Amplification of Circularly Polarized Luminescence through Triplet–Triplet Annihilation-Based Photon Upconversion

The Effects of Pore Defects in π-Extended Pentadecabenzo[9]helicene

The introduction of precise pore defects into nanocarbon structures results in the emergence of distinct physicochemical characteristics. However, there is a lack of research on non-planar chiral nanographene involving precise pore defects. Herein, we have developed two analogues to the π-extended pentadecabenzo[9]helicene (EP9H) containing embedded pore defects. Each molecules, namely extended dodecabenzo[7]helicene (ED7H; 1) or extended nonabenzo[5]helicene (EN5H; 2), exhibits dual-state emission. Significantly, the value of |glum| of 1 is exceptionally high at 1.41×10-2 in solution and BCPL as 254 M-1 cm-1. In PMMA film, |glum| of 1 is 8.56×10-3, and in powder film, it is 5.00×10-3. This study demonstrates that nanocarbon molecules with pore defects exhibit dual-state emission properties while maintaining quite good chiral luminescence properties. It was distinguished from the aggregation-caused quenching (ACQ) effect corresponding to the nanocarbon without embedded defect. Incorporating pore defects into chiral nanocarbon molecules also simplifies the synthesis process and enhances the solubility of the resulting product. These findings suggest that the introduction of pore defects can be a viable approach to improve nanocarbon molecules.

Induced Circularly Polarized Luminescence From 0D Quantum Dots by 2D Chiral Nanosheets

Materials with circularly polarized luminescence (CPL) exhibit great application potential in biological scenes such as cell imaging, optical probes, etc. However, most developed materials are non-aqueous and toxic, which seriously restricts their compatibility with the life systems. Thus, it is necessary to explore a water-based CPL system with high biocompatibility so that to promote the biologic application process. Herein, a facile and efficient route to achieve the CPL properties of a functional aqueous solution is demonstrated by the combination of 0D quantum dots (QDs) and 2D chiral nanosheets. Benefited by the specific absorption ability of nanosheets for left/right-handed CPL, the QDs adsorbed onto the surface of nanosheets through hydrogen bond interactions showed apparent CPL features. In addition, this system has a good extensibility as the CPL property can be effectively regulated by changing the kind of emissive QDs. More importantly, this water-based nano-composite with facile fabrication process (one-step mixing) is suitable for the real applications, which is undoubtedly beneficial for the further progress of functional CPL materials.

Enhancing Circularly Polarized Electroluminescence through Energy Transfer within a Chiral Polymer Host

Organic light-emitting diodes (OLEDs) that are able to emit high levels of circularly polarized (CP) light hold significant promise in numerous future technologies. Such devices require chiral emissive materials to enable CP electroluminescence. However, the vast majority of current OLED emitter classes, including the state-of-the-art triplet-harvesting thermally activated delayed fluorescence (TADF) materials, produce very low levels of CP electroluminescence. Here a host-guest strategy that allows for energy transfer between a chiral polymer host and a representative chiral TADF emitter is showcased. Such a mechanism results in a large amplification of the circular polarization of the emitter. As such, this study presents a promising avenue to further boost the performance of circularly polarized organic light-emitting diode devices, enabling their further development and eventual commercialization.

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.

Photon Upconversion Cooperates with Downshifting in Chiral Systems: Modulation, Amplification, and Applications of Circularly Polarized Luminescence

Circularly polarized luminescence (CPL)-active materials are increasingly recognized for their potential applications such as 3D imaging, data storage, and optoelectronic devices. Typically, CPL materials have required high-energy (HE) photons for excitation to emit low-energy (LE) circularly polarized light, a process known as downshifting CPL (DSCPL). However, the emergence of upconverted CPL (UCCPL), where the absorption of multi LE photons results in the emission of a single HE photon with circular polarization, has recently attracted considerable attention. This minireview highlights the intricate relationship between upconversion and CPL phenomena. During upconversion, the dissymmetry factor (glum) value can be improved in certain systems. Additionally, the integration of both LE and HE photons in upconversion-downshifting-synergistic systems offers avenues for dual-excitation or dual-emission CPL functionalities. More in detail, the emerging UCCPL based on various photon upconversion mechanisms and their synergy with DSCPL are introduced. Additionally, several examples that demonstrate the applications of UCCPL are presented to highlight the future opportunities.

Near-Infrared Circularly Polarized Luminescent Physical Unclonable Functions

Distinguished from traditional physical unclonable functions (PUFs), optical PUFs derive their encoded information from the optical properties of materials, offering distinct advantages, including solution processability, material versatility, and tunable luminescence performance. However, existing research on optical PUFs has predominantly centered on visible photoluminescence, while advanced optical PUFs based on higher-level covert light remain unexplored. In this study, we present optical PUFs based on the utilization of the covert light of near-infrared circularly polarized luminescence (NIR-CPL). This interesting property is achieved by incorporating Yb-doped metal halide perovskite nanocrystals (Yb-PeNCs) possessing NIR emission property into chiral imprinted photonic (CIP) films. By employing a solvent immersion method, we successfully integrated Yb-PeNCs into these CIP films, thereby creating an optically unclonable surface. The resulting NIR-CPL emission adds a layer of advanced security to the optical PUF systems. These findings underscore the potential of solution-processable chiral films to play a pivotal role in advancing the next generation of PUFs.

