEM image taken after 15 min of continuous light irradiation. The excellent solvatochromic effect and the control over the formed hierarchical morphology show how a supramolecular approach tailored by noncovalent interactions can develop chiral superstructures from completely achiral molecular building blocks that would have a considerable practical value in chiroptics, templates, and chiral sensing.

Chiral europium halides with high-performance magnetic field tunable red circularly polarized luminescence at room temperature

Chiral organic-inorganic hybrid metal halides as promising circularly polarized luminescence (CPL) emitter candidates hold great potential for high-definition displays and future spin-optoelectronics. The recent challenge lies primarily in developing high-performance red CPL emitters. Here, coupling the f-f transition characteristics of trivalent europium ions (Eu3+) with chirality, we construct the chiral Eu-based halides, (R/S-3BrMBA)3EuCl6, which exhibit strong and predictable red emission with large photoluminescence quantum yield (59.8%), narrow bandwidth (≈2 nm), long lifetime (≈2 ms), together with large dissymmetry factor |glum| of 1.84 × 10-2. Compared with the previously reported chiral metal halides, these chiral Eu-based halides show the highest red CPL brightness. Furthermore, the degree of photoluminescence polarization in (R/S-3BrMBA)3EuCl6 can be manipulated by the external magnetic field. Particularly, benefiting from the field-generated Zeeman splitting and spin mixing at exciton states, an anomalously positive magneto-photoluminescence was observed at room temperature. This work provides an efficient strategy for constructing both high-performance and pure-red CPL emitters. It also opens the door for chiral rare-earth halides toward chiral optoelectronic and spintronic applications.

Thermally Invertible Full-Color Circularly Polarized Luminescence with High Dissymmetry Factors and High Quantum Yields in Fluorene Derivatives with Induced Chirality Generated in Chiral Liquid Crystals

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.

Contrasting Mechanochromic Luminescence of Enantiopure and Racemic Pyrenylprolinamides: Elucidating Solid-State Excimer Orientation by Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) and mechanochromic luminescence (MCL) have independently made substantial progress in recent years. However, the exploration of MCL in solid-state CPL materials, which holds practical significance, is still in its infancy. Herein, we report the MCL properties of readily accessible chiral pyrenylprolinamides bearing tert-butoxycarbonyl (Boc) or 2,2,2-trichloroethoxycarbonyl (Troc) groups. Enantiopure crystals of the Boc derivative display a greater MCL wavelength shift than racemic crystals, while the Troc derivative exhibit the opposite trend. Most notably, the enantiopure crystals show mechanochromic CPL. Unlike in previous examples, where CPL is quenched upon amorphization, robust CPL spectra were observed even in the amorphous states. By applying the excimer chirality rule, we have, for the first time, acquired insights into the excited-state structures within mechanically generated amorphous states. These findings offer a novel design strategy for developing mechanochromic CPL materials, paving the way for the future advancements in this emerging field.

2,3 : 6,7-Naphthalenediimide-Based Chiral Triangular Macrocycle: Self-Assembled Helix, Outer π-Surface Directed Co-Assembly and Circularly Polarized Luminescence

Here, we report the synthesis and self-assembly of a novel chiral 2,3 : 6,7-naphthalenediimide-based triangular macrocycle (NDI-Δ) and its chiroptical properties. The enantiomeric NDI-Δ is synthesized by condensation of (RR) or (SS)-trans-1,2-cyclohexanediamine and 2,3,6,7-naphthalenetetracarboxylic 2,3 : 6,7-dianhydride, in which the chirality of the macrocycles is controlled by the diamine. With the rigid outer π-surface, the macrocycle exhibits unique chiroptical properties and self-assembly modes. The NDI-Δ shows circularly polarized luminescence (CPL) in solution and can self-assemble into helical structures with the inversion of CPL signal and the enhancement of |glum|. Moreover, the NDI-Δ has a tailored electron-deficient outer π-surface, which can co-assemble with an electron-rich anthracene (AN) to form an intermolecular charge transfer (CT) complex, generating a yellow-green CT-CPL. Crystal structure analysis confirms that AN is mounted on the outer surface of NDI-Δ through π-π stacking and C-H ⋯ ${\cdots }$ π interactions. This work provides a critical example for the self-assembly of macrocycles into helical structures and outer π-surface directed CT complexes formation, opening up a new clue for designing chiral macrocycle-based chiroptical materials.

