Induction of Strong and Tunable Circularly Polarized Luminescence of Nonchiral,Nonmetal, Low‐Molecular‐Weight Fluorophores Using Chiral Nanotemplates

A new strategy is described for generating strong circularly polarized luminescence with highly tunable emission bands through chiral induction in nonchiral, totally organic, low‐molecular‐weight fluorescent dyes by chiral nanotemplate systems. Our approach allows the first systematic investigation to clarify the correlation between the circular dichroism and circularly polarized luminescence intensities. As a result, a dilute solution system with the highest circularly polarized luminescence intensity achieved to date and a dissymmetry factor of over 0.1 was identified.     

Induction of Strong and Tunable Circularly Polarized Luminescence of Nonchiral,Nonmetal, Low‐Molecular‐Weight Fluorophores Using Chiral Nanotemplates

A new strategy is described for generating strong circularly polarized luminescence with highly tunable emission bands through chiral induction in nonchiral, totally organic, low‐molecular‐weight fluorescent dyes by chiral nanotemplate systems. Our approach allows the first systematic investigation to clarify the correlation between the circular dichroism and circularly polarized luminescence intensities. As a result, a dilute solution system with the highest circularly polarized luminescence intensity achieved to date and a dissymmetry factor of over 0.1 was identified.     

Fmoc-protected amino acids as luminescent and circularly polarized luminescence materials based on charge transfer interaction

Fluorenylmethyloxycarbonyl (Fmoc)-protected amino acids are effective building blocks in self-assembled architectures at hierarchical levels, which however show limited luminescent properties and chiroptical activities. Here we introduce a charge-transfer strategy to build two-component luminescent materials with emerged circularly polarized luminescence properties. A library of Fmoc-amino acids was built, which selectively form charge-transfer complexes with the electron-deficient acceptor. Embedding in amorphous polymer matrix or physical grinding could trigger the charge-transfer luminescence with adjusted wavelengths in a general manner. X-ray diffraction results suggest the multiple binding modes between donor and acceptor. And, the solution-processed coassembly could selectively exhibit circularly polarized luminescence with high dissymmetry g-factors. This work illustrates a noncovalent charge-transfer strategy to construct luminescent and chiroptical organic composites based on the easy-accessible and economic chiral N-terminal aromatic amino acids.     

Enhanced Circularly Polarized Luminescence in Emissive Charge‐Transfer Complexes

Achieving a large dissymmetry factor (g_lum) is a challenge in the field of circularly polarized luminescence (CPL). A chiral charge‐transfer (CT) system consisting of chiral electron donor and achiral electron acceptor shows bright circularly polarized emission with large g_lum value. The chiral emissive CT complexes could be fabricated through various approaches, such as grinding, crystallization, spin coating, and gelatinization, by simply blending chiral donor and achiral acceptor. The structural synergy originating from π–π stacking and strong CT interactions resulted in the long‐range ordered self‐assembly, enabling the formation of supramolecular gels. Benefiting from the large magnetic dipole transition moment in the CT state, the CPL activity of CT complexes exhibited large circular polarization. Our design strategy of the chiral emissive CT complexes is expected to help the development of new molecular engineering strategies for designing highly efficient CPL‐active materials.     

Chiroptical Helices of N‐Terminal Aryl Amino Acids through Orthogonal Noncovalent Interactions

In the solid state, amino acids (alanine and phenylglycine) with appended pyrene segments self‐assembled into α‐helix‐like structures by asymmetrical H‐bonds between carboxylic acid and amide segments, further inducing supramolecular tilted chirality of the achiral pyrenes. These structures bind melamine and electron‐deficient units through H‐bond and charge‐transfer interactions, respectively. Charge‐transfer interactions enhance the dissymmetry g‐factor of absorption (g_abs; up to 1.4×10^?2) with an extended Cotton effect active region (from 250 to 600 nm). Incorporating melamine inverts the handedness of circularly polarized luminescence and boosts the dissymmetry g‐factor (g_lum). Melamine also induces macroscopic chirality at the nanoscale, whereby the 2D lamellar structures are transformed into 1D helices at the nanoscale, leading to giant tubular structures at the microscale.     