Ultraviolet Circularly Polarized Luminescence in Chiral Perovskite Nanoplatelet-Molecular Hybrids: Direct Binding Versus Efficient Triplet Energy Transfer

The development of ultraviolet circularly polarized light (UVCPL) sources has the potential to benefit plenty of practical applications but remains a challenge due to limitations in available material systems and a limited understanding of the excited state chirality transfer. Herein, by constructing hybrid structures of the chiral perovskite CsPbBr3 nanoplatelets and organic molecules, excited state chirality transfer is achieved, either via direct binding or triplet energy transfer, leading to efficient UVCPL emission. The underlying photophysical mechanisms of these two scenarios are clarified by comprehensive optical studies. Intriguingly, UVCPL realized via the triple energy transfer, followed by the triplet-triplet annihilation upconversion processes, demonstrates a 50-fold enhanced dissymmetry factor glum. Furthermore, stereoselective photopolymerization of diacetylene monomer is demonstrated by using such efficient UVCPL. This study provides both novel insights and a practical approach for realizing UVCPL, which can also be extended to other material systems and spectral regions, such as visible and near-infrared.

Supramolecular Annihilator with DPA Parallelly Arranged by Multiple Hydrogen-Bonding Interactions for Enhanced Triplet-Triplet Annihilation Upconversion

The triplet annihilator is a critical component for triplet-triplet annihilation upconversion (TTA-UC); both the photophysical properties of the annihilator and the intermolecular orientation have pivotal effects on the overall efficiency of TTA-UC. Herein, we synthesized two supramolecular annihilators A-1 and A-2 by grafting 9,10-diphenylanthracene (DPA) fragments, which have been widely used as triplet annihilators for TTA-UC, on a macrocyclic host-pillar[5]arenes. In A-1, the orientation of the two DPA units was random, while, in A-2, the two DPA units were pushed to a parallel arrangement by intramolecular hydrogen-bonding interactions. The two compounds showed very similar photophysical properties and host-guest binding affinities toward electron-deficient guests, but showed totally different TTA-UC emissions. The UC quantum yield of A-2 could be optimized to 13.7% when an alkyl ammonia chain-attaching sensitizer S-2 was used, while, for A-1, only 5.1% was achieved. Destroying the hydrogen-bonding interactions by adding MeOH to A-2 significantly decreased the UC emissions, demonstrating that the parallel orientations of the two DPA units contributed greatly to the TTA-UC emissions. These results should be beneficial for annihilator designs and provide a new promising strategy for enhancing TTA-UC emissions.

Linker-dependent control of the chiroptical properties of polymethylene-vaulted trans-bis[(β-iminomethyl)naphthoxy]platinum(II) complexes

The effects of polymethylene bridges on the chiroptical properties of trans-bis[(β-iminomethyl)naphthoxy]platinum(II) platforms were examined both experimentally and theoretically using newly designed planar chiral Pt analogues (1) having three-dimensional superstructures. A series of optically pure polymethylene-vaulted Pt complexes (R)- and (S)-1 were synthesized and characterized with regard to the chiroptical behaviour of the trans-bis[(β-iminomethyl)naphthoxy]platinum(II) platforms. These complexes were found to exhibit structure-dependent chiroptical characteristics in solution, such that the absolute values of specific rotation, the circular dichroism dissymmetry factor (gabs) and the circularly polarized luminescence dissymmetry factor (glum) all increased upon shortening the polymethylene bridges. Density functional theory and time dependent density functional theory calculations were used to analyse vaulted and non-vaulted complexes, which demonstrated that the present linker-dependent chiroptical properties resulted from constraint-induced changes in the square planar Pt coordination centres rather than from chiral distortion along the coordination platforms.

Near Infrared-II Excited Triplet Fusion Upconversion with Anti-Stokes Shift Approaching the Theoretical Limit

The anti-Stokes shift represents the capacity of photon upconversion to convert low-energy photons to high-energy photons. Although triplet exciton-mediated photon upconversion presents outstanding performance in solar energy harvesting, photoredox catalysis, stereoscopic 3D printing, and disease therapeutics, the interfacial multistep triplet exciton transfer leads to exciton energy loss to suppress the anti-Stokes shift. Here, we report near infrared-II (NIR-II) excitable triplet exciton-mediated photon upconversion using a hybrid photosensitizer consisting of lead sulfide quantum dots (PbS QDs) and new surface ligands of thiophene-substituted diketopyrrolopyrrole (Th-DPP). Under 1064 nm excitation, this photon upconversion revealed a record-corrected upconversion efficiency of 0.37% (normalized to 100%), with the anti-Stokes shift (1.07 eV) approaching the theoretical limit (1.17 eV). The observation of this unexpected result is due to our discovery of the presence of a weak interaction between the sulfur atom on Th-DPP and Pb2+ on the PbS QDs surface, facilitating electronic coupling between PbS QDs and Th-DPP, such that the realization of triplet exciton transfer efficiency is close to 100% even when the energy gap is as small as 0.04 eV. With this premise, this photon upconversion as a photocatalyst enables the production of standing organic gel via photopolymerization under 1064 nm illumination, displaying NIR-II photon-driven photoredox catalysis. This research not only establishes the foundation for enhancing the performance of NIR-II excitable photonic upconversion but also promotes its development in photonics and photoredox catalysis.

Circularly polarized luminescence in quantum dot-based materials

Quantum dots (QDs) have emerged as fantastic luminescent nanomaterials with significant potential due to their unique photoluminescence properties. With the rapid development of circularly polarized luminescence (CPL) materials, many researchers have associated QDs with the CPL property, resulting in numerous novel CPL-active QD-containing materials in recent years. The present work reviews the latest advances in CPL-active QD-based materials, which are classified based on the types of QDs, including perovskite QDs, carbon dots, and colloidal semiconductor QDs. The applications of CPL-active QD-based materials in biological, optoelectronic, and anti-counterfeiting fields are also discussed. Additionally, the current challenges and future perspectives in this field are summarized. This review article is expected to stimulate more unprecedented achievements based on CPL-active QD-based materials, thus further promoting their future practical applications.

