Dissymmetry Factor Research Articles

Processable Circularly Polarized Luminescence for the Synthesis of Chiral Plasmonic Nanoparticles

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

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

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

Remote chirality transfer in low-dimensional hybrid metal halide semiconductors.

In hybrid metal halide perovskites, chiroptical properties typically arise from structural symmetry breaking by incorporating a chiral A-site organic cation within the structure, which may limit the compositional space. Here we demonstrate highly efficient remote chirality transfer where chirality is imposed on an otherwise achiral hybrid metal halide semiconductor by a proximal chiral molecule that is not interspersed as part of the structure yet leads to large circular dichroism dissymmetry factors (gCD) of up to 10-2. Density functional theory calculations reveal that the transfer of stereochemical information from the chiral proximal molecule to the inorganic framework is mediated by selective interaction with divalent metal cations. Anchoring of the chiral molecule induces a centro-asymmetric distortion, which is discernible up to four inorganic layers into the metal halide lattice. This concept is broadly applicable to low-dimensional hybrid metal halides with various dimensionalities (1D and 2D) allowing independent control of the composition and degree of chirality.

π‐Extension of a Multiple Resonance Core: Double Helical and Heptagon‐Embedded Nanographenes

AbstractMultiple resonance (MR) boron–nitrogen doped polycyclic aromatic hydrocarbons (BN‐PAHs) have shown compelling thermally activated delayed fluorescence (TADF), surpassing those of their hydrocarbon analogues. However, the structural variety of π‐extended BN‐PAHs remains narrow. In this study, we synthesized three double helical BN‐doped nanographenes (BN‐NGs), 2 a–2 c, and three heptagon‐embedded BN‐NGs, 1 a–1 c, by π‐extension of the MR core. During the formation of 2 a, a nanographene with one heptagon (1 a) was obtained, whereas further dehydrocyclization of the [6]helicene units within 2 b and 2 c led to heptagon structures, yielding other two BN‐NGs containing double heptagons (1 b and 1 c). These BN‐NGs (2 a–2 c and 1 a–1 c) showed pronounced redshifts of 100–190 nm compared to the parent MR core, while preserving the TADF characteristics and prolonging the delayed fluorescence lifetime to the millisecond level. Furthermore, the integration of a heptagon ring into 1 a–1 c expanded the conjugation, reduced the oxidation potentials, and yielded a more flexible framework compared to those of 2 a–2 c. The enantiomers of 2 a–2 c, 1 a, and 1 c were resolved and their chiroptical properties were studied. Notably, 1 a and 1 c exhibited increased chiroptical dissymmetry factors.

π-Extension of a Multiple Resonance Core: Double Helical and Heptagon-Embedded Nanographenes.

Multiple resonance (MR) boron-nitrogen doped polycyclic aromatic hydrocarbons (BN-PAHs) have shown compelling thermally activated delayed fluorescence (TADF), surpassing those of their hydrocarbon analogues. However, the structural variety of π-extended BN-PAHs remains narrow. In this study, we synthesized three double helical BN-doped nanographenes (BN-NGs), 2 a-2 c, and three heptagon-embedded BN-NGs, 1 a-1 c, by π-extension of the MR core. During the formation of 2 a, a nanographene with one heptagon (1 a) was obtained, whereas further dehydrocyclization of the [6]helicene units within 2 b and 2 c led to heptagon structures, yielding other two BN-NGs containing double heptagons (1 b and 1 c). These BN-NGs (2 a-2 c and 1 a-1 c) showed pronounced redshifts of 100-190 nm compared to the parent MR core, while preserving the TADF characteristics and prolonging the delayed fluorescence lifetime to the millisecond level. Furthermore, the integration of a heptagon ring into 1 a-1 c expanded the conjugation, reduced the oxidation potentials, and yielded a more flexible framework compared to those of 2 a-2 c. The enantiomers of 2 a-2 c, 1 a, and 1 c were resolved and their chiroptical properties were studied. Notably, 1 a and 1 c exhibited increased chiroptical dissymmetry factors.

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

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

Hollow Superhelices Based on Chiral Europium Coordination Polymers.

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

Higly Luminescent Aceno[6]helicenones by Intramolecular Radical Cyclization.