Versatile, Extrudable and Luminescent Tripodal BTA-Terpyridine (tpy) Gel Cross-Linked with d- and f-Block Metal Ions

The low molecular weight gelator (LMWG) 1 based on the tripodal benzene-1,3,5-tricarboxamide (BTA) motif, capped with terpyridine (tpy) units, was shown to form supramolecular gels with versatile functionalities such as self-healing, while the cross-linking of its fibers with d- and f-block metal ions led to modified photophysical properties, the obtained gels were additionally capable of extrusion.

Excitation-Dependent Circularly Polarized Luminescence Inversion Driven by Dichroic Competition of Achiral Dyes in Cholesteric Liquid Crystals

The development of stimuli-responsive chiral cholesteric liquid crystals (CLCs) materials holds significant potential for achieving three-dimensional (3D) anti-counterfeiting and multi-level information encryption. However, constructing phototunable CLCs systems with easy fabrication and fast response remains a great challenge. Herein, we exploit an excitation-dependent CLCs (ExD-CLCs) material by establishing dynamically photoresponsive dichroic competition between two achiral dyes: a negative dichroic dye (SP-COOH) and a positive dichroic dye (Nile Red, NR) within a CLCs medium. The ExD-CLCs exhibits a negative circularly polarized luminescence (CPL) signal (glum=-0.16) at 625 nm when excited at 365 nm. Remarkably, under excitation at 430 nm, the CPL signal is inverted, and the glum value increases to +0.26. Notably, the helical superstructure and handedness of the ExD-CLCs remain unchanged during this reversal process. The CPL signal reversal is driven by the dichroic competition between the SP-COOH dimer, which displays strong negative dichroism in its open-ring isomer form and silent negative dichroism in its closed-ring isomer form, and the NR dye, which exhibits static positive dichroism. Leveraging these excitation-dependent CPL properties, the quadruplex numerical anti-counterfeiting using ExD-CLCs is achieved.

Emerging devices based on chiral nanomaterials

As advanced materials, chiral nanomaterials have recently gained vast attention due to their special geometry-based physical and chemical properties. The fast development of the related science and technology means that various devices involving polarization-based information encryption, photoelectronic and spintronic devices, 3D displays, biomedical sensors and measurement, photonic engineering, electronic engineering, solar devices, etc., been explored extensively. These fields are at their beginning, and much effort needs to be made, including improving the optical, electronic, and magnetic properties of advanced chiral nanomaterials, precisely designing materials, and developing more efficient construction methods. This review tries to offer a whole picture of these state-of-the-art conditions in these fields and offers perspectives on future development.

Toward Rhenium-Based Circularly Polarized OLEDs Using Tailored Chiral Re(CO)3 Emitters

Chiral rhenium(I) emitters exhibiting circularly polarized phosphorescence (CPP) are an attractive mainstay for CP organic light-emitting diodes (CP-OLEDs). However, the efficiency of such emitters is not ideal, and they have never been explored for circularly polarized electroluminescence (CPEL) applications. Here, we have tailored robust chiral Re(I) complexes with improved CPP properties, and demonstrated CPEL from rhenium emitters for the first time. Two pairs of enantiomeric Re(I) complexes have been synthesized by introducing of one or two chiral menthol groups into 1,10-phenanthroline unit (phen) of archetypical emitters [ReBr(CO)3(phen)]. The designed complexes exhibit a yellow CPP with enhanced |glum| factors (up to 2.5×10-2) and a good quantum efficiency. The pioneering Re(I)-based CP-OLEDs (based on the obtained emitters) exhibit yellow CPEL with |gEL| factors of up to 6.2×10-3 and a maximal external quantum efficiency of 13.2 %. This work highlights the good potential of chiral Re(I) emitters for CPEL applications, and opens up a new shortcut to CPP-active Re(I) complexes.