Azaborahelicene fluorophores derived from four-coordinate N,C-boron chelates: synthesis, photophysical and chiroptical properties

A series of six azaborahelicenes with varying electron-donor substitution at the 4-position of the aryl residue (i.e., naphthyl) or with variable π-extension of the aryl residue (thianthrenyl, anthryl, pyrenyl) was prepared with an efficient and flexible synthetic protocol. These different types of functionalization afforded notably pronounced intramolecular charge-transfer (ICT) character for the dyes with the strongest electron donor substitution (NMe2) or easiest to oxidize aryl residues, as evidenced by photophysical investigations. These effects also impact the corresponding chiroptical properties of the separated M- and P-enantiomers, which notably display circularly polarized luminescence (CPL) with dissymmetry factors in the order of magnitude of 10-4 to 10-3. Theoretical calculations confirm the optical spectroscopy data and are in agreement with the proposed involvement of ICT processes.

Aggregation-Induced Fluorescence Upconversion of Pyrene under Low Fluence: In Solutions and Polymeric Nanoparticles

In this study, aggregation-induced photon upconversion (iPUC) is demonstrated in the small polyaromatic molecule, pyrene. In binary-solvent mixtures, water, which induces the aggregation of polyaromatic molecules, assisted in triplet-triplet annihilation-based upconversion. No upconverted emission was observed in a dry solvent. Although upconverted emission in the absence of a triplet sensitizer was assigned to pyrene-aggregate-induced sensitization, the presence of a triplet sensitizer enhanced the upconversion efficiency. This experimental finding was further simulated to explore the possibility of iPUC in the condensed-phase polymer matrix. We studied 2-aminoethyl methacrylate hydrochloride-polystyrene copolymer nanoparticles embedded with the molecular upconversion system. The nanoparticle iPUC agreed with the proposition that water domains were present in polymer nanoparticles and helped aggregate pyrene in the host polymer. Despite the low systemic upconversion efficiency, this study provides a method for achieving fluorescence upconversion in relatively simple systems.

A Breakthrough in Solution-Processed Ultra-Deep-Blue HLCT OLEDs: A Record External Quantum Efficiency Exceeding 10% Based on Novel V-Shaped Emitters

It is always a great challenge to achieve high-efficiency solution-processed ultra-deep-blue organic light-emitting diodes (OLEDs) with the Commission Internationale de l'Eclairage (CIE) 1931 chromaticity coordinates matching the blue primary of Rec. International Telecommunication Union-Radiocommunication BT.2100, which specifies high dynamic range television image parameters. Inspired by hybrid local and charge transfer (HLCT) excited state emitters improving exciton utilization through high-lying reverse intersystem crossing, here, a series of high-performance blue emitters by a V-shaped symmetric donor (D)-π-acceptor (A)-π-D design strategy are developed. Here, the large torsions and unstable bonds of D-A structures can be improved through π bridges, and also the conjugation length and donor groups can be easily adjusted. The obtained emitters merit excellent photophysical and electrochemical properties, thermal stability, solution processibility, and HLCT excited state excellence. Results suggest that the OLEDs based on the obtained blue emitters all achieve high maximum external quantum efficiency (EQEmax ) of more than 8% with very low efficiency roll-off. In particular, the device based on 4',5'-bis(4-(9H-carbazol-9-yl)phenyl)spiro[fluorene-9,2'-imidazole] exhibits a satisfactory ultra-deep-blue emission (CIEx , y = 0.1579, 0.0387) and a record-high EQEmax (10.40%) among solution-processed HLCT OLEDs, which is very close to the record EQEmax of devices by vacuum vapor deposition technology.

Enhancement of Circularly Polarized Luminescence from Pulsating Nanotubules

Enhancing the dissymmetry factor (glum ) is a crucial issue in developing circularly polarized luminescence (CPL) materials. Herein, based on supramolecular self-assembly of diethyl l-glutamate-cyanodiarylethene (L-GC) in mixed solution of EtOH-H2 O with different water fraction, enhanced circularly polarized emission from pulsating nanotubules is realized. In the mixture of ethanol and water (30/70, v/v), L-GC self-assembles into roll-up-type dense nanotubes and shows l-CPL. Remarkably, by increasing the water fraction to 80% and 90%, the diameter of the roll-up nanotubes increases and the dissymmetry factor of the nanotubes is significantly enhanced from 6.9 × 10-3  (dense nanotubes) to 3.7 × 10-2 (loose nanotubes) because of the enhanced intermolecular interactions and more ordered supramolecular stacking when increasing the water fraction. An efficient way is provided here to realize the increase of the dissymmetry factor by only changing the composition of solvents.

Fundamentals, Advances, and Artifacts in Circularly Polarized Luminescence (CPL) Spectroscopy

Objects are chiral when they cannot be superimposed with their mirror image. Materials can emit chiral light with an excess of right- or left-handed circular polarization. This circularly polarized luminescence (CPL) is key to promising future applications, such as highly efficient displays, holography, sensing, enantiospecific discrimination, synthesis of drugs, quantum computing, and cryptography. Here, a practical guide to CPL spectroscopy is provided. First, the fundamentals of the technique are laid out and a detailed account of recent experimental advances to achieve highly sensitive and accurate measurements is given, including all corrections required to obtain reliable results. Then the most common artifacts and pitfalls are discussed, especially for the study of thin films, for example, based on molecules, polymers, or halide perovskites, as opposed to dilute solutions of emitters. To facilitate the adoption by others, custom operating software is made publicly available, equipping the reader with the tools needed for successful and accurate CPL determination.

