Circularly Polarized Luminescence Properties Research Articles

Circularly polarized luminescence in chiral nematic liquid crystals based on photochromic molecules

Circularly polarized luminescence (CPL) has emerged as a focal point in luminescent materials research, reflecting a growing field of study. Responding to the demand for practical applications across diverse sectors, there is a critical need for CPL materials with high luminescence dissymmetry factors (g lum) and adjustable optical performance, driving the development of novel materials and methodological approaches. Chiral nematic liquid crystals (N*-LCs) have attracted significant attention as promising candidates for producing high-performance CPL materials due to their ability to exhibit enhanced g lum and modulate circularly polarized light. This review comprehensively presents the stimuli-responsive CPL properties, utilizing N*-LCs as chiral templates doped with various photochromic compounds, particularly azobenzene, spiropyran (SP), diarylethene and overcrowded alkene. By elucidating the dynamic interplay between molecular structure, supramolecular organization, and optical response, it offers a profound understanding of the stimuli-responsive CPL behaviors. Additionally, the review also explores the multifaceted applications of photochromic N*-LCs materials, spanning advanced display technologies, optical data storage, and beyond. By examining diverse avenues for leveraging their unique optical properties, it highlights their pivotal role in driving innovation across photonic applications, facilitating transformative advancements in the field.

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

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

Reversible Local Protonation-Deprotonation: Tuning Stimuli-Responsive Circularly Polarized Luminescence in Chiral Hybrid Zinc Halides for Anti-Counterfeiting and Encryption.

Precise control over the organic composition is crucial for tailoring the distinctive structures and properties of hybrid metal halides. However, this approach is seldom utilized to develop materials that exhibit stimuli-responsive circularly polarized luminescence (CPL). Herein, we present the synthesis and characterization of enantiomeric hybrid zinc bromides: biprotonated ((R/S)-C12H16N2)ZnBr4 ((R/S-LH2)ZnBr4) and monoprotonated ((R/S)-C12H15N2)2ZnBr4 ((R/S-LH1)2ZnBr4), derived from the chiral organic amine (R/S)-2,3,4,9-Tetrahydro-1H-carbazol-3-amine ((R/S)-C12H14N2). These compounds showcase luminescent properties; the zero-dimensional biprotonated form emits green light at 505 nm, while the monoprotonated form, with a pseudo-layered structure, displays red luminescence at 599 and 649 nm. Remarkably, the reversible local protonation-deprotonation behavior of the organic cations allows for exposure to polar solvents and heating to induce reversible structural and luminescent transformations between the two forms. Theoretical calculations reveal that the lower energy barrier associated with the deprotonation process within the pyrrole ring is responsible for the local protonation-deprotonation behavior observed. These enantiomorphic hybrid zinc bromides also exhibit switchable circular dichroism (CD) and CPL properties. Furthermore, their chloride counterparts were successfully obtained by adjusting the halogen ions. Importantly, the unique stimuli-responsive CPL characteristics position these hybrid zinc halides as promising candidates for applications in information storage, anti-counterfeiting, and information encryption.

Reversible Local Protonation‐Deprotonation: Tuning Stimuli‐Responsive Circularly Polarized Luminescence in Chiral Hybrid Zinc Halides for Anti‐Counterfeiting and Encryption

AbstractPrecise control over the organic composition is crucial for tailoring the distinctive structures and properties of hybrid metal halides. However, this approach is seldom utilized to develop materials that exhibit stimuli‐responsive circularly polarized luminescence (CPL). Herein, we present the synthesis and characterization of enantiomeric hybrid zinc bromides: biprotonated ((R/S)‐C12H16N2)ZnBr4 ((R/S‐LH2)ZnBr4) and monoprotonated ((R/S)‐C12H15N2)2ZnBr4 ((R/S‐LH1)2ZnBr4), derived from the chiral organic amine (R/S)‐2,3,4,9‐Tetrahydro‐1H‐carbazol‐3‐amine ((R/S)‐C12H14N2). These compounds showcase luminescent properties; the zero‐dimensional biprotonated form emits green light at 505 nm, while the monoprotonated form, with a pseudo‐layered structure, displays red luminescence at 599 and 649 nm. Remarkably, the reversible local protonation‐deprotonation behavior of the organic cations allows for exposure to polar solvents and heating to induce reversible structural and luminescent transformations between the two forms. Theoretical calculations reveal that the lower energy barrier associated with the deprotonation process within the pyrrole ring is responsible for the local protonation‐deprotonation behavior observed. These enantiomorphic hybrid zinc bromides also exhibit switchable circular dichroism (CD) and CPL properties. Furthermore, their chloride counterparts were successfully obtained by adjusting the halogen ions. Importantly, the unique stimuli‐responsive CPL characteristics position these hybrid zinc halides as promising candidates for applications in information storage, anti‐counterfeiting, and information encryption.