Autoclave reactor synthesis of upconversion nanoparticles, unreported variables, and safety considerations

Autoclave reactors are widely used across chemical and biological sciences, including for the synthesis of upconversion nanoparticles (UCNPs) and other nanomaterials. Yet, the details of how autoclave reactors are used in such synthesis are rarely reported in the literature, leaving several key synthesis variables widely unreported and thereby hampering experimental reproducibility. In this perspective, we discuss the safety considerations of autoclave reactors and note that autoclaves should only be used if they are (a) purchased from reputable suppliers/manufacturers and (b) have been certified compliant with relevant safety standards. Ultimately, using unsuitable autoclave equipment can pose a severe physical hazard and may breach legal safety requirements. In addition, we highlight several parameters in autoclave synthesis that should be reported as standard to maximise the reproducibility of autoclave synthesis experiments across materials and chemistry research. We encourage users of autoclave synthesis vessels to: (1) adopt high-safety autoclaves and (2) report the many experimental variables involved to enhance experimental reproducibility.

Remote On-Paper Electrochemiluminescence-Based High-Safety and Multilevel Information Encryption

The escalating needs in information protection underscore the urgency of developing advanced encryption strategies. Herein we report a novel chemical approach that enables information encryption by on-paper electrochemiluminescence (ECL). Dendritic porous silica nanospheres modified with polyetherimide and bovine serum albumin were prepared as the chemical ink to write the secret message on a paper. Attaching the paper to an electrode, immersing it in a solution containing tris(2,2'-bipyridyl)ruthenium (Ru(bpy)3 2+) and then applying a suitable voltage, a remote "catalytic route" electrochemical reaction produces ECL that functions as the key to decrypt and visualize the message by imaging. In addition, proteins can be also used as the biological ink to write the secret message, which is then decrypted by a combined use of immunochemistry and ECL imaging as two keys. We believe the ECL-based strategy holds great promise in high-safety and multilevel information encryption, as it is protected not only by encoding, like conventional invisible inks, but also by the unique ECL decoding approach.

A rewritable and shape memory hydrogel doped with fluorescein-functionalized ZIF-8 for information storage and fluorescent anti-counterfeiting

The emergence of stimuli-responsive fluorescence anti-counterfeiting technology has garnered increasing attention in the era of intelligent internet. Smart fluorescent hydrogels combine the characteristics of luminous materials with the unique structure of hydrogels, offering the potential for dynamic reversible erasing and multi-tiered data encryption. In this work, a fluorescent hydrogel was constructed by zeolitic imidazolate framework-8 loaded with fluorescein and then mixed with polyvinyl alcohol hydrogel, sodium carboxymethyl cellulose and borax, which could be used for image hiding in visible light. The reversible bonds cross-linked fluorescent hydrogel was stretchable and self-healing with a three-dimensional network structure. The hydrogel presented bright green fluorescence under 365 nm UV light, which was quenched by adding copper ions. Meanwhile, the imprint of the hydrogel could be cleared by L-Cysteine and repeatedly recorded information many times. The alkali-induced shape memory capability was further utilized to achieve multi-tiered data encryption by deforming it to a 3D-specific shape through folding. The rewritable and multi-dimensional encrypted hydrogel is expected to improve data security and reduce resource consumption.

[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.

Rare Earth Complex-Based Functional Materials: From Molecular Design and Performance Regulation to Unique Applications

