Circularly Polarized Luminescence Activity Research Articles

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

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

Loading Dyes into Chiral Cd/Zn‐Metal–Organic Frameworks for Efficient Full‐Color Circularly Polarized Luminescence

AbstractHost‐guest chemistry of chiral metal‐organic frameworks (MOFs) has endowed them with circularly polarized luminescence (CPL), it is still limited for MOFs to systematically tune full‐color CPL emissions and sizes. This work directionally assembles the chiral ligands, metal sites and organic dyes to prepare a series of crystalline enantiomeric D/L‐Cd/Zn‐n MOFs (n=1~5, representing the adding amount of dyes), where D/L‐Cd/Zn with the formula of Cd2(D/L–Cam)2(TPyPE) and Zn2(D/L–Cam)2(TPyPE) (D/L‐Cam=D/L‐camphoric acid, TPyPE=4,4’,4’’,4’’’‐(1,2‐henediidenetetra‐4,1‐phenylene)tetrakis[pyridine]) were used as the chiral platforms. The framework‐dye‐enabled emission and through‐space chirality transfer facilitate D/L‐Cd/Zn‐n bright full‐color CPL activity. The ideal yellow CPL of D‐Cd‐5 and D‐Zn‐4, with |glum| as 4.9 × 10−3 and 1.3×10−3 and relatively high photoluminescence quantum yield of 40.79 % and 45.40 %, are further assembled into a white CPL light‐emitting diode. The crystal sizes of D/L‐Cd/Zn‐n were found to be strongly correlated to the types and additional amounts of organic dyes, that the positive organic dyes allow for the preparation of > 7 mm bulks and negative dyes account for sub‐20 μm particles. This work opens a new avenue to fabricate full‐color emissive CPL composites and provides a potentially universal method for controlling the size of optical platforms.

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

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

D-π-A Type [7]Helicene-like Imide Derivatives with Tunable Photophysical Properties and Circularly Polarized Luminescence.

Helicenes and their derivatives show great application prospects as circularly polarized luminescence (CPL) materials, but their fluorescence quantum yields (ΦFLs) need a breakthrough urgently. Herein, we reported a series of D-π-A type helical luminescent emitters by combining the [7]helicene-like imide acceptor with five different donors. The obtained five emitters display blue-to-orange luminescence and markedly enhanced ΦFL. Notably, TPA-NiBTI exhibits the maximum ΦFL in solution, while TPE-NiBTI achieves a maximum ΦFL in the solid state. Their two pairs of enantiomers, (P/M)-TPA-NiBTI and (P/M)-TPE-NiBTI, exhibit remarkable CPL activities, and their doped PS film both displayed doubled ΦFLs. Among them, [(P/M)-TPE-NiBTI]-doped PS film exhibits the maximum luminescence dissymmetry factor (|glum|) value of 9.0×10-4 and the maximum ΦFL of 22%. This molecular design strategy presents a promising approach to improving the ΦFL of helicene derivatives, thereby facilitating their potential application into chiral optoelectronic devices.

Loading Dyes into Chiral Cd/Zn-Metal-Organic Frameworks for Efficient Full-Color Circularly Polarized Luminescence.

Host-guest chemistry of chiral metal-organic frameworks (MOFs) has endowed them with circularly polarized luminescence (CPL), it is still limited for MOFs to systematically tune full-color CPL emissions and sizes. This work directionally assembles the chiral ligands, metal sites and organic dyes to prepare a series of crystalline enantiomeric D/L-Cd/Zn-n MOFs (n=1~5, representing the adding amount of dyes), where D/L-Cd/Zn with the formula of Cd2(D/L-Cam)2(TPyPE) and Zn2(D/L-Cam)2(TPyPE) (D/L-Cam=D/L-camphoric acid, TPyPE=4,4',4'',4'''-(1,2-henediidenetetra-4,1-phenylene)tetrakis[pyridine]) were used as the chiral platforms. The framework-dye-enabled emission and through-space chirality transfer facilitate D/L-Cd/Zn-n bright full-color CPL activity. The ideal yellow CPL of D-Cd-5 and D-Zn-4, with |glum| as 4.9 × 10-3 and 1.3×10-3 and relatively high photoluminescence quantum yield of 40.79 % and 45.40 %, are further assembled into a white CPL light-emitting diode. The crystal sizes of D/L-Cd/Zn-n were found to be strongly correlated to the types and additional amounts of organic dyes, that the positive organic dyes allow for the preparation of > 7 mm bulks and negative dyes account for sub-20 μm particles. This work opens a new avenue to fabricate full-color emissive CPL composites and provides a potentially universal method for controlling the size of optical platforms.