Room-Temperature Liquid Crystalline Tetraphenylethylene-Surfactant Complex with Chiral Supramolecular Structure and Tunable Circularly Polarized Luminescence.

A novel room-temperature liquid crystal of tetraphenylethylene derivative (TPE-DHAB) was synthesized using an ionic self-assembly strategy. The TPE-DHAB complex exhibits typical aggregation-induced emission properties and a unique helical supramolecular structure. Moreover, the generation and handedness inversion of circularly polarized luminescence (CPL) can be achieved through further chiral solvation, providing a facile approach to fabricate room-temperature liquid crystalline materials with controllable supramolecular structures and tunable CPL properties through a synergistic strategy of ionic self-assembly and chiral solvation process.

High‐Efficiency Circularly Polarized Luminescence Regulation of a Dye‐Doped Polymer Film by Acid/Aggregation

AbstractSmart materials with circularly polarized luminescence (CPL) tunable ability show great potential for advanced information storage and encryption. While an effective integration of high photoluminescence quantum yield (PLQY) and facile regulation of CPL property in thin films are of great significance, it is challenging due to the scarcity of suitable materials and complexity of systems. Herein, a novel acid‐responsive CPL tunable molecule is designed by combining an aggregation‐induced emission (AIE) component (TPE), an acid‐responsive luminophore (Rhodol), and a chiral aniline. Benefitting by the “AIE” effect of TPE and acid‐sensitive nature of Rhodol, the acidified molecule (S‐Rhodol‐TPE) exhibits a high PLQY even when doped in the polymer substrate at high concentrations. In addition, due to the fluorescence resonance energy transfer (FRET) process between TPE and Rhodol, the emission color of S‐Rhodol‐TPE can be easily regulated by the doped ratio and acidified degree of S‐Rhodol‐TPE in the polymer film. This work exhibits a unique approach to achieving smart CPL‐tunable films with high PLQYs and multiple emission color‐regulation properties, which can undoubtedly facilitate the progress of CPL tunable materials.

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

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

Substituent effect induced circularly polarized luminescence enhancement of Eu(III) enantiomers

Circularly polarized luminescence (CPL) has received much attention in optical displays, information storage, and biological probes. Designing effective strategy to improve the CPL activities is significant for complex materials. Structural modification is a rational way which is seldom reported. In this work, three chiral binuclear Eu(III) complexes coordinated with different chiral Schiff base ligands were designed and synthesized. CPL performances of these Eu(III) complexes were substantially improved by polarity of substituents at the chiral carbon sites of the ligands, leading to a five-fold increase in the luminescence dissymmetry factor (glum). Additionally, three complexes exhibited similar luminescence properties with the characteristic peaks of Eu(III) ion, which can be rapidly quenched by Co(II) ion, allowing their further applications in anti-counterfeiting and sensors. Therefore, this work not only uncovers the relationship between the substituents of chiral ligand and the corresponding CPL properties of Eu(III) complexes to some extent, but also creates opportunities for design and synthesis of Eu(III) complexes with excellent CPL activity.

Tetraphenylethylene-based conjugated polymers with valine-containing side chains: Aggregation-induced emission, helical self-assembly, complexation-induced circularly polarized luminescence

