Chiroptical Properties Research Articles

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

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

High-Fidelity Supramolecular Chirality Transportation Enabled Through Chalcogen Bonding.

The formation of asymmetric microenvironments in proteins benefits from precise transportation of chirality across multiple levels through weak bonds in the folding and assembly process, which inspires the rational design and fabrication of artificial chiral materials. Herein, the chalcogen bonding-directed precise transportation of supramolecular chirality toward multiple levels is reported to aid the fabrication of chiroptical materials. Benzochalcogenadiazole (O, S, Se) motifs are conjugated to amino acid residues, and the solid-state assemblies afforded selective supramolecular chirality with handedness depending on the kinds of chalcogen atoms and amino acids. The chalcogen-N sequence assisted by hydrogen bonding synergistically allows for the complexation with pyrene conjugated aryl carboxylic acids to give macroscopic helical structures with active circular dichroism and circularly polarized luminescence, of which handedness is precisely determined by the pristine chiral species. Then the further application of chiral benzochalcogenadiazole motifs as seeds in directing handedness of benzamide via symmetry breaking is realized. Behaving as the dopants, embedding into the matrix of benzophenone induces the room temperature phosphorescence, whereby the thermal chiroptical switch is fabricated with color-tunable phosphorescent circularly polarized luminescence. This work utilized benzochalcogenadiazole-based chiral building units to accomplish precise transportation of supramolecular chirality in coassemblies with high-fidelity, achieving flexible manipulation of chiroptical properties and macroscopic helical sense.

5]Helicene Based π‐Conjugated Macrocycles with Persistent Figure‐Eight and Möbius Shapes: Efficient Synthesis, Chiral Resolution and Bright Circularly Polarized Luminescence

π‐Conjugated chiral shape‐persistent molecular nanocarbons hold great potential as chiroptical materials, though their synthesis remains a considerable challenge. Here, we present a simple approach using Suzuki coupling of a [5]helicene building block with various aromatic units, enabling the one‐pot synthesis of a series of chiral macrocycles with persistent figure‐eight and Möbius shapes. Single‐crystal structures of 7 compounds were solved, and 22 enantiomers were separated by preparative chiral HPLC. A notable pyrene‐bridged figure‐eight macrocycle, with its rigid, fully π‐conjugated and overcrowded structure, exhibited pure excimer emission and outstanding circularly polarized luminescence (CPL) properties, including a large dissymmetric factor (|glum| = 3.8 × 10−2) and significant CPL brightness (BCPL = 710.5 M‐1cm‐1). This method provides a versatile synthetic platform for producing various chiral D2‐symmetric figure‐eight macrocycles and singly or triply twisted Möbius macrocycles with C2 and D3 symmetry, offering tunable chiroptical properties for CPL applications.

Phonon-Induced Geometric Chirality.

Chiral properties have seen increasing use in recent years, leading to the emerging fields of chiral quantum optics, plasmonics, and phononics. While these fields have achieved manipulation of the chirality of light and lattice vibrations, controlling the chirality of materials on demand has yet remained elusive. Here, we demonstrate that linearly polarized phonons can be used to induce geometric chirality in achiral crystals when excited with an ultrashort laser pulse. We show that nonlinear phonon coupling quasistatically displaces the crystal structure along phonon modes that reduce the symmetry of the lattice to that of a chiral point group corresponding to a chiral crystal. By reorienting the polarization of the laser pulse, the two enantiomers can be induced selectively. Therefore, geometric chiral phonons enable the light-induced creation of chiral crystal structures and therefore the engineering of chiral electronic states and optical properties.

Chiral Organometallic Complexes Derived from Helicenic N-Heterocyclic Carbenes (NHCs): Design, Structural Diversity, and Chiroptical and Photophysical Properties.