Enhancing Circularly Polarized Phosphorescence via Integrated Top-Down and Bottom-Up Approach

In the dynamic domain of chiroptical technologies, it is imperative to engineer emitters endowed with circularly polarized luminescence (CPL) properties. This research demonstrates an advancement by employing a combined top-down and bottom-up strategy for the simultaneous amplification of photoluminescence quantum yield (Φ) and the luminescence dissymmetry factor (glum ). Square-planar Pt(II) complexes form helical assemblies, driven by torsional strain induced by bis(nonyl) chains. Integration of chiral anions leads these assemblies to prefer distinct helical sense. This arrangement activates the metal-metal-to-ligand charge transfer (MMLCT) transition that is CPL-active, with Φ and |glum | observing an upswing contingent on the charge number and aryl substituents in chiral anions. Utilizing the soft-lithographic micromolding in capillaries technique, we could fabricate exquisitely-ordered, one-dimensional co-assemblies to achieve the metrics to Φ of 0.32 and |glum | of 0.13. Finally, our spectroscopic research elucidates the underlying mechanism for the dual amplification, making a significant stride in the advancement of CPL-active emitters.

Recyclable soft photonic crystal film with overall improved circularly polarized luminescence

Existing circularly polarized luminescence materials can hardly satisfy the requirements of both large luminescence dissymmetry factor and high luminescent quantum yield, which hinders their practical applications. Here, we present a soft photonic crystal film embedded with chiral nanopores that possesses excellent circularly polarized luminescence performance with a high luminescence dissymmetry factor as well as a large luminescent quantum yield when loaded with various luminescent dyes. Benefitting from the retention of chiral nanopores imprinted from a chiral liquid crystal arrangement, the chiral soft photonic crystal film can not only endow dyes with chiral properties, but also effectively avoid severe aggregation of guest dye molecules. More importantly, the soft photonic crystal film can be recycled many times by loading and eluting guest dye molecules while retaining good stability as well as circularly polarized luminescence performance, enabling various applications, including smart windows, multi-color circularly polarized luminescence and anticounterfeiting.

Chiroptical Amplification of Induced Circularly Polarized Luminescence in Nucleotide-Templated Supramolecular Polymer

Efficient circularly polarized luminescence (CPL) from purely organic molecules holds great promise for applications in displays, sensing, and bioimaging. However, achieving high dissymmetry values (glum ) from organic chromophores remains a significant challenge. Herein, we present a bioinspired approach using adenosine triphosphate (ATP)-triggered supramolecular polymerization of a naphthalene diimide-derived monomer (ANSG) to induce CPL with a remarkable glum value of 1.1×10-2 . The ANSG molecules undergo a templated, chiral self-assembly through a cooperative growth mechanism in the presence of ATP, resulting in scrolled nanotubes with aggregation-induced enhanced emission (AIEE) and induced CPL. Furthermore, we demonstrate the concept of chiroptical amplification of induced CPL by efficiently amplifying asymmetry using a mixture of chiral ATP and achiral pyrophosphate. This innovative approach opens numerous opportunities in the emerging field of circularly polarized luminescence.

DNA-induced circularly polarized luminescence of helicene racemates

Enantiopure helicenes have been extensively investigated due to their outstanding chiroptical properties, while helicene racemates are considered as chiroptically silent. Here, we describe a facile method to produce circularly polarized luminescence (CPL) from helicene racemates via supramolecular association with DNA in aqueous solution. Racemic cationic helicene derivatives are immobilized in the grooves of commercially available double-stranded right-handed DNA, and the discrimination of left- and right-handed helicenes by chiral DNA is monitored by single molecule force spectroscopy. This subsequently leads to the generation of prominent CPL with dissymmetric factor |glum | of close to 0.01, which is approximate to enantiopure helicenes. The strategy developed in this work avoids the tedious and expensive chiral resolution process and provides a distinctive insight into the fabrication of CPL-emitting systems.

Liquid Crystals Doped with Chiral Fluorescent Polymer: Multi-Color Circularly Polarized Fluorescence and Room-Temperature Phosphorescence with High Dissymmetry Factor and Anti-Counterfeiting Application

Chiral nematic liquid crystals (N*-LCs) can tremendously amplify circularly polarized luminescence (CPL) signals. Doped emissive N*-LCs have been substantially explored. However, their CPL performances still need to be improved, mainly due to the unsatisfying helical twisting power (HTP) of commonly used chiral fluorescent dopants. Chiral fluorescent helical polymers (CFHPs) have outstanding optical activity and CPL performance. The present contribution reports the first success in constructing emissive N*-LCs by doping CFHP into nematic liquid crystals (5CB, N-LCs). The helical assembly structures of N*-LCs effectively amplify the CPL signals of the CFHP. Owing to the high HTP of CFHP, the selective reflection band of N*-LC can be adjusted to fully cover its emission band. A nearly pure CPL with a dissymmetry factor (glum ) up to -1.87 is realized at 9 wt% doping concentration. Taking advantage of the selective reflection mechanism, multi-color CPL-active N*-LCs with high glum are fabricated via further adding achiral fluorophores. Also noticeably, circularly polarized room-temperature phosphorescence with glum up to -1.57 is achieved. Anti-counterfeiting application is demonstrated by exploiting multi-mode optical characteristics of the created N*-LCs. The established strategy for constructing emissive N*-LCs provides a platform for future exploring of CPL-active N*-LCs.