Realizing high circularly polarized luminescence (CPL) in polymer system is an important but challenging task. Herein, we provide a strategy for designing conjugated polymers with high CPL performance upon the complexation with mandelic acids. Two tetraphenylethylene (TPE)-based conjugated polymers, l-P1 and d-P1, were synthesized by Sonogashira polycoupling reactions between the TPE-containing diethynyl monomer and dibromo aryl monomers carrying valine methyl ester groups. Both the polymers showed aggregation-induced emission (AIE) properties and the capabilities to self-assemble into regular helical nanostructures on nanoscale and fluorescent microfibers on microscale. They exhibited weak circular dichroism (CD) signals; upon the complexation with R/S-mandelic acids, their CD absorption and fluorescence emission can be efficiently enhanced. The composite films of l/d-P1 and R/S-mandelic acids exhibited excellent complexation-induced CPL properties with the absolute luminescence dissymmetric factor (glum) up to 0.01 and the fluorescence quantum yield up to 26.8%; the glum values showed little dependence on their emission wavelength. Various types of carboxyl acids have been screened and only mandelic acids show significantly chiroptical induction. The specific interaction between mandelic acids and l/d-P1 also makes the latter promising candidates for the enantioselective recognition of chiral organic molecules.

Two Different Chiral Groups Based Thermally Activated Delayed Fluorescence Materials for Circularly Polarized OLEDs.

Circularly polarized organic light-emitting diodes (CP-OLEDs) hold significant promise for applications in 3D displays due to the ability to generate circularly polarized luminescence (CPL) directly. In this study, two pairs of circularly polarized thermally activated delayed fluorescence (CP-TADF) enantiomers, named RR/SS-ONCN and RS/SR-ONCN, were synthesized by integrating two distinct chiral groups into the dicyanobenzene unit. The RR/SS-ONCN and RS/SR-ONCN enantiomers show CPL properties with dissymmetry photoluminescence factors (|gPL|) of 1.3×10-3 and 2.0×10-3 in doped films, respectively. Notably, RR/SS-ONCN exhibit higher |gPL| values than that of RS/SR-ONCN, especially in doped films, indicating that when the configurations of the two chiral groups are identical, the |gPL| value of the CP-TADF materials can be enhanced, demonstrating a certain stacking effect. Moreover, the corresponding CP-OLEDs demonstrate good performances, achieving maximum external quantum efficiencies of up to 21.9 % and notable CP electroluminescence with |gEL| factors of up to 1.0×10-3.

Recent Progress in Circularly Polarized Luminescent Materials Based on Cyclodextrins.

Circularly polarized luminescence (CPL) materials have been widely used in the fields of bioimaging, optoelectronic devices, and optical communications. The supramolecular interaction, involving harnessing non-covalent interactions between host and guest molecules to control their arrangements and assemblies, represents an advanced approach for facilitating the development of CPL materials and finely constructing and tuning the desired CPL properties. Cyclodextrins (CDs) are cyclic natural polysaccharides, which have also been ubiquitous in various fields such as molecular recognition, drug encapsulation, and catalyst separation. By adjusting the interactions between CDs and guest molecules precisely, composite materials with CPL properties can be facilely generated. This review aims to outline the design strategies and performance of CD-based CPL materials comprehensively and provides a detailed illustration of the interactions between host and guest molecules.

Switching of Circularly Polarized Luminescence via Dynamic Axial Chirality Control of Chiral Bis(Boron Difluoride) Complexes with Salen Ligands

AbstractThe intensity and handedness of circularly polarized luminescence (CPL) were successfully controlled by dynamic molecular motion in solutions. Bis(boron difluoride) complexes with chiral salen ligands were synthesized and their photophysical properties were investigated. Although these complexes showed rapid molecular rotation about the C−N bond axis in solution at room temperature, two conformers assigned as atropisomers were observed in the NMR spectra at low temperature. Furthermore, the equilibrium of these atropisomers was found to change depending on the external environment, such as the solvent and temperature, allowing precise control of the intensity and handedness of CPL without luminescence color shifts. Theoretical calculations based on density functional theory (DFT) revealed that intramolecular chiral exciton coupling is the key to changes in CPL properties.

Circularly Polarized Electroluminescence from Intrinsically Axial Chiral Materials Based on Bidibenzo[b,d]furan/bidibenzo[b,d]thiophene