ConspectusRecently, helicene derivatives have emerged as an important class of molecules with potential applications spanning over asymmetric catalysis, biological activity, magnetism, spin filtering, solar cells, and polymer science. To harness their full potential, especially as emissive components in circularly polarized organic light-emitting diodes (CP-OLEDs), generating structural chemical diversity and understanding the resulting photophysical and chiroptical properties are crucial. In this Account, we shed light on chemical engineering combining helicene and N-heterocyclic carbene (NHC) chemistries to create transition-metal complexes with unique architectures and describe their photophysical and chiroptical attributes. The σ-donating and π-accepting capabilities of the helically chiral π-conjugated NHCs endow the complexes with remarkable structural and electronic features. These characteristics manifest in phenomena such as chirality induction, very long-lived phosphorescence, and strong chiroptical signatures (electronic circular dichroism and circularly polarized luminescence).We describe the different classes of ligands primarily developed in our group by classifying them according to their connection between the helicenic moiety and the imidazole precursor. This connection is essential in determining the degree of π-conjugation and characterizing the emissive state. We comprehensively discuss 6-coordinate, 4-coordinate, and 2-coordinate complexes, delving into their structural nuances and examining how the interplay between metals and auxiliary ligands shapes their photophysical properties, with interpretations enriched by DFT calculations. Helicenes are known to promote intersystem crossing thanks to strong spin-orbit coupling, while metals offer robust frameworks leading to a variety of molecular architectures with specific topologies together with distinct excited-state properties. The electronic configurations and energy levels of the ligand and metal orbitals thus significantly modulate the photophysical and chiroptical behaviors of these complexes. In-depth analysis of chiroptical properties, notably electronic circular dichroism and circularly polarized luminescence, emphasizes the influence of different stereogenic elements on the chiroptical responses across various energy ranges with appealing "match-mismatch" effects. Finally, we describe future prospects of helicene NHCs, particularly in the context of emerging research on cost-effective and abundant transition metals for materials science and for photocatalysis. Indeed, the inherent long-lived MLCT, excited-state delocalization, structural rigidity, and intrinsic chirality of these complexes present intriguing avenues for future investigations.

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.

Double [5]carbohelicene: facile synthesis, chiroptical properties, isomerization study, and lasing application

Double [5]carbohelicene: facile synthesis, chiroptical properties, isomerization study, and lasing application

Helical Polyallenes: From Controlled Synthesis to Distinct Properties.

Polyallenes with appropriate pendants can form stable helices and exhibit significant optical activity. These helical polyallenes contain reactive double bonds that allow for further functionalization, making them a class of chiral functional materials with broad application prospects. This review article delves into the intricacies of synthesizing well-defined helical polyallenes through controlled synthetic methodologies, including helix-sense selective living polymerization, regioselective and asymmetric living polymerization, and one-pot block copolymerization of allenes with aryl monomers. The systemically outlined characteristics of the resulting helical polyallenes and related copolymers are summarized include their unique chiroptical properties, stimuli-responsiveness, helix-induced chiral self-assembly, and circularly polarized luminescence (CPL). Additionally, current challenges and future perspectives in the research of controlled synthesis, functionalities, and applications of helical polyallenes are discussed in detail.

Tuning the circularly polarized luminescence in homoleptic and heteroleptic chiral CrIII complexes.

A series of highly emissive inert and chiral CrIII complexes displaying positive and negative circularly polarized luminescence (CPL) within the near-infrared (NIR) region at room temperature have been prepared and characterized to decipher the effect of ligand substitution on the photophysical properties, more specifically on the chiroptical properties. The helical homoleptic [Cr(dqp-R)2]3+ (dqp = 2,6-di(quinolin-8-yl)pyridine; R = Ph, ≡-Ph, DMA, ≡-DMA (DMA = N,N-dimethylaniline)) and heteroleptic [Cr(dqp)(L)]3+ (L = 4-methoxy-2,6-di(quinolin-8-yl)pyridine (dqp-OMe) or L = N 2,N 6-dimethyl-N 2,N 6-di(pyridin-2-yl)pyridine-2,6-diamine (ddpd)) molecular rubies were synthesized as racemic mixtures and then resolved and isolated into their respective pure PP and MM enantiomeric forms by chiral stationary phase HPLC. The corresponding enantiomers show two opposite polarized emission bands within the 700-780nm range corresponding to the characteristic metal-centered Cr(2E'→4A2) and Cr(2T1 '→4A2) transitions with large g lum ranging from 0.14 to 0.20 for the former transition. In summary, this study reports the rational use of different ligands on CrIII and their effect on the chiroptical properties of the complexes.

