Tuning the (Chir)Optical Properties and Squeezing out the Inherent Chirality in Polyphenylene-Locked Helical Carbon Nanorings

Distorting linear polyaromatic hydrocarbons (PAHs) out of planarity affects their physical properties and breaks their symmetry to induce inherent chirality. However, the chirality cannot be achieved in large distorted PAHs-based macrocycles due to a low racemization barrier for isomerization. Herein, we report the precise synthesis and tuning size-dependent (chir)optical properties of a new class of chiral PAHs-containing conjugated macrocycles (cyclo[n]paraphenylene-2,6-anthrylene, [n]CPPAn_2,6 ; n=6–8). Their inherent chiralities were squeezed out in small anthrylene-based macrocycles. Efficient resolutions for chiral enantiomers with (P)/(M)-helicity of small [6-7]CPPAn s were achieved by HPLC. Interestingly, these macrocycles showed enriched size-dependent physical, chiral, and (chir)optical properties. Theoretical calculations indicate that these macrocycles have high strain energy (E_strain=60.8 to 73.4 kcal/mol) and very small E_gap (∼3.0 eV). Notably, these enantiomers showed strong chiroptical properties and dissymmetry factors (|g_abs| and |g_lum|∼0.01 for an enantiomer of [6]CPPAn_2,6 ), which can give them potential applications in optically active materials.     

Intense Molar Circular Dichroism in Fully Conjugated All-Carbon Macrocyclic 1,3-Butadiyne Linked pseudo-meta [2.2]Paracyclophanes**

The synthetic access to macrocyclic molecular topologies with interesting photophysical properties has greatly improved thanks to the successful implementation of organic and inorganic corner units. Based on recent reports, we realized that pseudo-meta [2.2]paracyclophanes (PCPs) might serve as optimal corner units for constructing 3D functional materials, owing to their efficient electronic communication, angled substituents and planar chirality. Herein, we report the synthesis, characterization and optical properties of four novel all-carbon enantiopure macrocycles bearing three to six pseudo-meta PCPs linked by 1,3-butadiyne units. The macrocycles were obtained by a single step from enantiopure, literature-known dialkyne pseudo-meta PCP and were unambiguously identified and characterized by state of the art spectroscopic methods and in part even by x-ray crystallography. By comparing the optical properties to relevant reference compounds, it is shown that the pseudo-meta PCP subunit effectively elongates the conjugated system throughout the macrocyclic backbone, such that already the smallest macrocycle consisting of only three subunits reaches a polymer-like conjugation length. Additionally, it is shown that the chiral pseudo-meta PCPs induce a remarkable chiroptical response in the respective macrocycles, reaching unprecedented high molar circular dichroism values for all-carbon macrocycles of up to 1307 L mol⁻¹ cm⁻¹.     

Luminescent Chiral Exciplexes with Sky-Blue and Green Circularly Polarized-Thermally Activated Delayed Fluorescence

Luminescent exciplexes based on a chiral electron donor and achiral acceptors are reported as a new approach to design circularly polarized (CP) and thermally activated delayed fluorescence (TADF) emitters. This strategy results in rather high CP luminescence (CPL) values with g_lum up to 7×10⁻³, one order of magnitude higher in comparison to the CPL signal recorded for the chiral donor alone (g_lum ∼7×10⁻⁴). This increase occurs concomitantly with a CPL sign inversion, as a result of the strong charge-transfer emission character, as experimentally and theoretically rationalized by using a covalent chiral donor-acceptor model. Interestingly, blue, green-yellow and red chiral luminescent exciplexes can be obtained by modifying with the electron accepting character of the achiral unit while keeping the same chiral donor unit. These results bring new (inter)molecular guidelines to obtain simply and efficiently multi-color CP-TADF emitters.     