AbstractHerein, by connecting chiral bidibenzo[b,d]furan/bidibenzo[b,d]thiophene and multi‐resonance thermally activated delayed fluorescence (MR‐TADF) units, two pairs of intrinsically axial chiral MR‐TADF materials (R/S‐BDBF‐BNO and R/S‐BDBT‐BNO) realize mirror‐symmetric circularly polarized luminescence (CPL) and narrowband emission. The chiral moieties effectively engage in frontier molecular orbital distributions through the establishment of covalent bonds with boron atoms. The proportions of (1,1′‐bidibenzo[b,d]furan)‐2,2′‐diol in the highest occupied and lowest unoccupied natural transition orbitals (HONTO/LUNTO) are 25.3% and 64.7%, respectively. In addition, BDBT‐BNO processes a dual‐channel transition mode, thus the (1,1′‐bidibenzo[b,d]thiophene)‐2,2′‐diol constitutes 22.8%, 24.3% and 54.0%, 46.9% of the distributions of HONTO, HONTO‐1 and LUNTO, LUNTO+1, respectively. The high proportions endow R/S‐BDBF‐BNO and R/S‐BDBT‐BNO with good CPL properties with dissymmetry factors (|gPL|) of 1.7/1.8 × 10−3. Correspondingly, the circularly polarized organic light‐emitting diodes based on the enantiomers exhibit mirror symmetrical circularly polarized electroluminescence with |gEL| factors of 1.5/1.6 × 10−3. Furthermore, the introduction of sulphur atoms enables BDBT‐BNO to have a high maximum external quantum efficiency of 35.7% in device.

A Multiple Circularly Polarized Luminescence Regulation Platform Driven by Acid, Base, and Primary Amines

AbstractFunctional materials that exhibit circularly polarized luminescence (CPL) have shown immense potential in applications such as 3D optical displays and advanced information encryption. However, facile and efficient regulation of the multiple emission properties in chiral systems has remained a challenge due to the scarcity of suitable materials and the complexity of the systems. Herein, a multiple CPL regulation platform is fabricated by the helical co‐assembly of an aldehyde‐functionalized fluorane dye (Rhodol‐CHO, 6′‐(diethylamino)‐3′‐hydroxy‐3‐oxo‐3H‐spiro[isobenzofuran‐1,9′‐xanthene]‐4′‐carbaldehyde) and chiral liquid crystals, which can efficiently combine multiple stimuli‐responsive characteristics and high optical activity. By introducing acid, base, and compounds containing primary amino (─NH2) groups, the CPL property of the system can be easily modified. The obtained CPL systems exhibit apparent asymmetry, with glum values reaching 0.54–0.75). Further, these CPL modules are successfully applied in multi‐mode information encryption, highlighting their practical utility. Therefore, this study presents a novel strategy for developing materials with diverse CPL behaviors based on a simple‐designed platform, advancing further applications of CPL materials.

Recent Advances of Chiral Isolated and Small Organic Molecules: Structure and Properties for Circularly Polarized Luminescence.

This paper explores recent advancements in the field of circularly polarized luminescence (CPL) exhibited by small and isolated organic molecules. The development and application of small CPL molecule are systematically reviewed through eight different chiral skeleton sections. Investigating the intricate interplay between molecular structure and CPL properties, the paper aims at providing and enlighting novel strategies for CPL-based applications.

Construction of Circular Polarized Luminescence Molecules for Intense Near Infrared OLEDs

AbstractThe exploration of organic near‐infrared (NIR) luminescence, along with circularly polarized luminescence (CPL), is of vital importance due to its significance in medical and optoelectronic applications. Integrating a chiral unit into a D–A molecular structure in this research realized emission peaks at 744 nm, exhibiting a dissymmetric factor of −1.67 × 10−3. The introduced chiral TPA derivative not only imparts aggregation‐induced emission properties and CPL capabilities but also induces a redshift in the emission spectrum. Consequently, the fabricated NIR organic light‐emitting devices (OLEDs), achieve maximum electroluminescent peaks at 748 nm in nondoped devices with the external quantum efficiency of 13.7% in doped devices. This pioneering research provides inspiration for the design of NIR molecules possessing CPL properties in the future, particularly in promoting the application of intense NIR‐OLEDs.

Color-tunable circularly polarized luminescence from liquid crystalline polymer networks

Chiroptical materials with circularly polarized luminescence (CPL) activities have attracted increasing interest because of their promising applications in optoelectronics, biosensing and imaging. Nevertheless, the construction of CPL-active materials with large luminescence dissymmetry (glum) factors and high emission efficiency is still challenging. Herein, a series of liquid crystalline polymer network films have been prepared by photopolymerization of cholesteric liquid-crystalline mixtures doped with aggregation-induced emission-active luminogens, TPE-TA and BDABFN. Through adjustment of the mass ratio of the two luminogens, the resultant films exhibit multicolour CPL from blue to red to white with absolute glum values up to 0.71 and fluorescence quantum yields up to 44 %. This work provides a strategy for fabricating polymeric film materials with color-tunable CPL properties and high fluorescence efficiency.