Optical and Chiroptical Stimuli-Responsive Chiral AgNPs@H-Leu-Poly(phenylacetylene) Nanocomposites in Water.

Dynamic macroscopically chiral nanocomposites are prepared by combining silver nanoparticles (AgNPs) and dynamic helical poly(phenylacetylene)s (PPAs) bearing pendants functionalized with amino groups. These amino groups provide the nanocomposite with the ability to disperse in water along with high stability due to the interaction between the ammonium group and the AgNP. Moreover, the equilibrium between NH3+/NH2 produces a "blinking" contact between the PPA and the AgNPs, which allows total control of the dynamic helical behavior of the polymer. The use of acidic or neutral pH allows controlling the morphology of the nanocomposite, which consists of a nanosphere that has trapped inside it a single AgNP (pH = 2) or several AgNPs (pH = 7) with ca. 30 nm of diameter. These nanocomposites combine the optical and chiroptical stimuli-responsive properties of both components, AgNPs and PPAs. Thus, the controlled aggregation of the nanocomposite produced variations in the LSPR band of the AgNPs in a reversible manner. In turn, given that the chiral coating is selective to Ba2+, the presence of this metal ion caused a helical inversion of the chiral coating of the nanocomposite detected by electronic circular dichroism. Moreover, it is possible to distinguish between three metal ions in different oxidation states, such as Ce4+, Fe3+, and Hg2+, which produce different responses of the nanocomposite when oxidizing the AgNP to Ag+.

Upconversion/Downshifting Circularly Polarized Luminescence over 1200 nm in a Single Nanoparticle for Optical Anticounterfeiting and Information Encryption.

Multimodal upconversion and downshifting circularly polarized luminescent materials hold significant potential for optical anticounterfeiting applications due to their exceptional chiroptical properties. However, constructing these materials within a single emitter remains challenging. In this study, a conceptual model of multimodal up-conversion/downshifting circularly polarized luminescence (CPL) is realized within a single nanoparticle. A new type of nanoparticles with multilayer core-shell architecture is fabricated, capable of delivering upconversion/downshifting luminescence, when excited by a 980 nm laser. Utilizing a co-assembly strategy, multimodal upconversion/downshifting CPL emission, covering a broad emission range from ultraviolet (UV) to the second near-infrared (NIR-II) region, can be realized at the supramolecular level. These chiroptical properties closely follow the chirality of host matrix and are strongly dependent on the distribution mode of nanoparticles within the matrix films. The multimodal upconversion/downshifting CPL behavior enabled cutting-edge encryption applications including optical anticounterfeiting and information encryption. This work introduces a novel approach to designing multimodal upconversion/downshifting CPL materials and opens new avenues for the development of chiroptical functional materials.

Upconversion/Downshifting Circularly Polarized Luminescence over 1200 nm in a Single Nanoparticle for Optical Anticounterfeiting and Information Encryption