ConspectusRare earth (RE) elements, due to their unique electronic structures, exhibit excellent optical, electrical, and magnetic properties and thus have found widespread applications in the fields of electronics, optics, and biomedicine. A significant advancement in the use of RE elements is the formation of RE complexes. RE complexes, created by the coordination of RE ions with organic ligands, not only offer high molecular design flexibility but also incorporate features such as a broad absorption band and efficient energy transfer of organic ligands. Through the "antenna effect", organic ligands can transfer energy to RE ions, enhancing their luminescence efficiency. Moreover, the modification of the ligands can influence the local environment of the RE ions, thereby regulating their electronic structures and energy-level distributions. This makes it one of the important avenues for the efficient development and utilization of RE resources.The meticulous design of organic ligands during molecular synthesis enables the precise construction and regulation of RE complex structures, which are essential for probing molecular-level structure-performance relations and developing functional materials in fields such as optoelectronics, sensing, and catalysis/energy. Despite notable advancements, challenges persist in refining synthesis methodologies, innovating RE complex-based materials, enhancing stability, gaining better control over device functionality, and realizing high-value applications. This Account summarizes the recent advancements in molecular design and performance regulation achieved by our research group, particularly focusing on the synthesis and functional regulation of RE complex-based materials. We have employed strategies such as coordination self-assembly, in situ coordination, and microstructural evolution to achieve the precise synthesis and functional modulation of RE complex-based materials. These approaches have allowed us to finely tune properties such as the luminescence, electrical performance, and catalytic performance of various material systems. Consequently, we have made considerable strides in multidimensional optical information storage, the development of intelligent biological probes, the preparation of nanocatalysts, and the enhancement of inorganic-organic hybrid perovskite solar cell devices. Finally, we are committed to conducting an in-depth analysis of the challenges and opportunities that arise from the precise synthesis methods, performance regulation strategies, and innovative applications of RE complex-based functional materials. Additionally, we aim to propose potential solutions to current issues. This Account comprehensively summarizes the developments in RE complex-based materials to stimulate innovative thinking and new research directions and to establish a foundation for function-oriented precise synthesis methods.

Local Environment-Modulated f-f Transition in Unit-Cell-Sized Lanthanide Ultrathin Nanostructures

The regulation of the f-f transition is the basis of utilizing the abundant optical properties of lanthanide (Ln), of which the key is to modulate the local environment of Ln ions. Here, we constructed Eu(III)-based unit-cell-sized ultrathin nanowires (UCNWs) with red luminescence and polymer-like behavior, which appears as an ideal carrier for regulating f-f transition. The f-f transition of Eu(III) in UCNWs could be precisely regulated through various ligands. It is the unusual surface states that make the UCNWs exhibit greater electric dipole strength and better sensitivity to various ligands compared with the carefully constructed ultrathin nanosheets. In addition, the possibility of regulating f-f transition in UCNWs through energy transfer and a high entropy strategy was also revealed. Finally, a temperature-dependent universal fluorescent ink was prepared based on UCNWs, which provides ideas for intelligent flexible fluorescent materials.

Organic Circularly Polarized Room-Temperature Phosphorescence: Strategies, Applications and Challenges

Organic circularly polarized luminescence (CPL) plays crucial roles in chemistry and biology for the potential in chiral recognition, asymmetric catalysis, 3D displays, and biological probes. The long-lived luminescence, large Stokes shift, and unique chiroptical properties make organic circularly polarized room-temperature phosphorescence (CPP) a new research hotspot in recent years. Nevertheless, achieving high-performance organic CPP is still challenging due to the sensitivity and complexity of integrating triplet excitons and polarization within organic materials. This review summarizes the latest advances in organic CPP, ranging from design strategies and photophysical properties to underlying luminescence mechanisms and potential applications. Specifically, the design strategies for generating CPP are systemically categorized and discussed according to the interactions between chiral units and chromophores. The applications of organic CPP in organic light-emitting diodes, sensing, chiral recognition, afterglow displays, and information encryption are also illustrated. In addition, we present the current challenges and perspectives on developing organic CPP. We expect this review to provide some instructive design principles to fabricate high-performance organic CPP materials, offering an in-depth understanding of the luminescence mechanism and paving the way toward diverse practical applications.

Multicolor and sign-invertible circularly polarized luminescence from nonchiral charge-transfer complexes assembled with N-terminal aromatic amino acids

Circularly polarized luminescence (CPL) materials with precisely controlled emission colors and handedness are highly desirable for their promising applications in advanced optical technologies, but it is rather challenging to obtain them primarily due to the lack of convenient, powerful, and universal preparation strategies. Herein, we report a simple yet versatile solution route for constructing multicolor CPL materials with controllable handedness from nonchiral luminescent charge-transfer (CT) complexes through co-assembly with chiral N-terminal aromatic amino acids. The resulting ternary co-assemblies exhibit obvious CPL signals from 489 to 601 nm, covering from blue via green and yellow to orange-red. Notably, the CPL sign can be readily inverted by changing the substituents at the α-position of amino acids or the molecular structure of achiral electron donors due to effects on the hydrogen bonds, CT interactions, and stacking patterns. This work provides a new insight into developing CPL materials with tunable color and inverted handedness.

