Synthesis of π-Conjugated Chiral Organoborane Macrocycles with Blue to Near-Infrared Emissions and the Diradical Character of Cations

Crystalline, Porous Figure-Eight-Noded Covalent Organic Frameworks

Figure-eight macrocycles represent a fascinating class of π-conjugated units characterized by unique aesthetics and non-contact molecular crossing at the center. Despite progress in synthesis over the past century, research into inorganic, organic, and polymeric figure-eight materials remains in its infancy. Here we report the first examples of figure-eight covalent organic frameworks by condensing figure-eight knots to create extended porous figure-eight π architectures. A distinct feature is that polymerization interweaves figure-eight knots into double-decker layers, which upon supramolecular polymerization organize well-defined layer frameworks. The figure-eight frameworks exhibit a band gap of 2.3 eV and emit bright orange florescence with benchmark quantum yields. Remarkably, the donor-acceptor figure-eight skeletons convert the figure-eight knots into reduction centers and the linkers into oxidation sites upon light irradiation, enable charge transport and accumulation through π columns, while the built-in hydrophilic micropores allow rapid water and oxygen delivery via capillary effect. With these distinct features, the figure-eight frameworks function as a photocatalyst to produce hydrogen peroxide at high rate and efficiency with water/saltwater, oxygen/air, and light as sole inputs. This work paves a way to a new class of molecular frameworks, underpinning the study of well-defined figure-eight materials to explore unprecedented structures and functions so far we untouched.

Boraporphyrins: Unlocking Global Aromaticity in Organoboron Macrocycles

We report the synthesis of 5-bora-21,22-dioxaporphyrin 5 and its main-group and d-block metal complexes 6 and 7, respectively. These macrocyclic boranes constitute the first examples of neutral porphyrins with boron in a meso-position that exhibit global aromaticity. This is evidenced by spectroscopic and structural features as well as calculated nucleus independent chemical shifts (NICS) and anisotropic induced current densities (ACID). The boraporphyrins absorb light strongly in the red spectral region (Q bands) and show enhanced fluorescence with higher quantum yields (5: 29%) compared to conventional porphyrins. DFT calculations reveal that the incorporation of the borane moiety has a distinct impact on the frontier orbital energies, thus leading to altered electrochemical and optical properties.

Brightening Up Circularly Polarized Luminescence of [6]Helicenes by Fusion with BN-Heterocycles

We here disclose synthesis and properties of a series of BN-heterocycle-fused [6]helicenes. The fusion of the BN-heterocycle is helpful to extend π-conjugation and increase absorptivity and fluorescence efficiency of the first excited state. Especially, the double [6]helicene BiBN-BiHC shows outstanding circularly polarized luminescence performance with BCPL up to 49.0 M-1 cm-1, owing to its very high ΦF (0.87), large ε (5.47 × 104 M-1 cm-1), and fairly good |glum| (2.06 × 10-3).

Advances in Chiral Macrocycles: Molecular Design and Applications

Chiral macrocycles have recently emerged as promising materials for enantioselective recognition, asymmetric catalysis, and circularly polarized luminescence (CPL) due to their terminal-free structure, preorganized chiral cavities, and unique host-guest and self-assembly properties. This review summarizes recent advances in the design and synthesis of chiral macrocycles with central, axial, helical, and planar chirality, each imparting distinct structural and chiroptical characteristics. We highlight key strategies for constructing these macrocycles and their applications in optoelectronic and catalytic systems. Emphasis is placed on the balance between rigidity and flexibility in macrocycle design, essential for effective molecular recognition, adaptable catalysis, and CPL. We conclude with perspectives on future opportunities, anticipating ongoing developments in chiral macrocycle research.

Hyperconjugation Engineering of π-Extended Azaphosphinines for Designing Tunable Thermally Activated Delayed Fluorescence Emitters

Implanting heteroatoms into organic π-conjugated molecules (OCMS) offered a great opportunity to fine-tune the chemical structures and optoelectronic properties. This work describes a new family of 1,4-azaphosphinines with extended σ-π hyperconjugations. The photophysical studies revealed that azaphosphinines exhibited narrow-band thermally activated delayed fluorescence (TADF) ( full width at half-maximum: 26-40 nm). According to the orbital localization analysis and natural bond orbital analysis, the effective σ*-π* hyperconjugation is believed to induce the multiple-resonance (MR) TADF, which is distinct from the p-π conjugation-induced MR-TADF in BN systems. Although having the large ΔES1-T1s (>3.0 ev), the study suggested that σ*-π hyperconjugation endowed the system with the structural vibration favorable for the spin-vibronic-assisted RISC. Having the tunable p-centers (lp, O, S, Se, and Me+), azaphosphinines showed a fine-tuned TADF. Generally, azaphosphinines with strong σ*-π* hyperconjugations showed small ΔES1-T1s, efficient RISCs, and high PLQYs. Leveraging on the efficient hyperconjugations, TADF emission of the system spanned from UV-blue to green. Particularly, extended azaphosphinines exhibited the high photoluminescence quantum yields (74% in toluene and 92% in the 10% doped PMMA). As a proof of concept, two azaphosphinines with a PO center were applied as the light-emitting materials in organic lighting-emitting diodes. The devices showed the narrow-band UV- and deep-blue emission with EQE as high as 10.3%. The current study offered us a new strategy, namely, σ-π hyperconjugation-induced MR-TADF, for designing OCMs with tunable light-emitting properties.