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.

Binaphthalene-Assisted Axial Chirality in Porphyrins: Toward Solid-State Circularly Polarized Luminescence from Self-Assembled Nanostructures.

Circularly polarized luminescence (CPL) is emerging as an effective tool to study the excited-state optical activity in molecules and their self-assembled nanostructures. Chiral porphyrins are a class of optically active molecules wherein the ground-state chirality has been extensively studied in recent times using circular dichroism (CD) spectroscopy. However, obtaining CPL from porphyrin nanostructures, which would have vast implications in biological applications, has remained an uphill task. In this work, we design and synthesize a pair of chiral porphyrin enantiomers functionalized by axially chiral binaphthalene units at the four meso-positions. The molecule undergoes self-assembly following an isodesmic polymerization model, leading to the formation of a spherical nanostructure possessing opposite chirality. Favorable thermodynamic parameters achieved through the controlled experimental conditions helped drive the self-assembly in the forward direction. The limitations imposed by a large nonradiative decay constant arising due to the aggregation-induced quenching could be overcome by fabricating self-standing polymeric films of the nanostructures. The films exhibited relatively high radiative decay and, more interestingly, good CPL activity with clear mirror image spectra for the nanostructures with opposite chirality. The work on CPL-active solid-state materials opens avenue for the design and synthesis of a variety of porphyrin-based chromophoric systems and their nanoaggregates that can find potential application in the field of chiral biosensing and bioimaging, security tags, and display devices.

Ultrasound‐induced circularly polarized luminescence based on homochiral aggregation of clothespin‐shaped Pt(II) complexes

AbstractUltrasound‐induced circularly polarized luminescence (CPL) was achieved using planar chiral, binuclear clothespin‐shaped trans‐bis(salicylaldiminato)platinum(II) complexes. Solutions of the clothespin‐shaped platinum(II) complexes anti‐1a–c in cyclohexane immediately transformed into stable gels upon brief ultrasound irradiation. The ultrasound gels exhibited intense phosphorescent emissions at room temperature, whereas none of the solution exhibited significant emissions under UV light illumination. Interestingly, gels prepared from optically pure complexes exhibited CPL activity at room temperature with an anisotropy factor of |glum| = 1.5–2.6 × 10−3. The emissive gels were readily converted to the original non‐emissive solution upon heating and cooling to room temperature and could be gelled again by ultrasound irradiation. In addition, chromogenic control from green to red emission can be achieved simply by introducing MeO groups at different positions on the aromatic rings.

Molecular dyad exhibiting strong multi‐resonance blue fluorescence

AbstractA multi‐resonance (MR) fluorophore exhibiting circularly polarized luminescence (CPL) holds a significant promise for enhancing the utility of organic light‐emitting devices. To meet this demand, we have devised molecular dyads having azaoxaborin MR emitters based on homochiral (R)‐ and (S)‐1,1′‐bi‐2‐naphthol. The synthesized 12,12′‐di‐tert‐butyl‐9,9′‐bi(8,8′‐dioxa‐4b,4′b‐diaza‐14b,14′b‐diborafluorantheno[1,2,3‐de]tetracene) products (TBNBOCz) exhibit strong blue fluorescence, with a remarkable 100% fluorescence quantum yield and an extremely narrow full width at half‐maximum of 22 nm. However, unexpectedly, TBNBOCz exhibits negligible electric circular dichroism and CPL activities. Chiroptical investigations into the reaction precursors reveals an occurrence of racemization in the borylation step. This result emphasizes the importance of understanding synthetic processes and their impact on the chiroptical properties.