Enhanced Circularly Polarized Luminescence of Urea-Bridged Dimers of Axially Chiral BODIPY-Carbohydrate Hybrids

Herein, we report the synthesis of novel dimeric urea-bridged BODIPY-carbohydrate conjugates, which display circularly polarized luminescence (CPL). The dimers are composed of diastereomerically pure, axially chiral (P or M) BODIPY monomers containing a pendant glucose (d- or l-) unit. The latter was intended to add chirality, biocompatibility, and enhanced water solubility and facilitate the chromatographic resolution of the intermediate atropisomers. The dimerization process was based on the ureation reaction of azidomethyl BODIPYs. The rigorous structural assignment was possible by X-ray diffraction analysis of one of the BODIPY atropisomers.

Dynamic Control of Chiral Recognition in Water-Soluble Naphthotubes Induced by Hydrostatic Pressure

The dynamic control of chiral (enantiomeric) responses in chiral host-guest complexes through external stimuli is a significant challenge in modern chemistry for developing smart stimuli-responsive materials. Herein, we report the (chir)optical properties and chiral recognition behavior of water-soluble chiral naphthotubes (1) under the influence of hydrostatic pressure as an external stimulus. The hydrostatic pressure spectral profiles compared to those obtained at normal pressure revealed the dynamic behavior of 1 under hydrostatic pressure, owing to the flexible linker. In chiral recognition experiments, hydrophilic amino acids such as phenylalanine (Phe) and tryptophan (Trp) exhibited reaction volume changes (ΔV°) of -0.9 cm3 mol-1 for d-Phe, -1.2 cm3 mol-1 for l-Phe, -5.6 cm3 mol-1 for d-Trp, and -7.0 cm3 mol-1 for l-Trp, with enantioselectivity ranging from 1.2 to 1.6. In contrast, hydrophobic chiral styrene oxide (2) showed ΔV° values of 1.5 cm3 mol-1 for R-2 and 3.5 cm3 mol-1 for S- 2, with a relatively higher enantioselectivity of up to 7.6. These contrasting effects of hydrostatic pressure primarily originate from the dynamics of chiral naphthotubes.

Inversion of circularly polarized luminescence by electric current flow during transition

The development of chiral compounds exhibiting circularly polarized luminescence (CPL) has advanced remarkably in recent years. Designing CPL-active compounds requires an understanding of the electric transition dipole moment (μ) and the magnetic transition dipole moment (m) in the excited state. However, while the direction and magnitude of μ can, to some extent, be visually inferred from chemical structures, m remains elusive, posing challenges for direct predictions based on structural information. This study utilized binaphthol, a prominent chiral scaffold, and achieved CPL-sign inversion by strategically varying the substitution positions of phenylethynyl (PE) groups on the binaphthyl backbone, while maintaining consistent axial chirality. Theoretical investigation revealed that the substitution position of PE groups significantly affects the orientation of m in the excited state, leading to CPL-sign inversion. Furthermore, we propose that this CPL-sign inversion results from a reversal in the rotation of instantaneous current flow during the S1 → S0 transition, which in turn alters the orientation of m. The current flow can be predicted from the chemical structure, allowing anticipation of the properties of m and, consequently, the characteristics of CPL. This insight provides a new perspective in designing CPL-active compounds, particularly for C2-symmetric molecules where the S1 → S0 transition predominantly involves LUMO → HOMO transitions. If μ represents the directionality of electron movement during transitions, i.e., the "difference" in electron locations before and after transitions, then m could be represented as the "path" of electron movement based on the current flow during the transition.