Enhanced Circularly Polarized Luminescence from Reorganized Chiral Emitters on the Skeleton of a Zeolitic Imidazolate Framework

A chiral zeolitic imidazolate framework (ZIF) showing circularly polarized luminescence (CPL) has been successfully constructed by blending binapthyl‐derived chiral emitters with ZIF‐8 rhombic dodecahedron nanoparticles. This approach solves a major trade‐off in CPL‐active materials: the large luminescence dissymmetry factor (g_lum) always suffers from suppression of luminescence efficiency. Compared to the optical properties of chiral emitters, the obtained chiral ZIF nanomaterials showed an enhanced fluorescence efficiency while the |g_lum| value is significantly amplified by one order of magnitude. Additionally, enantioselective fluorescence sensing in response to α‐hydroxycarboxylic acids has been enhanced in chiral ZIFs. Reorganization and conjunction of chiral emitters to the skeleton of ZIF nanoparticles can greatly improve both the luminescence quantum yield and circularly polarization, which facilitates the design of more efficient chiroptical materials.     

Chiroptical coassemblies between organic carboxylic acids and amino acid derivatives with C3-symmetry

Benzimidazole amino acid derivatives behave as supramolecular hosts to include organic acids via complementary hydrogen bonding whereby supramolecular chirality and chiroptical properties could be manipulated. Organic acids enhanced the chiral assembly that showed tunable circularly polarized luminescence with high dissymmetry g-factors at 10⁻² grade.     

Tunable Excimer Circularly Polarized Luminescence in Isohexide Derivatives from Renewable Resources

Organic compounds showing circularly polarized luminescence (CPL) are at the forefront of novel applications and technologies. Here we show the synthesis and chiroptical properties of pyrene and perylene derivatives of inexpensive chiral scaffolds: isomannide and isosorbide. Low-intensity ECD spectra were obtained, suggesting the absence of chromophore interaction in the ground state, except in the case of isomannide bis-perylenecarboxylate, whose ECD spectrum showed a positive exciton couplet. All isomannide derivatives, with the only exception of the one containing a pyrenecarboxylate and a perylenecarboxylate, exhibited excimer CPL spectra, whereas isosorbide derivatives did not show any CPL. Isomannide derivatives bearing two pyrenecarboxylate or two pyrenylacetate groups showed positive CPL emission with dissymmetry factors up to 10⁻², which depends on the conformational freedom of the appended units. The CPL sign, Stokes shift and order of magnitude of dissymmetry factor were reproduced by excited-state calculations on a representative compound. Interestingly, the mixed derivative containing pyrenic units with different spacing from the isomannide scaffold showed an oppositely signed excimer band with respect to the homo-substituted derivatives.     

Planar‐Chiral Through‐Space Conjugated Oligomers: Synthesis and Characterization of Chiroptical Properties

Optically active through‐space conjugated oligomers, namely, a dimer, trimer, tetramer, and cyclic trimer, consisting of a planar‐chiral [2.2]paracyclophane skeleton were synthesized. In the ground state, observed similarities in the chiroptical properties of the oligomers were attributed to the equivalent orientations of two adjacent chromophores. In the excited state, the oligomers were folded into a form analogous to a one‐handed helix by photoexcitation. All the compounds in dispersed solution exhibited intense circularly polarized luminescence with relatively large anisotropy factors on the order of 10^?3.     

Biomimetic Chiral Photonic Crystals

Although it is well known that the amazing iridescent colors of the cuticle of beetles reflect the intricate nanoscale organization of bio‐fibers, artificial inorganic materials with comparable optical responses have not yet been synthesized from abiotic nanoscale building blocks. Such materials could find broad applications, including in circular polarizers, to generate circularly polarized luminescence, or in lasers. Herein, we describe a general method for the fabrication of biomimetic chiral photonic crystals by Langmuir–Schaefer assembly of colloidal inorganic nanowires. We not only reproduced the intricate helical structure and circularly polarized color reflection observed in beetles, but also achieved the highest chiroptical activity with a dissymmetry factor of ?1.6 ever reported for chiral inorganic nanostructures. More importantly, the programmable structural control based on the precise interlayer arrangement endows us with unprecedented freedom to manipulate the optical activity of as‐fabricated chiral photonic crystals.     