Liquid Crystal Assembly for Ultra-dissymmetric Circularly Polarized Luminescence and Beyond

Circularly polarized luminescence (CPL) is attracting much interest because it can carry extensive optical information. CPL shows left- or right-handedness and can be regarded as part of high-level visual perception to supply an extra dimension of information with regard to regular light. A key to meeting the needs for practical applications is to develop the emerging field of ultra-dissymmetric CPL. Chiral liquid crystal (LC) assemblies─otherwise referred to as cholesteric liquid crystals (CLCs)─are essentially organized helical superstructures with a highly ordered one-dimensional orientation, and distinctly superior to regular helical supramolecules. CLCs can achieve a perfect equilibrium of molecular short-range interaction and long-range orientational order, enabling molecule-scale chirality on a helical pitch and observable scale. LC assembly could be an ideal strategy for amplifying chirality, making it accessible to ultra-dissymmetric CPL. Herein, we focused on some basic but important issues regarding CPL: (i) How can CPL be created from chiral dyes? (ii) Is the chirality of luminescent dyes an essential factor for the generation of CPL? That is, can all chiral dyes emit CPL and vice versa? (iii) How can CPL be transferred within intermolecular systems, and what principles of CPL transmission should be followed? Given these queries and our work, in this Perspective we discuss the generation, transmission, and modulation of CPL with chiral LC assembly, aiming to design and build up novel chiroptical materials. Recent applications of CPL-active LC microstructures in three-dimensional displays, circularly polarized lasers, and asymmetric catalysis are also discussed.

Stepwise Amplification of Circularly Polarized Luminescence in Chiral Metal Cluster Ensembles

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

Air-tolerant upconverted circularly polarized luminescence enabled by confined space of chiral micelle

Circularly polarized luminescence (CPL) has been widely demonstrated that the circular polarization in excited state can be significantly amplified through the triplet-triplet annihilation-based upconversion (TTA-UC) luminescence process in various chiral nano-assemblies. However, constructing such an upconverted circularly polarized luminescence (UC-CPL) system in the aqueous phase remains a challenge. In this work, a kind of amphiphilic chiral cationic gemini surfactant is utilized to construct chiral spherical micelle in the aqueous phase, whose internal chiral cavity can provide a hydrophobic and deoxygenated environment for air-sensitive TTA-UC system. In addition, due to the co-assembly process between the emitters and chiral micelles, achiral emitters of upconversion pairs exhibit induced chiroptical properties. More importantly, the luminescence dissymmetry factor (g_lum ) can be amplified by one order of magnitude through TTA-UC process. This work provides an effective and useful strategy for realizing UC-CPL in aqueous phase.

Enhanced chiroptic properties of nanocomposites of achiral plasmonic nanoparticles decorated with chiral dye-loaded micelles

The development of circularly polarized luminescence (CPL)-active materials with both large luminescence dissymmetry factor (g_lum) and high emission efficiency continues to be a major challenge. Here, we present an approach to improve the overall CPL performance by integrating triplet-triplet annihilation-based photon upconversion (TTA-UC) with localized surface plasmon resonance. Dye-loaded chiral micelles possessing TTA-UC ability are designed and attached on the surface of achiral gold nanorods (AuNRs). The longitudinal and transversal resonance peaks of AuNRs overlap with the absorption and emission of dye-loaded chiral micelles, respectively. Typically, 43-fold amplification of g_lum value accompanied by 3-fold enhancement of upconversion are obtained simultaneously when Au@Ag nanorods are employed in the composites. More importantly, transient absorption spectra reveal a fast accumulation of spin-polarized triplet excitons in the composites. Therefore, the enhancement of chirality-induced spin polarization should be in charge of the amplification of g_lum value. Our design strategy suggests that combining plasmonic nanomaterials with chiral organic materials could aid in the development of chiroptical nanomaterials.

Chiroptical induction with prism[5]arene alkoxy-homologs

The complexation of prism[5]arenes with amino acid derivatives showed association constants of up to 10⁷ M^-1, significant CD with g_abs of up to 0.8 × 10^-2 and CPL with g_lum of 2 × 10^-3. The absolute configuration-CD signal correlation was established. The CD spectra varied significantly with the substituents on the prism[5]arenes.

Vortex Flow-controlled Circularly Polarized Luminescence of Achiral Pt(II) Complex Aggregates Assembled at the Air-Water Interface

Circularly polarized luminescence (CPL) has been researched for various applications by control of characteristics such as chirality and magnitude. Supramolecular chirality has been prepared by vortex motion as a mechanical stimulus; however, CPL has yet to be controlled precisely and reproducibly. In this work, the first precise control of CPL under vortex flow conditions at an air-water interface is reported. The supramolecular chirality of aggregates consisting of an achiral trans-bis(salicylaldiminato)Pt(II) complex bearing hexadecyl chains is induced and controlled with vortex flow at the air-water interface, whereas the complex naturally forms an achiral amorphous solid with non-chiroptical properties under non-vortex conditions. The CPL direction and magnitude (g_lum value) of the Pt(II) complex aggregates can be adjusted precisely according to the vortex conditions, including the rotatory direction and flow rate. Vortex-flow-induced emission enhancement is also observed upon an increase in the rate of the vortex flow.