Enhanced Circularly Polarized Green Luminescence Metrics from New Enantiopure Binary Tris-Pyrazolonate-Tb3+ Complexes

Achieving superior circularly polarized luminescence brightness (BCPL) is an important subject and continuous challenge for chiroptical materials. Herein, by applying a binary molecular design for the synthesis of chiral organo-Tb3+ molecules, a novel pair of mononuclear chiral tris-pyrazolate-Tb3+ enantiomers, [Tb(PMIP)3(R,R-Ph-PyBox)] (2) and [Tb(PMIP)3(S,S-Ph-PyBox)] (5), have been synthesized and characterized. The three 1-phenyl-3-methyl-4-(isobutyryl)-5-pyrazolone (HPMIP) ligands play the role of efficient luminescence sensitizers and strong light-harvesting antennas, while the enantiopure 2,6-bis(4-phenyl-2-oxazolin-2-yl) pyridine ligand (R,R/S,S-Ph-PyBox) is employed as the strong point-chiral inducer. With the proper combination of the HPMIP and Chiral-Ph-PyBox within the Tb3+ enantiomers, strong (PMIP)--centered π-π* electronic absorption (ε263 nm = 38,400-39,500 M-1 cm-1) and brilliant high-purity ligand-sensitized Tb3+-centered green luminescence (ΦPL = 47-48%) were observed. In addition, a clear circularly polarized luminescence (CPL) activity (|glum| = 0.096-0.103) was also observed, resulting in a strong BCPL (610-623 M-1 cm-1) for the two Tb3+ enantiomers from the hypersensitive transitions. Our results offer an effective path to develop high-performance chiroptical organo-Tb3+ luminophores.

Circularly Polarized Luminescence Bioimaging Using Chiral BODIPYs: A Model Scaffold for Advancing Unprecedented CPL Microscopy Using Small Full-Organic Probes

Unprecedented circularly polarized luminescence bioimaging (CPL-bioimaging) of live cells using small full-organic probes is first reported. These highly biocompatible and adaptable probes are pivotal to advance emerging CPL Laser-Scanning Confocal Microscopy (CPL-LSCM) as an undeniable tool to distinguish, monitor, and understand the role of chirality in the biological processes. The development of these probes was challenging due to the poor dichroic character associated with the involved CPL emissions. However, the known capability of the BODIPY dyes to be tuned to act as efficient fluorescence bioprobes, together with the capability of the BINOL-O-BODIPY scaffold to enable CPL, allowed the successful design of the first examples of this kind of CPL probes. Interestingly, the developed CPL probes were also multiphoton (MP) active, paving the way for the envisioned MP-CPL-bioimaging. The described full-organic CPL-probe scaffold, based on an optically and biologically tunable BODIPY core, which is chirally perturbed by an enantiopure BINOL moiety, represents, therefore, a simple and readily accessible structural design for advancing efficient CPL probes for bioimaging by CPL-LSCM.

Upconversion circularly polarized luminescence of cholesteric liquid crystal polymer networks with NaYF4:Yb,Tm UCNPs

Upconversion circularly polarized luminescence (UC-CPL) exhibits promising potential for application for anti-counterfeiting and displays. Upconversion nanoparticles (UCNPs), NaYF4:Yb,Tm, with uniform morphology and high crystallinity, were prepared via a simple solvothermal method. These UCNPs were embedded into cholesteric liquid crystal polymer network (CLCN) films. The UC-CPL performance of these films was investigated using left- and right-handed circular polarizers. After calibration, the |gcallum| values (up to 0.33) were obtained for the free-standing CLCN-UCNPs films, while a |gcallum| value of 0.43 was achieved for the CLCN-UCNPs-coated PET film. Moreover, a combined system comprising a PMMA-UCNPs layer and a CLCN layer yielded an ultra-large |gcallum| value of up to 1.73. Flexible and colourful patterned CLCN films were fabricated using photomasks, offering potential applications in anti-counterfeiting. This study not only successfully prepared UC-CPL-active materials based on CLCNs and UCNPs, but also demonstrated the chiral filtering effect of CLCN films in upconversion luminescent materials.