Multimodal upconversion and downshifting circularly polarized luminescent materials hold significant potential for optical anticounterfeiting applications due to their exceptional chiroptical properties. However, constructing these materials within a single emitter remains challenging. In this study, a conceptual model of multimodal up‐conversion/downshifting circularly polarized luminescence (CPL) is realized within a single nanoparticle. A new type of nanoparticles with multilayer core‐shell architecture is fabricated, capable of delivering upconversion/downshifting luminescence, when excited by a 980 nm laser. Utilizing a co‐assembly strategy, multimodal upconversion/downshifting CPL emission, covering a broad emission range from ultraviolet (UV) to the second near‐infrared (NIR‐II) region, can be realized at the supramolecular level. These chiroptical properties closely follow the chirality of host matrix and are strongly dependent on the distribution mode of nanoparticles within the matrix films. The multimodal upconversion/downshifting CPL behavior enabled cutting‐edge encryption applications including optical anticounterfeiting and information encryption. This work introduces a novel approach to designing multimodal upconversion/downshifting CPL materials and opens new avenues for the development of chiroptical functional materials.

Perylene‐Embedded Helical Nanographenes with Emission up to 1010 nm: Synthesis, Structures, and Chiroptical Properties

Perylene‐Embedded Helical Nanographenes with Emission up to 1010 nm: Synthesis, Structures, and Chiroptical Properties

Perylene-Embedded Helical Nanographenes with Emission up to 1010 nm: Synthesis, Structures, and Chiroptical Properties.

Near-infrared (NIR) circularly polarized absorbing or emitting materials offer distinct advantages over their visible-light counterparts and have attracted considerable interest across various fields. Materials exhibiting NIR chiroptical properties with high fluorescence quantum yields (ΦF) are particularly rare. In this study, we report the synthesis of a series of helical nanographenes (1, 2, 3, and 4), where perylene is fused with one to four hexa-peri-hexabenzocoronene (sub)units via a strategy involving Diels-Alder cycloaddition followed by Scholl reaction. X-ray crystallographic analysis confirmed their structures, revealing helicene moieties integrated into a highly contorted framework. Benefiting from a similar distribution pattern of frontier molecular orbitals to perylene and extended π-conjugation, compounds 1-4 demonstrate respectable ΦF values of 31.9%, 15.0%, 13.7%, and 6.5%, respectively, with emission maxima reaching up to 1010 nm. Their enantiopure forms, isolated by preparative chiral HPLC, exhibit distinct circular dichroism signals and circularly polarized luminescence across a broad spectral range, extending from the ultraviolet to the NIR.

Circularly Polarized Light-Induced Chiral Growth of Achiral Plasmonic Nanoparticles Dispersed in a Solution.

Plasmonic nanoparticles (NPs) with chiral geometries have wide applications from chiral molecular sensing to enantioselective catalysis. The synthesis of chiral plasmonic nanoparticles using circularly polarized light (CPL) has attracted a considerable amount of attention because it eliminates the need for chiral molecules. However, NPs need to be immobilized on a solid substrate during synthesis. Here, we successfully synthesized colloidal chiral plasmonic NPs by depositing silver on the surface of achiral gold nanoparticles dispersed in a solution using CPL. Circular dichroism (CD) signals corresponding to the handedness of the irradiated CPL were observed when gold nanorods or gold nanotriangles were used. In contrast, no clear CD signal was observed when gold nanospheres were used. The morphological anisotropy of the gold nanoparticles was a key factor in the synthesis of chiral plasmonic nanoparticles using CPL. Furthermore, we demonstrated the tuning of chiroptical properties according to the CPL wavelength.

Can Deep Learning Search for Exceptional Chiroptical Properties? The Halogenated [6]Helicene Case.

The relationship between chemical structure and chiroptical properties is not always clearly understood. Nowadays, efforts to develop new systems with enhanced optical properties follow the trial-error method. A large number of data would allow us to obtain more robust conclusions and guide research toward molecules with practical applications. In this sense, in this work we predict the chiroptical properties of millions of halogenated [6]helicenes in terms of the rotatory strength (R). We have used DFT calculations to randomly create derivatives including from 1 to 16 halogen atoms, that were then used as a data set to train different deep neural network models. These models allow us to i) predict the Rmax for any halogenated [6]helicene with a very low computational cost, and ii) to understand the physical reasons that favour some substitutions over others. Finally, we synthesized derivatives with higher predicted Rmax obtaining excellent correlation among the values obtained experimentally and the predicted ones.