Helicenes and helicenoid structures are promising candidates for future applications exploiting circularly polarized light. Ideal candidates should possess near-quantitative photoluminescence quantum yield, high a luminescence dissymmetry factor and an adjustable HOMO-LUMO gap. However, carbo[n]helicenes are poorly luminescent compounds and they absorb light mainly in the ultraviolet region. Here we show that the incorporation of a carbonyl group into helical scaffold significantly improves the fluorescence quantum yield and shifts the absorption to visible region. Although the carbonyl group is commonly considered as detrimental to efficient emission, fluorescence quantum yields up to Φ = 0.43 were recorded. A straightforward synthetic approach to a highly luminescent tetraceno[6]helicenone and an aza analogue has been developed. The key step is a radical cyclization which is achieving dehydrative π-extension. The aza-analogue was incorporated as an emitter in organic light emitting diodes (OLEDs) and showed good performance.

Phosphetene-Based Polyaromatics: Structure-Property Relationships and Chiroptical Tuning.

We describe the synthesis of π-extended phosphetene rings (4-member P-rings) flanked with PAH systems of various topologies. These compounds are fully characterized including X-ray diffraction. The impact of both the polyaromatic platform and the P-ring on the structure, and the optical and redox properties are investigated both experimentally and theoretically. Although neither the P centre nor the 4-membered ring significantly takes part in the HOMO or LUMO orbitals, both structural features have an important modulating role in distorting the symmetry of the orbitals, leading to chiroptical properties. The stereogenic P-atom is used as a remote chiral perturbator to induce circularly polarized luminescence of the polyaromatic system. The dissymmetry factor is highly dependent on the polyaromatic topology, as supported by theoretical calculations.

A Chiral Propeller‐Shaped Triple Helicene Shows Multi‐Resonant Thermally Activated Delayed Fluorescence

Multi‐resonant thermally activated delayed fluorescence (MR‐TADF) helicenes show great potential as chiral emitters due to their typically high photoluminescence quantum yield and that they emit circularly polarized luminescence. Here, a new propeller‐shaped chiral MR‐TADF helicene DiKTa3, integrating three DiKTa moieties, was designed and synthesized aiming to achieve co‐parallel electronic and magnitude transition dipole moments that would lead to a high dissymmetry factor, g. It emits at λPL of 491 nm, with a full width at half maximum of 52 nm and has a moderate ΔEST value of 0.24 eV in toluene. The separated (P,P,P) enantiomer shows an absorption dissymmetry factor |gabs| of 6.8 × 10‐4 at 450 nm, which results from a lower symmetry conformation adopted by the compound in solution than the C3‐symmetric optimized structure. This work highlights the strong influence that geometry can have on the chiroptical properties of the emitter.

Switchable Topologically Chiral [2]Catenane as Multiple Resonance Thermally Activated Delayed Fluorescence Emitter for Efficient Circularly Polarized Electroluminescence.

Aiming at the fabrication of circularly polarized organic light-emitting diodes (CP-OLEDs) with high dissymmetry factors (gEL) and color purity through the employment of novel chiral source, topologically chiral [2]catenanes were first utilized as the key chiral skeleton to construct novel multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters. Impressively, the efficient chirality induction and unique switchable feature of topologically chiral [2]catenane not only lead to a high |gPL| value up to 1.6 × 10-2 but also facilitate in situ dynamic switching of the full-width at half-maximum (FWHM) and circularly polarized luminescence (CPL). Furthermore, the solution-processed CP-OLEDs based on the resultant topologically chiral emitters exhibit reveal narrow FWHM of 36 nm, maximum external quantum efficiency of 17.6%, and CPEL with |gEL| of 2.1 × 10-3. This study demonstrates the successful construction of the first CP-MR-TADF emitters based on topological chirality with the highest |gPL| among the reported CP-MR-TADF emitters and excellent device performance to the best of our knowledge. Moreover, it endowed the MR-TADF emitter with distinctive switchable CPL performances, thus providing a novel design strategy as well as a promising platform for developing intelligent CP-OLEDs.

Switchable Topologically Chiral [2]Catenane as Multiple Resonance Thermally Activated Delayed Fluorescence Emitter for Efficient Circularly Polarized Electroluminescence

Aiming at the fabrication of circularly polarized organic light‐emitting diodes (CP‐OLEDs) with high dissymmetry factors (gEL) and color purity through the employment of novel chiral source, topologically chiral [2]catenanes were first utilized as the key chiral skeleton to construct novel multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters. Impressively, the efficient chirality induction and unique switchable feature of topologically chiral [2]catenane not only lead to a high |gPL| value up to 1.6 × 10‐2 but also facilitate in situ dynamic switching of the full‐width at half‐maximum (FWHM) and circularly polarized luminescence (CPL). Furthermore, the solution‐processed CP‐OLEDs based on the resultant topologically chiral emitters exhibit reveal narrow FWHM of 36 nm, maximum external quantum efficiency of 17.6%, and CPEL with |gEL| of 2.1 × 10‐3. This study demonstrates the successful construction of the first CP‐MR‐TADF emitters based on topological chirality with the highest |gPL| among the reported CP‐MR‐TADF emitters and excellent device performance to the best of our knowledge. Moreover, it endowed the MR‐TADF emitter with distinctive switchable CPL performances, thus providing a novel design strategy as well as a promising platform for developing intelligent CP‐OLEDs.