Boosting the circularly polarized luminescence of pyrene-tiaraed pillararenes through mechanically locking

Attributed to their unique dynamic planar chirality, pillar[n]arenes, particularly pillar[5]arenes, have evolved as promising platforms for diverse applications such as circularly polarized luminescence (CPL) emitters. However, due to the unit flipping and swing, the achievement of excellent CPL performances of pillar[5]arenes in solution state remains a formidable challenge. To deal with this key issue, a mechanically locking approach has been successfully developed, leading to boosted dissymmetry factor (glum) values of pyrene-tiaraed pillar[5]arenes up to 0.015 through the formation of corresponding [2]rotaxanes. More importantly, taking advantage of the stably locked co-conformers, these resultant [2]rotaxanes maintain excellent CPL performances in diverse solvents and wide range of concentrations, making them promising candidates for practical applications. According to this proof-of-concept study, we have not only successfully developed a powerful strategy for the rational design of chiral luminescent materials with desired CPL performances but also contributed a promising platform for the construction of smart chiral materials.

Highly Efficient Spectral Measurement Methods Using Newly Developed High-Throughput Magnetic Circularly Polarized Luminescence System

Magnetic circularly polarized luminescence (MCPL) spectroscopy is widely used to evaluate the luminescence dissymmetry factor (gMCPL) for compounds. However, even for the same instrument and operating conditions, the measured gMCPL is affected by errors associated with sources such as baseline drift and spectral noise, and so the range of variation of gMCPL must be considered when comparing values, which requires multiple measurements for the same sample. Also, because many samples undergo photodegradation under excitation light, it is difficult to accumulate and average spectra for samples with weak MCPL signals to improve the signal-to-noise ratio. Single measurements must therefore be performed on multiple samples and the results averaged. Furthermore, for samples with a small Stokes shift, spectral correction is required to compensate for the intensity reduction due to the inner-filter effect (IFE). Such measurements are generally performed manually and are therefore time consuming and prone to human error. Here, we demonstrate the use of a newly developed high-throughput MCPL system to automatically measure MCPL and fluorescence spectra of multiple samples of phthalocyanine complexes with high efficiency and reduced human errors. This system allows the incorporation of effective countermeasures to the issues of gMCPL variation, sample photodegradation, extremely weak MCPL signals, and the IFE.

Multi-Responsive Polymer Nanoparticles: A Versatile Platform for Double-Security Anticounterfeiting and Smart Food Packaging

Potential applications of colloidal polymer nanoparticles in the preparation of smart inks are investigated by physical incorporation of the oxazolidine molecules. Precise adjusting the polymer chain flexibility and polarity is achieved by controlling the ratio of methyl methacrylate and butyl acrylate monomers in the polymerization reaction. In addition, nanofibrous indicators of acid-base vapors are prepared from the latex nanoparticles. This can be beneficial for creating materials that sense and respond to environmental changes, such as humidity or moisture and acidity. Thermochromic inks are prepared by microencapsulating crystal violet lactone dye (CVL) in polymer matrices to prevent their release into the aqueous media. Combining two distinct systems with varying triggers, such as light and temperature, provides an effective strategy for double-encryption anticounterfeiting and crack and scratch detection and indication applications. Preparing labels impregnated with double-responsive inks, a novel approach is developed for food spoilage detection and preservation indication. Labels are manufactured using polymer nanoparticles, which contain photoluminescent oxazolidine molecules, as well as a trinary mixture of CVL within core-shell latex particles as the thermochromic dye. The combination of these two responsive elements transforms traditional packaging into a dynamic and interactive sentinel for the food it holds.

Living Hybrid Exciton Materials: Enhanced Fluorescence and Chiroptical Properties in Living Supramolecular Polymers with Strong Frenkel/Charge-Transfer Exciton Coupling

A family of chiral perylene diimides (PDIs) was newly developed as excellent circularly polarized luminescence (CPL) materials. They are asymmetrically derivatized with a double-alkyl-chained L- or D-glutamate unit and a linear or branched alkyl chain. When water is added to the tetrahydrofuran (THF) solution of glutamate-PDI-linear-alkyl chain compounds, kinetically formed H-aggregates are formed in globular nanoparticles (NPs). These NPs undergo spontaneous transformation into thermodynamically stable nanotubes via helical nanostructures, which showed structured broad spectra originating from the strong coupling of delocalized Frenkel excitations (FE) and charge transfer excitations (CTE). Significant enhancement of circular dichroism (CD), fluorescence quantum yield, and circularly polarized luminescence (CPL) with luminescence dissymmetry factor (glum) are observed during the transformation of NPs to the FE/CTE-coupled helical and tubular structures. This transformation process is significantly accelerated by applying physical stimuli, i.e., ultrasonication or adding helical aggregates as seed crystals, a feature unique to living supramolecular polymerization. Meanwhile, the branched chain-containing PDIs only form H-aggregates and did not show FE/CTE hybrid exciton states with living supramolecular polymerization properties. This study unveils that suitably designed chiral PDI derivatives show FE/CTE coupling accompanied by high fluorescence quantum yields, enhanced chiroptical properties, and supramolecular living polymerization characteristics.