Synthesis of Highly Luminescent Chiral Nanographene

Chiral nanographenes with both high fluorescence quantum yields (Φ_F) and large dissymmetry factors (g_lum) are essential to the development of circularly polarized luminescence (CPL) materials. However, most studies have been focused on the improvement of g_lum, whereas how to design highly emissive chiral nanographenes is still unclear. In this work, we propose a new design strategy to achieve chiral nanographenes with high Φ_F by helical π-extension of strongly luminescent chromophores while maintaining the frontier molecular orbital (FMO) distribution pattern. Chiral nanographene with perylene as the core and two dibenzo[6]helicene fragments as the wings has been synthesized, which exhibits a record high Φ_F of 93 % among the reported chiral nanographenes and excellent CPL brightness (B_CPL) of 32 M⁻¹ cm⁻¹.     

A Chiral Emissive Conjugated Corral for High-Affinity and Highly Enantioselective Recognition in Water

Accurately distinguishing between enantiomeric molecules is a fundamental challenge in the field of chemistry. However, there is still significant room for improvement in both the enantiomeric selectivity (K_R(S)/K_S(R)) and binding strength of most reported macrocyclic chiral receptors to meet the demands of practical application scenarios. Herein, we synthesized a water-soluble conjugated tubular host—namely, corral[4]BINOL—using a chiral 1,1′-bi-2-naphthol (BINOL) derivative as the repeating unit. The conjugated chiral backbone endows corral[4]BINOL with good fluorescent emission (QY=34 % ) and circularly polarized luminescence (|g_lum| up to 1.4×10⁻³) in water. Notably, corral[4]BINOL exhibits high recognition affinity up to 8.6×10¹⁰ M⁻¹ towards achiral guests in water, and manifested excellent enantioselectivity up to 18.7 towards chiral substrates, both of which represent the highest values observed among chiral macrocycles in aqueous solution. The ultrastrong binding strength, outstanding enantioselectivity, and facile accessibility, together with the superior fluorescent and chiroptical properties, endow corral[4]BINOL with great potential for a wide range of applications.     

Helical β-isoindigo-Based Chromophores with B−O−B Bridge: Facile Synthesis and Tunable Near-Infrared Circularly Polarized Luminescence

It is essential to create organic compounds that exhibit circularly polarized luminescence (CPL) in the near-infrared (NIR) range. Helicene-type emitters possess appealing chiroptical features, however, such NIR molecules are scarce due to a paucity of synthetic strategies. Herein, we developed a series of helical β-isoindigo-based B−O−B bridged aza-BODIPY analogs that were synthesized conveniently. The reaction of diimino-β-isoindigo with a heteroaromatic amine produced a restricted ligand cavity, which triggered off the generation of a B−O−B bridge. The B−O−B bridge led to distorted conformations that satisfy the helical requirements, resulting in excellent spectroscopic and chiroptical properties. Tunable CPL with the highest luminescence dissymmetry factor (g_lum) of 1.3×10⁻³ and a CPL brightness (B_CPL=11.5 M⁻¹ cm⁻¹) in the NIR region was achieved. This synthetic approach is expected to offer a new opportunity to chiral chemistry and increase flexibility for chiroptical tuning.     

Helical Oligophenylene Linked with [2.2]Paracyclophane: Stereogenic π-Conjugated Dye for Highly Emissive Chiroptical Properties

A stereogenic π-system based on dimer ( 2 ) and trimer ( 3 ) of [2.2]paracyclophane (PC) and biphenyl was prepared and its structural, photophysical, and chiroptical properties were investigated. X-ray analysis revealed that the quaterphenyl moieties in 2 adopt a double helical structure anchoring [2.2]PC from both sides. Furthermore, 3 forms a isosceles triangle structure with a large chiral cavity. A homodesmotic reaction using DFT calculations revealed that 2 has a larger strain energy than 3 owing to its highly twisted phenylene linkers. Electronic and circular dichroic (CD) spectra were recorded in CH₂Cl₂ solution. The spectra of both 2 and 3 are similar, and their longest absorption band accompanying a remarkable Cotton effect is attributed to the transition from HOMO to LUMO, which is delocalized to the quaterphenyl moiety. These compounds exhibit fairly high fluorescence quantum yields (ϕ=0.70–0.83) and moderate dissymmetry factor (|g_CPL|=1.6×10⁻³) in circularly polarized luminescence (CPL).     