From molecules to materials: SHG-CD microscopy of structured chiral films

The interplay between molecular and structural chirality as a function of local sample morphology determines the nonlinear optical properties of many organic and hybrid organic–inorganic thin films. Here, we used second harmonic generation circular dichroism (SHG-CD) microscopy of thin molecular films of 1,1′-bi-2-naphthol (R-BINOL) as a research model. Our results show that the SHG signal measured at frequencies close to the electronic transition of BINOL molecules is resonantly enhanced by more than an order of magnitude compared to the non-resonant case. The extracted resonant SHG-CD signal is dominated by the chiral response of the molecule. In contrast, structural chirality determines the non-resonant SHG-CD images. We see clear evidence that the interference of the SHG signals caused by the molecular and structural chirality can lead to a decrease in the overall SHG intensity when both SHG signals are out of phase. These findings highlight the intricate relationship between molecular and structural chirality on the one hand and structural morphology on the other hand and pave the way for novel applications by exploiting the chiroptic properties of thin films.

Unveiling Chirality Transfer between Chiral Centers and Metal Halides in Chiral Organic-Inorganic Hybrid Metal Halides.

Chirality transfer refers to the process in which chiral cations compel the crystallization of the inorganic component into the Sohncke group. Enhancing the chirality of the inorganic component in chiral organic-inorganic hybrid metal halides (OIHMHs) through chirality transfer, aimed at improving chiroptical and spintronic properties, remains challenging due to the complexity of the underlying mechanism. To investigate this, we propose a novel concept─chirality transfer coefficient─as a means of quantifying the strength of chirality transfer in OIHMHs. A comparative study of OIHMHs with varying dimensionality, metal ions, and chiral centers was conducted to elucidate this mechanism. By analyzing factors such as hydrogen bonding, the number of chiral centers, dimensionality, helical geometry, and structural distortions, we found that chirality transfer is influenced by a combination of structural dimensions and the number of chiral centers. Importantly, our findings reveal that 0D, and 1D OIHMHs, particularly 1D with a zigzag chain configuration, exhibit stronger chirality transfer than their 2D counterparts. Moreover, in 2D OIHMHs, a reduction in the number of chiral centers enhances chirality transfer. However, no direct correlation was observed between chirality transfer and spin splitting. These insights contribute to a more comprehensive understanding of chirality transfer mechanisms and provide a strategic approach for enhancing the chirality transfer and associated physical properties in OIHMHs.

Increasing the Magnetic Transition Dipole Moment of Chiral Perovskite Through Eu3+ Doping

AbstractChiral hybrid organic‐inorganic perovskites (HOIPs) are widely investigated due to their superior chiroptical and chiral spintronic properties. Research on the enhancement of chiroptical performance is highly important for the real application of chiral HOIPs. This work employed a rare earth doping strategy to increase the magnetic transition dipole moment of chiral 2D HOIPs R‐/S‐NPB (NPB = 1‐(1‐naphthyl) ethylammonium lead bromide). Doping with Eu3+ does not change the original layered NPB microstructure, and R‐/S‐NPB‐Eu exhibited the magnetic dipole‐allowed transition luminescence of Eu3+ at 594 nm (5D0→7F1). Circular polarized luminescence (CPL) spectra combined with theoretical calculations and transient photoluminescence measurements indicated that the introduction of Eu3+ can enhance the magnetic transition dipole moment of R‐/S‐NPB, thus resulting in an unprecedented glum of 0.05. To the best of our knowledge, this is the highest value for chiral perovskite films. This work combines the unique and superior optoelectronic properties of rare‐earth ions with chiral perovskite and develops an efficient strategy to increase its anisotropy factor, which can accelerate the development of chiral optoelectronics and spintronics towards real application.