Multicolor-tunable room-temperature afterglow and circularly polarized luminescence in chirality-induced coordination assemblies

Dynamic long-lived multicolor room temperature afterglow and circularly polarized luminescence (CPL) are promising for optoelectronic applications, but integration of these functions into a single-phase chiroptical material is still a difficult and meaningful challenge. Here, a nitrogen-doped benzimidazole molecule 1H-1,2,3-triazolopyridine (Trzpy) showing pure organic room-temperature phosphorescence (RTP) acted as a linker, and then, we propose a chirality-induced coordination assembly strategy to prepare homochiral crystal materials. Two homochiral coordination polymers DCF-10 and LCF-10 not only exhibit multicolor-tunable RTP, the color changed from green to orange under various excitation wavelengths, but also show remarkable excitation-dependent circularly polarized luminescence (CPL), and the dissymmetry factors of CPL in DCF-10 and LCF-10 are 1.8 × 10^-3 and 2.4 × 10^-3, respectively. Experimental and theoretical studies demonstrated that molecular atmospheres with different aggregation degrees give rise to multiple emission centers for the generation of multicolor-tunable emission. The multicolor-tunable photophysical properties endowed LCF-10 with a huge advantage for multi-level anti-counterfeiting. This work opens up new perspectives for the development and application of color-tunable RTP and CPL.

Stereomutation and chiroptical bias in the kinetically controlled supramolecular polymerization of cyano-luminogens

The synthesis of two pairs of enantiomeric cyano-luminogens 1 and 2, in which the central chromophore is a p-phenylene or a 2,5-dithienylbenzene moiety, respectively, is described and their supramolecular polymerization under kinetic and thermodynamic control investigated. Compounds 1 and 2 form supramolecular polymers by quadruple H-bonding arrays between the amide groups and the π-stacking of the central aromatic moieties. In addition, the peripheral benzamide units are able to form intramolecularly H-bonded pseudocycles that behave as metastable monomer M* thus affording kinetically and thermodynamically controlled aggregated species AggI and AggII. The chiroptical and emissive features of compounds 1 and 2 strongly depend on the aggregation state and the nature of the central aromatic unit. Compounds 1 exhibit a bisignated dichroic response of different intensity but with similar sign for both AggI1 and AggII1 species, which suggests the formation of helical aggregates. In fact, these helical supramolecular polymers can be visualized by AFM imaging. Furthermore, both AggI and AggII species formed by the self-assembly of compounds 1 show CPL (circularly polarized light) activity of opposite sign depending on the aggregation state. Thienyl-derivatives 2 display dissimilar chiroptical, morphological and emissive characteristics for the corresponding kinetically and thermodynamically controlled aggregated species AggI and AggII in comparison to those registered for compounds 1. Thus, a stereomutation phenomenon is observed in the AggI2 → AggII2 conversion. In addition, AggI2 is arranged into nanoparticles that evolve to helical aggregates to afford AggII2. The dissimilar chiroptical and morphological features of AggI2 and AggII2 are also appreciated in the emissive properties. Thus, whilst AggI2 experiences a clear AIE (aggregation induced emission) process and CPL activity, the thermodynamically controlled AggII2 undergoes an ACQ (aggregation caused quenching) process in which the CPL activity is cancelled.

The preparation and properties of circularly polarized luminescent liquid crystal physical gels with self-supporting performance

In recent years, great progress has been made in the preparation methods and performance regulation of host-guest doped CPL liquid crystal materials. However, there still exist some basic problems to be solved, such as complex packaging and unstable CPL properties. With the consideration of the above problems, in this study, we introduced gelators into the host-guest doped CPL liquid crystal materials to prepare CPL liquid crystal physical gels. The gelators can be assembled to form a nanofiber physical gel network, which limits the movement of the liquid crystals and enhances the stability of the CPL properties. Meanwhile, liquid crystal physical gels show self-supporting ability and the gel-sol phase transition temperature can reach 136 °C. The amplification of the g_lum value is achieved by self-assembly of chiral liquid crystals, and the g_lum value can reach -0.31. The phase structure changes with electric field and temperature, and the CPL properties can be regulated by changing the temperature and electric field. With the increasing applied voltage or the temperature, the g_lum value decreases. Therefore, we have successfully prepared a new type of CPL liquid crystal physical gels with self-supporting performance, stimulus response performance and large g_lum values.

Selective synthesis and (chir)optical properties of binaphthyl-based chiral carbon macrocycles

Herein, we report the selective synthesis, characterization, and photophysical properties of two novel chiral carbon macrocycles. Non-planar (S)-2,2'-bis(methoxymethoxy)-1,1'-binaphthalene was introduced into the scaffold of oligo-paraphenylenes to achieve the chirality in these macrocycles. Their photophysical properties were investigated by steady-state and time-resolved spectroscopies, as well as circular dichroism and circularly polarized luminescence spectroscopies. We demonstrate that the emission maxima of the chiral macrocycles are redshifted compared to chiral binaphthyl units and that macrocycles show chiroptical properties (|g_lum| > 1.0 × 10^-3).

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.

Complex-as-Ligand Strategy as a Tool for the Design of a Binuclear Nonsymmetrical Chromium(III) Assembly: Near-Infrared Double Emission and Intramolecular Energy Transfer

The chromium(III) polypyridyl complexes are appealing for their long-lived near-infrared (NIR) emission reaching the millisecond range and for the strong circularly polarized luminescence of their isolated enantiomers. However, harnessing those properties in functional polynuclear Cr^III devices remains mainly inaccessible because of the lack of synthetic methods for their design and functionalization. Even the preparation and investigation of most basic nonsymmetrical Cr^III dyads exhibiting directional intramolecular intermetallic energy transfer remain unexplored. Taking advantage of the inertness of heteroleptic chromium(III) polypyridyl building blocks, we herein adapt the "complex-as-ligand" strategy, largely used with precious 4d and 5d metals, for the preparation of a binuclear nonsymmetrical Cr^III complex (3d metal). The resulting [(phen)₂Cr(L)Cr(tpy)]⁶⁺ dyad shows dual long-lived NIR emission and a directional intermetallic energy transfer that is controlled by the specific arrangements of the different coordination spheres. This strategy opens a route for building predetermined polynuclear assemblies with this earth-abundant metal.