Turn-on Circularly Polarized Luminescence in Chiral Indium Chlorides by 5s2 Metal Centers

Introducing chirality into the metal-halide hybrids has enabled many emerging properties including chiroptical activity, spin-dependent transport, and ferroelectricity. However, most of the chiral metal-halide hybrids to date are non-emissive, and the underlying mechanism remains elusive. Here, we show a new strategy to turn on the circularly polarized luminescence (CPL) in chiral metal-halide hybrids. We demonstrate that alloying Sb³⁺ into chiral indium-chloride hybrids dramatically increases the photoluminescence quantum yield in two new series of chiral indium-antimony chlorides. These materials exhibit strong CPL signals with tunable energy and a high dissymmetry factor up to 1.5×10⁻². Mechanistic studies reveal that the emission originates from the self-trapped excitons centered in 5s² Sb³⁺. Moreover, near-ultraviolet pumped white light is demonstrated with a polarization up to 6.0 %. Our work demonstrates new strategies towards highly luminescent chiral metal-halide hybrids.     

Oxidation of an Internal-Edge-Substituted [5]Helicene-Derived Phosphine Synchronously Enhances Circularly Polarized Luminescence

Small chiral organic molecules with CD properties are in high demanded due to their potential use in promising electronic and biological applications. Herein, we reveal a system in which the oxidation of a phosphino group to the corresponding phosphine oxide on the inner rim of a helicene derivative induces a CPL response. Laterally π-extended 7,8-dihydro[5]helicenes bearing phosphine and phosphine oxide groups on their inner helical rims (i. e., the C1 position) were synthesized, and their helical structures were unambiguously determined by X-ray crystallography. The photophysical (UV/visible and emission) and chiroptical properties of these compounds were investigated in various solvents. Despite their structural similarities, phosphine oxide showed a significantly better CPL response than phosphine, with a high dissymmetry factor for emission (|g_lum|=(1.3–1.9)×10⁻³) that can be attributed to structural changes in the interior of the helicene helix.     

Synthesis of i-Corona[6]arenes for Selective Anion Binding: Interdependent and Synergistic Anion–π and Hydrogen-Bond Interactions

i-Corona[3]arene[3]tetrazines were synthesized from the nucleophilic aromatic substitution reaction of resorcinol and its derivatives with 3,6-dichlorotetrazine in a one-pot fashion under mild conditions. All of the resulting macrocycles adopted 1,3,5-alternate conformation irrespective of the nature of the substituents on both upper- and lower-rims. i-Corona[3]arene[3]tetrazine was found to self-regulate its macrocyclic conformation and cavity to recognize anions with binding constants spanning from 26 M⁻¹ to 2.2×10³ M⁻¹ depending on the structure of the anions. The selective binding resulted from a significant interdependent and synergistic effect between multiple tetrazine π/anion and C_aryl–H/anion hydrogen bond interactions. Taking advantage of synergistic effect revealed, a cyanobenzene-embedded i-corona[3]arene[3]tetrazine was designedly synthesized and highly selective and very strong affinity toward nitrate with a binding constant of 2.2×10⁵ M⁻¹ was achieved.     

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.     

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.     

Cyclobishelicenes: Shape-Persistent Figure-Eight Aromatic Molecules with Promising Chiroptical Properties

Cyclobis[n]helicenes (n=3 or 5) are chiral D₂-symmetric π-conjugated macrocycles with stable lemniscular, or figure-eight, shapes. The conformational analysis of five different cyclobis[n]helicenes revealed that these molecules can only exist as their lemniscular conformers with high barriers to enantiomerization (>200 kJ mol⁻¹). The enantiomers of a cyclobis[5]helicene were resolved by HPLC and their unusual chiroptical properties were attributed to the inherent chirality of their macrocyclic figure-eight.     

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.     