Dual Upconverted and Downconverted Circularly Polarized Luminescence in Donor–Acceptor Assemblies

Through mimicking both the chiral and energy transfer in an artificial self‐assembled system, not only was chiral transfer realized but also a dual upconverted and downconverted energy transfer system was created that emit circularly polarized luminescence. The individual chiral π‐gelator can self‐assemble into a nanofiber exhibiting supramolecular chirality and circularly polarized luminescence (CPL). In the presence of an achiral sensitizer Pd^II octaethylporphyrin derivative, both chirality transfer from chiral gelator to achiral sensitizer and triplet‐triplet energy transfer from excited sensitizer to chiral gelator could be realized. Upconverted CPL could be observed through a triplet–triplet annihilation photon upconversion (TTA‐UC), while downconverted CPL could be obtained from chirality‐transfer‐induced emission of the achiral sensitizer. The interplay between chiral energy acceptor and achiral sensitizer promoted the communication of chiral and excited energy information.     

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

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

Circularly polarized luminescence from bridged triarylamine helicenes

The first examples of circularly polarized luminescence from chiral bridged triarylamine-based heterohelicene molecules are reported. The luminescence dissymmetry factors are approximately |0.001|.     

Self‐Assembled Luminescent Quantum Dots To Generate Full‐Color and White Circularly Polarized Light

The design and fabrication of quantum dots (QDs) with circularly polarized luminescence (CPL) has been a great challenge in developing chiroptical materials. We herein propose an alternative to the use of chiral capping reagents on QDs for the fabrication of CPL‐active QDs that is based on the supramolecular self‐assembly of achiral QDs with chiral gelators. Full‐color‐tunable CPL‐active QDs were obtained by simple mixing or gelation of a chiral gelator and achiral 3‐mercaptopropionic acid capped QDs. In addition, the handedness of the CPL can be controlled by the supramolecular chirality of the gels. Moreover, QDs with circularly polarized white light emission were fabricated for the first time by tuning the blending ratio of colorful QDs in the gel. The chirality transfer in the co‐assembly of the achiral QDs with the gelator and the spacer effect of the capping reagents on the QD surface are also discussed. This work provides new insight into the design of functional chiroptical materials.     

Integrating Achiral and Chiral Organic Ligands in Zero-Dimensional Hybrid Metal Halides to Boost Circularly Polarized Luminescence

Chiral zero-dimensional hybrid metal halides (0D HMHs) could combine excellent optical properties and chirality, making them promising for circularly polarized luminescence (CPL). However, chiral 0D HMHs with efficient CPL have been rarely reported. Here, we propose an efficient strategy to achieve simultaneously high photoluminescence quantum yield (PLQY) and large dissymmetry factor (g_lum), by integrating achiral and chiral ligands into 0D HMHs. Specifically, three pairs of chiral 0D hybrid indium-antimony chlorides are synthesized by combing achiral guanidine with three types of chiral methylbenzylammonium-based derivatives as the organic cations. These chiral 0D HMHs exhibit near-unity PLQY and large g_lum values up to around ±1×10⁻². The achiral guanidine ligand is not only essential to crystallize these hybrid indium-antimony chlorides to achieve near-unity PLQYs, but also greatly enhances the chirality induction from organic ligands to inorganic units in these 0D HMHs. Furthermore, the choice of different chiral ligands can modify the strength of hydrogen bonding interactions in these 0D HMHs, to maximize their g_lum values. Overall, this study provides a robust way to realize efficient CPL in chiral HMHs, expanding their applications in chiroptical fields.     