Synthesis and Chiroptical Properties of Radially Extended Carbazole with Chiral [2.2]Paracyclophane Core

Abstract[2.2]Paracyclophanes ([2.2]PCs) with substituents at specific positions possesses planar chirality and stands as a promising building unit for the development of chiroptical materials associated with polarized light. However, one of the easily accessible starting materials, bromo‐substituted [2.2]PC, shows low reactivity, and effective methods for π‐extension of planar chiral [2.2]PC are limited. Herein, an effective π‐extension method has established for chiral [2.2]PC with four substitutions from 4,7,12,15‐tetrabromo[2.2]PC. This has led to tetrakis(trimethylsilylphenyl)‐[2.2]PC that serves as a versatile building resource for radial‐type chiral π‐conjugated compounds with a [2.2]PC core. In this study, synthesizing compounds are further succeeded with the introduction of carbazole (Cbz4‐[2.2]PC and tBuCbz4‐[2.2]PC) and investigated their chiroptical properties and chiral induction ability in achiral π‐conjugated polymers. A thin film of [Poly[9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,7‐diyl)]] (F8BT) with 3wt% Cbz4‐[2.2]PC prepared by spin‐coating exhibits circularly polarized luminescence (CPL) properties with a high dissymmetry factor (|glum| = 0.01), which is much higher than that of Cbz4‐[2.2]PC in CH2Cl2 solution. By contrast, the doped film of F8BT with 3wt% tBuCbz4‐[2.2]PC exhibited only weak CPL properties. In addition, these chiral compounds show facile redox properties owing to the presence of carbazole units. Furthermore, Cbz4‐[2.2]PC undergoes electropolymerization to produce an insoluble thin film on the electrode.

Modulation of luminescence properties of circularly polarized thermally activated delayed fluorescence molecules with axial chirality by donor engineering.

Multifunctional thermally activated delayed fluorescence (TADF) materials are currently a trending research subject for luminescence layer materials of organic light-emitting diodes (OLEDs). Among these, circularly polarized thermally activated delayed fluorescence (CP-TADF) materials have the advantage of being able to directly achieve highly efficient circularly polarized luminescence (CPL). The simultaneous integration of outstanding luminescence efficiency and excellent luminescence asymmetry factor (glum) is a major constraint for the development of CP-TADF materials. Therefore, on the basis of first-principles calculations in conjunction with the thermal vibration correlation function (TVCF) method, we study CP-TADF molecules with different donors to explore the feasibility of using the donor substitution strategy for optimizing the CPL and TADF properties. The results indicate that molecules with the phenothiazine (PTZ) unit as the donor possess small energy difference, a great spin-orbit coupling constant and a rapid reverse intersystem crossing rate, which endow them with remarkable TADF features. Meanwhile, compared with the reported molecules, the three designed molecules exhibit better CPL properties with higher glum values. Effective molecular design strategies by donor engineering to modulate the CPL and TADF properties are theoretically proposed. Our findings reveal the relationship between molecular structures and luminescence properties of CP-TADF molecules and further provide theoretical design strategies for optimizing the CPL and TADF properties.

Construction of an Au12Cd2 nanocluster with circularly polarized luminescence by a metal- and ligand-exchange strategy.

Excellent luminescence properties and unique chiral structures enable nanoclusters to be a novel class of circularly polarized luminescence (CPL) materials, and their precise structures facilitate the clarification of structure-activity relationships. However, efficiently preparing nanoclusters with CPL properties is still a great challenge. In this work, the luminescent properties as well as the molecular symmetry were simultaneously manipulated to transform the centrosymmetric Au14Cd1 into a chiral Au12Cd2 nanocluster, which has CPL properties. In detail, Cd doping and chiral-ligand exchange were performed simultaneously on the Au14Cd1 nanocluster to realize its photoluminescence enhancement and chiral-framework construction by increasing the alloying degree which is defined as deep-alloying and chiral ligand induction at the same time, resulting in the formation of an Au12Cd2 nanocluster with CPL properties. Further investigations revealed an increased alloying degree in the structure-maintained M6 kernel of Au12Cd2, which results in a 15-fold enhancement in quantum yield.