Excellent upconversion luminescence and temperature sensing performance of CdMoO4:Er3+,Yb3+ phosphors

In this paper, Er³⁺/Yb³⁺ co-doped CdMoO₄ phosphors were prepared by a traditional high temperature solid state reaction method. Based on the 3D network structure of the CdMoO₄ host and the efficient Er³⁺/Yb³⁺ upconversion luminescence combinations, excellent green emission properties were observed when the prepared sample is irradiated with a laser at about 980 nm. For optical temperature sensors based on the fluorescence intensity ratio (FIR), the prepared phosphors have excellent sensitivity to temperature in the range of 293 to 473 K. With increasing environmental temperatures, the absolute sensitivity of the CdMoO₄:0.02Er³⁺,0.08Yb³⁺ sample reached a maximum at about 473 K (S_a = 1.388% K^-1). The calculated relative sensitivity of the optical temperature sensor was S_r = 1.631% K^-1 at 293 K. This is due to the sensitive thermally coupled energy levels (TCLs) of the Er³⁺ ions (²H_11/2 and ⁴S_3/2) in the CdMoO₄ structure. Therefore, it is shown that the prepared CdMoO₄:0.02Er³⁺,0.08Yb³⁺ phosphor has excellent applications in non-contact optical temperature measurement.

Optically Coupled PtOEP and DPA Molecules Encapsulated into PLGA-Nanoparticles for Cancer Bioimaging

Triplet-triplet annihilation upconversion (TTA-UC) nanoparticles (NPs) have emerged as imaging probes and therapeutic probes in recent years due to their excellent optical properties. In contrast to lanthanide ion-doped inorganic materials, highly efficient TTA-UC can be generated by low excitation power density, which makes it suitable for clinical applications. In the present study, we used biodegradable poly(lactic-co-glycolic acid) (PLGA)-NPs as a delivery vehicle for TTA-UC based on the heavy metal porphyrin Platinum(II) octaethylporphyrin (PtOEP) and the polycyclic aromatic hydrocarbon 9,10-diphenylanthracene (DPA) as a photosensitizer/emitter pair. TTA-UC-PLGA-NPs were successfully synthesized according to an oil-in-water emulsion and solvent evaporation method. After physicochemical characterization, UC-efficacy of TTA-UC-PLGA-NPs was assessed in vitro and ex vivo. TTA-UC could be detected in the tumour area 96 h after in vivo administration of TTA-UC-PLGA-NPs, confirming the integrity and suitability of PLGA-NPs as a TTA-UC in vivo delivery system. Thus, this study provides proof-of-concept that the advantageous properties of PLGA can be combined with the unique optical properties of TTA-UC for the development of advanced nanocarriers for simultaneous in vivo molecular imaging and drug delivery.

Manipulating the Assembly of Au Nanoclusters for Luminescence Enhancement and Circularly Polarized Luminescence

Au nanocluster (AuNCs)-based luminescent functional materials have attracted the interest of researchers owing to their small size, tractable surface modification, phosphorescence lifetime and biocompatibility. However, the poor luminescence quantum yield (QY) of AuNCs limits their practical applications. Herein, we synthesized a type of AuNCs modified by 4,6-diamino-2-mercaptopyrimidine hydrate (DPT-AuNCs). Furthermore, organic acids, i.e., citric acid (CA) and tartaric acid (TA), were chosen for co-assembly with DPT-AuNCs to produce AuNCs-based luminescent materials with enhanced emission. Firstly, it was found that CA could significantly enhance the emission of DPT-AuNCs with the formation of red emission nanofibers (QY = 17.31%), which showed a potential for usage in I- detection. The n···π/π···π interaction between the CA and the DPT ligand was proposed as crucial for the emission. Moreover, chiral TA could not only improve the emission of DPT-AuNCs, but could also transfer its chirality to DPT-AuNCs and induce the formation of circularly polarized luminescence (CPL)-active nanofibers. It was demonstrated that the CPL signal could increase 4.6-fold in a ternary CA/TA/DPT-AuNCs co-assembly system. This work provides a convenient way to build AuNCs-based luminescent materials as probes, and opens a new avenue for building CPL-active materials by achiral NCs through a co-assembly strategy.

Phthalocyanine-Triggered Helical Dipeptide Nanotubes with Intense Circularly Polarized Luminescence

Nanotubes with circularly polarized luminescence (CPL) are attracting much attention due to many potential applications, such as chiroptical materials, displays, and sensing. However, it remains a challenge to change the assemblies of ordinarily molecular building blocks into CPL supramolecular nanotubes. Herein, the regulation of quite common dipeptide (Fmoc-FF) assemblies into unprecedented helical nanotubes exhibiting intense CPL is reported by simply doping a few phthalocyanine (octakis(carboxyl)phthalocyaninato zinc complex (Pc)) molecules. Interestingly, altering the Fmoc-FF/Pc molar ratios over a wide range cannot change the nanotubes structures according to transmission electron microscopy (TEM) and atomic force microscope (AFM) measurements. Although molecular dynamics simulations suggest that the noncovalent interactions between Fmoc-FF and Pc are quite weak, few Pc molecules can still change the secondary structures of a large number of Fmoc-FF assemblies, which hierarchically form helical supramolecular nanotubes with long-range ordered molecular packing, leading to intense CPL signals with large luminescence dissymmetry factor (g_lum  = 0.04). Consequently, the chiral reorganization of Fmoc-FF assemblies is dependent on the coassembly between Pc molecule and Fmoc-FF supramolecular architectures. These results open the possibility for the fine-tuning of helix and supramolecular nanotubes with CPL properties by using a small number of cofactors.