Magneto‐Chiral Dichroism of Chiral Lanthanide Complexes in the Context of Richardson’s Theory of Optical Activity

Here we report on the Magneto‐Chiral Dichroism (MChD) detected through visible and near‐infrared light absorption of two enantiomeric pairs of ErIII and TmIII chiral complexes featuring a propeller‐like molecular structure. The magnetic properties show typical features of isolated paramagnetic ions associated with 4I15/2 and 3H6 ground state terms. MChD spectroscopy shows high gMChD dissymmetry factors of ca. 0.12 T‐1 and 0.05 T‐1 (T = 4.0 K and B = 1.0 T) for ErIII and TmIII, respectively, associated with their magnetic‐dipole allowed 4I13/2 ← 4I15/2 and 3H5 ← 3H6 transitions. MChD signals of the two complexes were detected up to room temperature and under magnetic fields up to 5.0 T. For the first time, the MChD results reported here are discussed in the context of the Richardson theory of lanthanide optical activity and provide clear indications on the strongest MChD‐active electronic transitions of lanthanide complexes.

Magneto-Chiral Dichroism of Chiral Lanthanide Complexes in the Context of Richardson's Theory of Optical Activity.

Here we report on the Magneto-Chiral Dichroism (MChD) detected through visible and near-infrared light absorption of two enantiomeric pairs of ErIII and TmIII chiral complexes featuring a propeller-like molecular structure. The magnetic properties show typical features of isolated paramagnetic ions associated with 4I15/2 and 3H6 ground state terms. MChD spectroscopy shows high gMChD dissymmetry factors of ca. 0.12 T-1 and 0.05 T-1 (T = 4.0 K and B = 1.0 T) for ErIII and TmIII, respectively, associated with their magnetic-dipole allowed 4I13/2 ← 4I15/2 and 3H5 ← 3H6 transitions. MChD signals of the two complexes were detected up to room temperature and under magnetic fields up to 5.0 T. For the first time, the MChD results reported here are discussed in the context of the Richardson theory of lanthanide optical activity and provide clear indications on the strongest MChD-active electronic transitions of lanthanide complexes.

A Dynamic H-Bonding Network Enables Stimuli-Responsive Color-Tunable Chiral Afterglow Polymer for 4D Encryption.

The development of stimuli-responsive and color-tunable chiral organic afterglow materials has attracted great attention but remains a daunting challenge. Here, a simple yet effective strategy through the construction of a dynamic H-bonding network is proposed to explore the multi-color stimuli-responsive chiral afterglow by doping a self-designed chiral phosphorescent chromophore into a polyvinyl alcohol matrix. A stimuli-responsive deep blue chiral afterglow system with a lifetime of up to 3.35 s, quantum yield of 25.0%, and luminescent dissymmetry factor of up to 0.05 is achieved through reversible formation and breakdown of the H-bonding network upon thermal-heating and water-fumigating. Moreover, multi-color stimuli-responsive chiral afterglow can be obtained by chiral and afterglow energy transfer, allowing the establishment of afterglow information displays and high-level 4D encryption. This work not only offers a facile platform to develop advanced stimuli-responsive materials but also opens a new avenue for developing next-generation optical information technology with enhanced functionality and responsiveness.

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.

Color-Tunable Lead Halide Perovskite Single-Mode Chiral Microlasers with Exceptionally High glum.

Chiral microlasers hold great promise for optoelectronics from integrated photonic devices to high-density quantum information processing. Despite significant progress in lead-halide perovskite emitters, chiral lasing with high dissymmetry factors (glum) has not yet been realized. Here, we demonstrate chiral single-mode microlasers with exceptional stability and tunable emission across the visible range by combining CsPbClxBr3-x perovskite microrods (MRs) with a cholesteric liquid crystal (CLC) layer. The MRs lase via a whispering gallery mode (WGM) microcavity and confer chirality through the encapsulated CLC layer, thus exhibiting circularly polarized lasing with dissymmetry factors reaching 1.62. Importantly, we demonstrate wavelength-tunable high dissymmetry chiral lasers in a broad spectral range by tuning the halide composition and using CLC layers with the desired photonic bandgap (PBG). This facile approach to generate chiral lasing not only is applicable to semiconductor nano- and microcrystals but also paves the way for potential integration into nanoscale photonic devices.