Metal Clusters Confined in Chiral Zeolitic Imidazolate Framework for Circularly Polarized-Luminescence Inks.

Chiroptical activities arising in nanoclusters (NCs) are emerging as one of the most dynamic areas of modern science. However, devising an overarching strategy that is capable of concurrently enhancing the photoluminescence (PL) and circularly polarized luminescence (CPL) of metal NCs remains a formidable challenge. Herein, gold and silver nanoclusters (AuNCs, AgNCs) are endowed with CPL, for the first time, through a universal host-guest approach─centered around perturbing a chiral microenvironment within chiral hosts, simultaneously enhancing emissions. Remarkably, the photoluminescence quantum yield (PLQY) of AuNCs has undergone an increase of over 200 times upon confinement, escalating from 0.05% to 12%, and demonstrates a CPL response. Moreover, a three-dimensional (3D) model termed "NCs@CMOF" featuring CPL activity is created using metal cluster-based assembly inks through the process of 3D printing. This work introduces a potentially straightforward and versatile approach for achieving both PL enhancement and CPL activities in metal clusters.

2.2]Paracyclophane‐Based Double Helices: Tunable Circularly Polarized Luminescence Driven by Self‐Assembly

AbstractAchieving high luminescence dissymmetry factors and quantum yields in the solid state remains a significant challenge in developing circularly polarized luminescence (CPL) materials. This study presents the synthesis of double helices based on planar chiral [2.2]paracyclophane ([2.2]PCP) and tetraphenylethylene (TPE), which exhibit chiroptical and aggregation‐induced emission (AIE) properties. In particular, the double helix with long alkyl chains demonstrates tunable CPL activity driven by self‐assembly, exhibiting dissymmetry factors ranging from 10−4 to 10−2. Notably, doped PMMA films show an amplified dissymmetry factor of 0.058 and a high quantum yield of up to 51%. The designed molecules represent an ideal molecular functional material for generating efficient CPL with controllable dissymmetry factor and high emission efficiency in the solid state. This opens up possibilities for applications in chiroptical sensing, data storage, and light‐emitting devices based on solid‐state materials.

Helical Cage Rotors Switched on by Brake Molecule with Variable Fluorescence and Circularly Polarized Luminescence.

While chiral molecular rotors have unique frames and cavities to possibly generate switchable chiroptical functions, it still remains a formidable challenge to precisely restrict their rotations to activate certain functions such as fluorescence as well as circularly polarized luminescence (CPL), which are strongly related to the local molecular rotations. Herein, we design a pair of enantiopure helical cage rotors, which emit light neither at the molecular state nor in the crystal or aggregation states, although they contain luminophore groups. However, upon mounting with fluoroaromatic borane (TFPB) as a molecular brake, the phenyl rotation of the helical cage can be effectively hindered and fluorescence and CPL activities of the molecular cage are switched on. Crystal structure analysis reveals that the rotation is restricted through synergistic B-O-H-N bonding and a fluoroaromatic-aromatic (ArF-Ar) dipole interaction. Moreover, the helical cages are switched on stepwise with color-variable fluorescence and CPL by the inner brake in the molecular state and the outer brake in the supramolecular assemblies, respectively. This work not only provides the design idea of chiroptical molecular rotors but also unveils how fluorescence and CPL could be generated in cage rotor systems.

Enhancing the Circularly Polarized Luminescence of Europium Coordination Polymers by Doping a Chromophore Ligand into Superhelices.