Ultraviolet Light Detectable Circularly Polarized Room Temperature Phosphorescence in Chiral Naphthalimide Self-Assemblies

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

Chiral macrocycle-induced circularly polarized luminescence of a twisted intramolecular charge transfer dye

The host-guest binding between a chiral macrocycle and an achiral dye could suppress the twisted intramolecular charge transfer (TICT) process, leading to enhanced emission and bright circularly polarized luminescence (CPL) from the originally achiral TICT-dye.

Luminescent Chiral Exciplexes with Sky-Blue and Green Circularly Polarized-Thermally Activated Delayed Fluorescence

Luminescent exciplexes based on a chiral electron donor and achiral acceptors are reported as a new approach to design circularly polarized (CP) and thermally activated delayed fluorescence (TADF) emitters. This strategy results in rather high CP luminescence (CPL) values with g_lum up to 7×10^-3 , one order of magnitude higher in comparison to the CPL signal recorded for the chiral donor alone (g_lum ∼7×10^-4 ). This increase occurs concomitantly with a CPL sign inversion, as a result of the strong charge-transfer emission character, as experimentally and theoretically rationalized by using a covalent chiral donor-acceptor model. Interestingly, blue, green-yellow and red chiral luminescent exciplexes can be obtained by modifying with the electron accepting character of the achiral unit while keeping the same chiral donor unit. These results bring new (inter)molecular guidelines to obtain simply and efficiently multi-color CP-TADF emitters.

Large π-Extended and Curved Carbon Nanorings as Carbon Nanotube Segments

ConspectusDesigning and synthesizing topologically unique molecules is a long-term challenge for synthetic chemists. Classical polycyclic aromatic hydrocarbons (PAHs) are a large group of π-conjugated planar organic compounds with rich photophysical and electronic properties, while nonplanar/curved PAHs have different molecular orbital arrangements and demonstrate unique properties. The chemistry of curved aromatic molecules has been of significant interest to explore the relationship between π conjugation and molecular geometry, which offers an attractive combination of fundamental problems, potential applications, and aesthetic appeal. Remarkable advances have been made in the last few decades during the discovery of novel curved aromatic molecules, including corannulenes, fullerenes, and carbon nanotubes (CNTs). Especially, there has been increasing interest in making single-chirality CNTs and their curved molecular components (known as finite segments of CNTs) with a fixed geometry. The most representative examples of such organic molecules are cycloparaphenylenes (CPPs) and related carbon nanorings, which possess cylindrical topologies and nanoscale conjugated segments similar to CNTs. CPPs, as the shortest cross-section and the simplest structure of armchair CNTs, have been synthetically accessible since 2008. Recent years have witnessed breakthroughs and rapid development in the synthesis of CPP-based nanorings as well as their derived molecules. In these molecules, the distortion from aromatic planarity can induce radially oriented π systems and further affect their electronic, optical, self-assembly, and charge-transport characteristics. These unique and interesting carbon nanorings are potentially useful in a variety of optoelectronic and biomedical materials. It is well-known that extension of the π-conjugated system facilitates the delocalization of π electrons and the redistribution of electronic clouds, leading to rich diversification of physical properties in the fields of electronics, optics, and supramolecular chemistry. Therefore, the precise design and controllable synthesis of carbon nanorings with large π conjugation will promote important advances in synthetic chemistry. To date, a number of π-extended carbon nanorings have been reported, and they exhibit novel physicochemical properties resulting from their fascinating topologies and structures. However, challenges still remain in the synthesis of π-extended carbon nanorings and their structural analogues and exploration of their unique properties.In this Account, we give a brief overview of our efforts to synthesize large π-extended carbon nanorings using different strategies and explore their novel applications. In 2013 we started our research on the synthesis of carbon nanorings with large π-conjugated structures. This research project has led to (i) the successful preparation of a series of carbon nanorings with inserted PAHs, especially with various nanographenes inserted, such as hexa-peri-hexabenzocoronene; (ii) the design and synthesis of a series of carbon nanorings consisting solely of PAHs; and (iii) the initial synthesis of π-extended carbon-nanoring-based polymers as the long polymeric segments of CNTs, in which macrocyclic CPPs as the basic repeating blocks were covalently coupled together. Herein we describe in detail how these challenging π-extended carbon nanorings were synthesized, and their interesting physical properties are discussed.

Ring-Expansion Strategy for α-Aryl Azahelicene Construction: Building Blocks for Optoelectronic Materials

An acid-mediated rapid synthesis of α-aryl azahelicenes via C-C bond cleavage of helical 9H-fluoren-9-ols is reported. The newly introduced aryl ring and pyridine moieties provide an excellent opportunity to further tune the properties of azahelicences: i.e., photoluminescence. The novel α-aryl azahelicenes showcase high circularly polarized luminescence (CPL) efficiencies (4.5 × 10^-3) as well as CPL brightness (B_CPL), reaching 7.39 M^-1 cm^-1, which indicates a potential application as chiral emitters.