Synthesis and characterization of a chiral spirobifluorene cyclic hexamer

Abstract A new chiral macrocycle 1-[6], consisting of six chiral spirobifluorene units linked in a cyclic arrangement, was successfully synthesized via a homo-coupling of the corresponding acyclic trimer. Notably, this chiral cyclic hexamer exhibited flexibility in solution, and both low-temperature nuclear magnetic resonance (NMR) experiments and density functional theory (DFT) calculations suggest that its stable structure is not the hexagonal D6-symmetric structure but rather the figure-eight-shaped D2-symmetric structure. In this D2-symmetric structure, the opposing bifluorenyl units are π-stacked, and it is suggested that this π-stacked region undergoes rapid dissociation and reformation at room temperature. The HOMO is distributed over the π-stacked region, with a HOMO-LUMO gap of 4.02 eV. The macrocycle exhibited strong violet fluorescence. The absorption dissymmetry factor |gabs| was 7.4 × 10−3, which is larger compared to the series of chiral smaller macrocycles 1-[n] (n = 3 to 5). Additionally, the CPL efficiency, indicated by a BCPL value of 189 M−1 cm−1, is relatively high among chiral organic luminescent molecules.

Ring-Size Control and Guest-Induced Circularly Polarized Luminescence in Heteroleptic Pd3A3B3 and Pd4A4B4 Assemblies.

Two new structural motifs within the class of heteroleptic PdnAnBn assemblies, namely syn-cis-Pd3A3B3 bowls and bowl- (syn) or saddle- (anti) shaped cis-Pd4A4B4 rings are introduced. All of the ten examples share a common longer fluorenone-based bis-monodentate ligand, equipped with meta-pyridine donor groups. The ring size (3- vs. 4-membered) and conformational preference (bowl vs. saddle) are controlled by the choice of the shorter ligand. These carry para-pyridine donors, different aromatic backbones (benzene, thiophene or selenophene) and either no or small or bulky endohedral substituents, serving to control the nuclearity of the heteroleptic rings through different effects (ligand angle, charge distribution or backbone bulk). Moreover, the luminescence of the fluorenone ligand is conserved in the formed architectures. Emission intensity as well as host-guest properties vary depending on the inward-pointing functions. All Pd3A3B3 assemblies are shown to bind chiral guest BINOL bis-sulfonate which imparts its chirality to the entire host-guest complex. This results in a guest-induced circular dichroism (CD) and circularly polarized luminescence (CPL) with dissymmetry factor glum up to 10-3.

Enhancing Circularly Polarized Luminescence Dissymmetry Factor of Chiral Cylindrical Molecules to -0.56 through Intramolecular Short-Range Charge Transfer.

High-performance circularly polarized luminescent (CPL) materials have received wide attention recently by virtue of broad application in circularly polarized light-emitting diodes, 3D display, and encryption. Reaching both high luminescence efficiency and strong luminescence dissymmetry factor (glum) is still a challenging goal that requires continuous efforts. Herein, we performed a systematic theoretical investigation on the chiroptical properties of helical cylindrical molecules (-)-[4]cyclo-2,6-anthracene [(-)-[4]CA2,6] and (P)-[4]cyclo-2,8-chrysenylene [(P)-[4]CC2,8], and found that the unique and symmetric cylindrical structure could make the transition dipole moment components offset along the cylindrical surface but concentrated along the vertical central axis. This structural superiority contributes the collinear electric and magnetic transition dipole moment vectors and thus the large glum. Based on the results of decomposed transition dipole moment vectors to individual atoms, an effective strategy to enhance the glum through introducing intramolecular short-range charge transfer by embedding B,N atoms is proposed. The decreased electric transition dipole moment and well-kept magnetic transition dipole moment enable the glum of B,N-embedded designed molecules (-)-[4]CA2,6-4BN and (P)-[4]CC2,8-4BN up to -0.31 and -0.56, respectively. This molecular-insight investigation deepens the understanding of the structure-property relationship and provides efficient guidance for improving glum of CPL materials.