Amino-Acid-Induced Circular Polarized Luminescence in One-Dimensional Manganese(II) Halide Hybrid

Circular polarized luminescence (CPL)-active materials attract great attentions owing to their widely applications in 3D optical displays and encrypted transmission. Inspired by the strategies adopted in perovskite based CPL materials, herein, CPL-active hybrids (D)- and (L)-(tert-butyl prolinate)MnCl₃ were successfully prepared by assembling chiral D/L tert-butyl prolinate with manganese (II) chloride. Single crystal structures show the as-formed hybrids possess one-dimensional (1D) structure containing linear chains of face-sharing MnCl₆ octahedral surrounded by prolinate cations. The 1D Mn(II) hybrids display strong red emission peaked at 646 nm with PLQY of 67.1 % and 57.2 % for d -type and l -type, respectively, representing the highest PLQY for 1D Mn^II hybrids. Interestingly, the 1D Mn(II) hybrids exhibit prominent circular dichroism (CD) signals and remarkable CPL activity with the dissymmetry factor g of 6.1*10⁻³ and −6.3*10⁻³ from 550 to 800 nm for (D)- and (L)-(tert-butyl prolinate)MnCl₃, respectively, owing to the existence of chiral cations. It is worthy noted the obtained g represents the highest value for non-lead organic–inorganic hybrids.     

Circularly polarized luminescence induced by excimer based on pyrene-modified binaphthol

A new chiral bromobinaphthol-pyrene compound was developed to achieve a green circularly polarized luminescence (CPL) from its excimer with a dissymmetry factor (|g_lum|) value of 4.3 × 10⁻³ and a high quantum yield Φ_{F, solid} up to 55.9%, while no CPL signals could be observed for the blue luminescence from unimolecule. Meanwhile, reversal CPL signals can be observed from both concentrated solution and solid     

Rhodium-Catalyzed Enantioselective Synthesis of Highly Fluorescent and CPL-Active Dispiroindeno[2,1-c]fluorenes

The enantioselective synthesis of chiral [7]-helical dispirodihydro[2,1-c]indenofluorenes (DSF-IFs) was achieved for the first time in good yields with high er values (er up to 99 : 1). The crucial step of the whole reaction sequence was the enantioselective intramolecular [2+2+2] cycloaddition of tethered triynediols to indenofluorenediols, which was catalyzed by a Rh/SEGPHOS® complex. Further transformations led to the corresponding DSF-IFs. The prepared helically chiral DSF-IFs combine circularly polarized luminescence (CPL) activity (g_lum=∼10⁻³) with exceptionally high fluorescence quantum yields (up to Φ_lum=0.97).     

Control of Axial Chirality by Planar Chirality Based on Optically Active [2.2]Paracyclophane

Optically active X-shaped molecules based on the planar chiral [2.2]paracyclophane building block were prepared, in which di(methoxy)terphenyl units were stacked on the central benzene rings. At 25 °C, anisolyl rings freely rotate in solution, while in the crystal form, they are fixed by intramolecular CH–π interactions, thereby leading to the expression of the axial chirality, i.e., propeller chirality was exhibited by the planar chiral [2.2]paracyclophane moiety. The X-shaped molecule exhibited good circularly polarized luminescence (CPL) profiles with moderate Φ_PL and a large g_lum value in the order of 10⁻³ at 25 °C, in solution. In contrast, at −120 °C, dual CPL emission with opposite signs was observed. According to the theoretical studies, the rotary motion of the anisolyl units is suppressed in the excited states, and so emission from two isomers could be observed. These results demonstrate that the axial chirality was controlled by the planar chirality, leading ultimately to propeller chirality.     

Aggregation-Induced Circularly Polarized Luminescence from Boron Complexes with a Carbazolyl Schiff Base

A variety of carbazolyl-appended Schiff bases were readily synthesized from 1-formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole-based BODIPY analogues showing solid-state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et₂AlCl-mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation-induced fluorescence and circularly polarized luminescence (CPL) with the Φ_F and g_lum of up to 0.22 and −3.5×10⁻³, respectively, in the solid state. The solid-state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations.     

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.