Strong Coupling of Chiral Frenkel Exciton for Intense,Bisignate Circularly Polarized Luminescence

We show that chiral Frenkel excitons yield intense circularly polarized luminescence with an intrinsic dissymmetry factor in emission g_lum as high as 0.08. This outstanding value is measured through thin films of cyanine J-aggregates that form twisted bundles. Our measurements, obtained by a Mueller polarization analysis, are artifact-free and reveal a quasi-perfect correlation between the dissymmetry factors in absorption, g_abs, and in emission g_lum. We interpret the bisignate dissymmetry factors as the signature of a strong coupling between chiral Frenkel excitons longitudinally excited along the bundles. We further resolve by polarimetry analysis the split in energy between the excited states with a Davydov splitting as small as 28 meV. We finally show the anti-Kasha nature of the chiral emission bands with opposite optical chirality. These mirror-imaged emissive chiroptical features emerge from the structural rigidity of the bundles that preserves the ground- and excited-state chirality.     

A Smart Sensing Method for Object Identification Using Circularly Polarized Luminescence from Coordination‐Driven Self‐Assembly

The potential use of circularly polarized luminescence for object identification in a sensor application is demonstrated. New luminescence probes using pyrene derivatives as sensor luminophores were developed. (R,R)‐Im₂Py and (S,S)‐Im₂Py contain two chiral imidazole moieties at 1,6‐positions through ethynyl spacers (angle between spacers ca. 180°). The probe molecules spontaneously self‐assemble into chiral stacks (P or M helicity) upon coordination to metal ions with tetrahedral coordination (Zn²⁺). The chiral probes display neither circular dichroism (CD) nor circularly polarized luminescence (CPL) without metal ions. However, (R,R)‐Im₂Py and (S,S)‐Im₂Py exhibit intense chiroptical activity (CD and CPL) upon self‐assembly with Zn²⁺ ions. (R,R)‐Im₂Py and (S,S)‐Im₂Py with chemical stimuli‐responsibility allow sensing using the CPL signal as detection output, enabling us to discriminate between a signal from the target analyte and that from non‐target species.     

New Types of Planar Chiral [2.2]Paracyclophanes and Construction of One‐Handed Double Helices

New types of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes were synthesized from racemic 4,12‐dihydroxy[2.2]paracyclophane as the starting compound. Regioselective dibromination and transformation afforded a series of planar chiral (R_p)‐ and (S_p)‐4,7,12,15‐tetrasubstituted [2.2]paracyclophanes, which can be used as chiral building blocks. In this study, left‐ and right‐handed double helical structures were constructed via chemoselective Sonogashira–Hagihara coupling. The double helical compounds were excellent circularly polarized luminescence (CPL) emitters with large molar extinction coefficients, good photoluminescence quantum efficiencies, and large CPL dissymmetry factors.     

Azahelicene‐Fused BODIPY Analogues Showing Circularly Polarized Luminescence

Helical carbazole‐based BODIPY analogues were readily synthesized via aza[7]helicenes. The structures of azahelicene‐incorporated BF₂ dyes were elucidated by x‐ray diffraction analysis. DFT calculations revealed that the π‐conjugated system expanded from the helicene moiety to the BODIPY framework. The azahelicene‐fused boron complexes showed the Cotton effects and the circularly polarized luminescence (CPL) in the visible region. Furthermore, an axially chiral binaphthyl group was attached to the helically chiral dyes, which enhanced the chiroptical properties.     

Yellow Circularly Polarized Luminescence from C1‐Symmetrical Copper(I) Complexes

The synthesis of chiral C₁‐symmetrical copper(I) complexes supported by chiral carbene ligands is described. These complexes are yellow emitters with modest quantum yields. Circularly polarized luminescence (CPL) spectra show a polarized emission band with dissymmetry factors |g_lum|=1.2×10^?3. These complexes are the first reported examples of molecular copper(I) complexes exhibiting circularly polarized luminescence. In contrast with most CPL‐emitting molecules, which possess either helical or axial chirality, the results presented show that simple chiral architectures are suitable for CPL emission and unlock new synthetic possibilities.