Supramolecular chiroptical sensing of chiral species based on circularly polarized luminescence

Circularly polarized luminescence (CPL) refers to the differentiation of the left-handed and right-handed emissions of chiral systems in the excited state. Serving as an alternative characterization method to circular dichroism (CD), CPL can detect changes in fluorescence in a chiral system, which could be more efficient in recognizing chiral species. Although CPL can be generated by attaching luminophores to a chiral unit through a covalent bond, the non-covalent bonding of fluorescent chromophores with chiral species or helical nanostructures can also induce CPL and their changes. Thus, CPL can be used as an alternative detection technique for sensing chiral species. In this review, we summarize typical recent advances in chirality sensing based on CPL. The determination of the absolute configuration of chiral compounds and encrypted sensing is also discussed. We hope to provide useful and powerful insights into the construction of chemical sensors based on CPL.

Dual luminescence and infrared circularly polarized luminescence up to 900 nm with platinum complexes bearing a helical donor-acceptor ligand

Chiral molecular materials able to emit circularly polarized luminescence (CPL) have attracted considerable interest in the last few decades, due to the potential of CP-light in a wide range of applications. While CP luminescent molecules with blue, green, and yellow emissions are now well-reported, NIR CPL from organic and organometallic compounds lags behind due to the dual challenge of promoting radiative deexcitation of the excited state in this low energy region while assuring a significant magnetic dipole transition moment, a prerequisite for generating CPL. Based on a versatile axially chiral arylisoquinoline ligand, we report the synthesis and chiroptical properties of chiral donor-acceptor platinum(ii) complexes displaying CPL that extends up to almost 900 nm. Interestingly, these emitters show both fluorescence and phosphorescence emissions in solution, with intensities depending on the charge-transfer character of the organic ligand. Experimental and theoretical investigations show that this feature strongly impacts the intersystem crossing event between the singlet and triplet excited states of these complexes and the related phosphorescence lifetime. The effect is less important regarding the CPL, and most complexes show luminescence dissymmetry factors with values up to ca. 2 × 10-3 around 800 nm.

Air and Thermally Stable Fluoride Bridged Rare-Earth Clusters Showing Intense Photoluminescence and Potential LED Application

Fluoride based lattice is attractive for reducing phonon-induced quenching in rare-earth (RE) based luminescent materials. However, due to the strong affinity between RE and oxygen, the synthesis of fluoride-based complexes has to be protected under anhydrous conditions, and many known fluoride bridged RE clusters are unstable in air. Here, by using the "mixed-ligand" strategy a family of fluoride bridged RE clusters is synthesized, namely RE16(μ4-F)6(μ3-F)12(tBuCOO)18[N(CH2CH2O)3]4 (RE = Eu, EuFC-16; RE = Tb, TbFC-16), which are highly stable in air and decomposed thermally only when heating above 435 °C. Moreover, both clusters exhibit high photoluminescence quantum yields (PLQYEuFC-16 = 87.7%, PLQYTbFC-16 = 99.0%). Upon warming, EuFC-16 and TbFC-16 display excellent structural, thermal, and chroma stability. Thus, EuFC-16 and TbFC-16 have the potential to be used in light-emitting diode (LED) devices, offering many advantages over commercial phosphors. First, both clusters are soluble in UV-curable resin at any mixing rate, and the emission colors can be tuned from magenta, turquoise, willow green, and ivory to pure white if mixing blue phosphor BAM:Eu2+. Second, the clusters are hydrophobic, and the LEDs work well after soaking in water, indicating a good quality for outdoor lighting.