Lanthanide-based molecular materials showing efficient circularly polarized luminescence (CPL) activity with a high quantum yield are attractive due to their potential applications in data storage, optical sensors, and 3D displays. Herein we present an innovative method to achieve enhanced CPL activity and a high quantum yield by doping a chromophore ligand into a coordination polymer superhelix. A series of homochiral europium(III) phosphonates with a helical morphology were prepared with the molecular formula S-, R-[Eu(cyampH)3-3n(nempH)3n]·3H2O (S/R-Eu-n, n = 0-5%). The doping of chromophore ligand S- or R-nempH2 into superhelices of S/R-Eu-0% not only turned on the CPL activity with the dissymmetry factor |glum| on the order of 10-3 but also increased the quantum yield by about 14-fold. This work may shed light on the development of efficient CPL-active lanthanide-based coordination polymers for applications.

Chiral Carbon Dots and Chiral Carbon Dots with Circularly Polarized Luminescence: Synthesis, Mechanistic Investigation and Applications.

Chiral carbon dots (CCDs) can be widely used in various fields such as chiral recognition, chiral catalysis and biomedicine because of their unique optical properties, low toxicity and good biocompatibility. In addition, CCDs with circularly polarized luminescence (CPL) can be synthesized, thus broadening the prospects of CCDs applications. Since the research on CCDs is still in its infancy, this paper reviews the chiral origin, formation mechanism, chiral evolution, synthesis and emerging applications of CCDs, with a special focus on CCDs with CPL activity. It is hoped that it will provide some reference to solve the current problems faced by CCDs. Finally, the opportunities and challenges of the current research on CCDs are described, and their future development trends have also been prospected.

Chiral Deep Eutectic Solvents Enable Full‐Color and White Circularly Polarized Luminescence from Achiral Luminophores

AbstractHerein, chiral deep eutectic solvents (DES) are prepared by lauric acid as hydrogen bond donors (HBD) and chiral menthol as hydrogen bond acceptors (HBA). When achiral fluorescent molecules are dopedin the menthol‐based chiral DES, they emit circularly polarized luminescence (CPL) with handedness controlled by the molecular chirality (l or d) of menthol. Remarkably, the strategy is universal and a series of achiral fluorescent molecules can be endowed with CPL activity, showing a full‐color and white CPL upon appropriate mixing, which paves the way to prepare white CPL materials. Interestingly, CPL appears only in a certain temperature range in the DES. Variable‐temperature spectra and other characterization methods reveal that the H‐bond network in the chiral DES plays an important role in inducing CPL. This work unveils how the interior structure as well as the hydrogen‐bond network of a chiral DES can transfer its chirality to achiral luminophores for the first time and realizes a full‐color and white CPL in a DES.

Chiral Deep Eutectic Solvents Enabled Full-color and White Circularly Polarized Luminescence from Achiral Luminophore.

Herein, chiral deep eutectic solvents (DES) are prepared by lauric acid as hydrogen bond donors (HBD) and chiral menthol as the hydrogen bond acceptors (HBA). When achiral fluorescent molecules are doped into the menthol-based chiral DES, they emit circularly polarized luminescence (CPL) with handedness controlled by the molecular chirality (L or D) of menthol. Remarkably, the strategy is universal and a series of achiral fluorescent molecules can be endowed CPL activity, showing a full-color and white CPL upon appropriate mixing, which paves a convenient way to prepare white CPL materials. Interestingly, CPL appears only in a certain temperature range in DES. Variable-temperature spectra and other characterization method reveal that the H-bond network in the chiral DES plays an important role in inducing CPL. The work unveils how the interior structure as well as the hydrogen bond network of chiral DES transfer their chirality to the achiral luminophores for the first time and realizes a full-color and white CPL in DES.

Excitation-Dependent Fluorescence with Excitation-Selective Circularly Polarized Luminescence from Hierarchically Organized Atomic Nanoclusters.

Nanometer-scaled objects are known to have dimension-related properties, but sometimes the assembly of such objects can lead to the emergence of other properties. Here, we show the assembly of atomically precise gold nanoclusters into large fibrillar structures that are featuring excitation-dependent luminescence with an excitation-selective circularly polarized luminescence (CPL), even though all components are achiral. The origin of CPL in the assembly of atomic clusters has been attributed to the hierarchical organization of atomic clusters into fibrillar structures, mediated via a hydrogen bonding interaction with a surfactant. We follow the assembly process both experimentally and computationally showing the advance in the structural formation along with its chiroptical electronic properties, i.e., circular dichroism (CD) and CPL. Our study here can assist in the rational design of materials featuring chiroptical properties, thus leading to a controlled CPL activity.

Multiple Stimuli‐Responsive Luminescent Chiral Hybrid Antimony Chlorides for Anti‐Counterfeiting and Encryption Applications

AbstractStimuli‐responsive circularly polarized luminescence (CPL) materials are ideal for information anti‐countering applications, but the best‐performing materials have not yet been identified. This work presents enantiomorphic hybrid antimony halides R‐(C5H12NO)2SbCl5 (1) and S‐(C5H12NO)2SbCl5 (2) showing mirror‐imaged CPL activity with a dissymmetry factor of 1.2×10−3. Interestingly, the DMF‐induced structural transformation is realized to obtain non‐emissive R‐(C5H12NO)2SbCl5 ⋅ DMF (3) and S‐(C5H12NO)2SbCl5 ⋅ DMF (4) upon exposure to DMF vapor. The transformation process is reversed upon heating. DFT calculations showed that the DMF‐induced‐quenched‐luminescence is attributed to the intersection of the ground and excited state curves on the configuration coordinates. Unexpectedly, the nanocrystals of the chiral antimony halides 1 and 2 were prepared and indicate the excellent solution process performance. The reversible PL and CPL switching gives the system applications in information technology, anti‐counterfeiting, encryption‐decryption, and logic gates.

Multiple Stimuli-Responsive Luminescent Chiral Hybrid Antimony Chlorides for Anti-Counterfeiting and Encryption Applications.

Stimuli-responsive circularly polarized luminescence (CPL) materials are ideal for information anti-countering applications, but the best-performing materials have not yet been identified. This work presents enantiomorphic hybrid antimony halides R-(C5 H12 NO)2 SbCl5 (1) and S-(C5 H12 NO)2 SbCl5 (2) showing mirror-imaged CPL activity with a dissymmetry factor of 1.2×10-3 . Interestingly, the DMF-induced structural transformation is realized to obtain non-emissive R-(C5 H12 NO)2 SbCl5 ⋅ DMF (3) and S-(C5 H12 NO)2 SbCl5 ⋅ DMF (4) upon exposure to DMF vapor. The transformation process is reversed upon heating. DFT calculations showed that the DMF-induced-quenched-luminescence is attributed to the intersection of the ground and excited state curves on the configuration coordinates. Unexpectedly, the nanocrystals of the chiral antimony halides 1 and 2 were prepared and indicate the excellent solution process performance. The reversible PL and CPL switching gives the system applications in information technology, anti-counterfeiting, encryption-decryption, and logic gates.

Helical Polymer Working as a Chirality Amplifier to Generate and Modulate Multicolor Circularly Polarized Luminescence in Small Molecular Fluorophore/Polymer Composite Films.

In-depth studies of chirality and circularly polarized luminescence (CPL) have become indispensable in the process of learning human nature. Small molecules with CPL activity are one of the research hotspots. However, the CPL properties of such materials are generally not satisfying. Here, we synthesized a series of chiral small molecular fluorophores that cannot demonstrate CPL emission themselves. By introducing an optically inactive helical polymer, chirality transfer and chirality amplification efficiently occur, thereby generating intense CPL emission. Through combining different chiralized fluorophores, multicolor CPL-active films with emission wavelength centered at 463, 525, and 556 nm were fabricated, with the maximum luminescence dissymmetry factor (glum) being up to -0.028. Then, benefiting from the strong CPL emission and appropriate energy donor-acceptor system, we further established a circularly polarized fluorescence-energy transfer (CPF-ET) strategy in which the CPL-active films work as a donor emitting circularly polarized fluorescence to excite an achiral fluorophore (Nile red) as the acceptor, producing red CPL with glum of up to -0.011 at around 605 nm.