[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.

Rational Design of Crystalline and Enantiomerically Pure Helicenes with Open-Shell Singlet Ground States

Helicene diradical derivatives have attracted widespread attentions because of their unique magnetic and chiroptoelectronic properties, however, crystalline and enantiomerically pure forms of helicene diradicals are extremely rare. Herein, we describe the rational design and synthesis of o-quinone functionalized helicene diradicals with crystalline enantiomerical purity. Diradical dianion salt Rac-3K and its enantiomers P/M-3K were obtained by reduction of corresponding precursors Rac-3 and P/M-3 with two equivalent potassium graphite in THF in the presence of (di)benzo-18-crown-6. Neutral dioxoborocyclic helicene diradicals (Rac-3B and P/M-3B) were produced by reactions of Rac-3 or P/M-3 with chlorobis(perfluorophenyl)borane (B(C6F5)2Cl. Crystal structures of compounds Rac-3K, Rac-3B and P/M-3K were obtained by single crystal X-ray diffraction. Their open-shell singlet state ground states were confirmed by electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) measurements and theoretical calculations. Their chiroptical properties were investigated by the electronic circular dichroism (ECD) spectroscopy. This work provides the first examples of enantiopure helicene diradical dianions and boron-containing helicene diradicals.

Enantiopure Macrocycles Based on Tröger's Base and Diphenyl Maleimide Exhibiting Strong Chiral Emission and Host-Guest Properties

While a plenty of macrocyclic hosts have been developed in supramolecular chemistry, those that combine chiral luminescent properties and host-guest recognition abilities are still uncommon. Herein, two pairs of enantiomeric macrocycles were synthesized via Suzuki-Miyaura [2+2] cyclization reactions using Tröger's base and diphenyl maleimide as the building blocks. The diphenyl maleimide units impart these macrocycles with highly strong fluorescence, achieving quantum yields up to 100 % in apolar solvents. Furthermore, the chiral, V-shaped Tröger's base units provide the macrocycles with circularly polarized luminescence (|glum|=1.68×10-3) and well-define cavity for hosting electron-deficient or positively charged guests with Ka up to 1.7×106 M-1.

Recent Advances in NIR-Switchable Multi-Redox Systems Based on Organic Molecules

Electrochromic systems capable of switching absorption in the near-infrared (NIR) region (750-2500 nm) are attractive from the viewpoint of applications for material and life science, and thus several examples have been reported to date. In general, the development of organic-based systems is needed to reduce the environmental impact and improve biocompatibility. Although extending the switchable spectral range is crucial for the application of organic electrochromic molecules, the switching of NIR absorption based on redox interconversion is still a challenging issue regarding reversibility and durability during interconversion. To overcome this potential instability, the introduction of heteroatoms into the molecular backbone and/or π-extension could be useful strategies in terms of effective delocalization of charge and spin in the corresponding redox states. In this review, we focus on redox-active well-defined small molecules that enable ON/OFF switching of NIR absorption based on precise control of the redox states, and present recent studies on their intrinsic electrochemical and spectroscopic properties and/or structural characterization of their charged states.

Photo-Induced Radical Generation of Supramolecular Gel with Sign-Inverted and White-Light Circularly Polarized Luminescence

The realization of persistent luminescence and in particular circularly polarized luminescence (CPL) of organic radicals remains a challenge due to their sensitivity to oxygen at ambient conditions and elusive excited state chirality control. Here, it is reported that UV-irradiation on a supramolecular gel from a chiral triarylamine derivative, TPA-Ala, led to the formation of luminescent radicals with bright CPL. TPA-Ala can form an organogel in chloroform with blue emission and supramolecular chirality as demonstrated by both CD and CPL signals. Upon UV 365 nm irradiation, an emission color change from blue to cyan is observed due to the formation of photo-induced radicals. Interestingly, it is found that the supramolecular gel radicals showed stable luminescence with a lifetime ≈ 10 days in dark environments and inverted CPL, which represents a scarce example with persistent CPL from doublet-state due to oxygen isolation ability of the gel network. Furthermore, doping a guest dye, Rhodamine B (RhB), into the supramolecular gel (RhB/TPA-Ala = 30% in molar ratio) successfully obtained a transient white-light CPL through the superposition of photo-induced radical and guest dye emissions. This work provides a useful methodology for the fabrication of radical-based CPL materials via a supramolecular assembly approach.

Boat-to-boat conformation inversions of cyclobis[7,8-(para-quinodimethane)-3,7-(9-(p-tolyl)-9H-carbazole)] in the neutral and tetracationic state

We report the synthesis of macrocyclic cyclobis[7,8-(para-quinodimethane)-3,7-(9-(p-tolyl)-9H-carbazole)] CBQCz. We found that CBQCz showed temperature-dependent and four-electron oxidative conformation changes. Both CBQCz and CBQCz4+ possess boat-to-boat conformation inversions. The smaller inverted energy and less curved structure of CBQCz4+ are due to the conjugated effect of tetracations.

The Effects of Pore Defects in π-Extended Pentadecabenzo[9]helicene

The introduction of precise pore defects into nanocarbon structures results in the emergence of distinct physicochemical characteristics. However, there is a lack of research on non-planar chiral nanographene involving precise pore defects. Herein, we have developed two analogues to the π-extended pentadecabenzo[9]helicene (EP9H) containing embedded pore defects. Each molecules, namely extended dodecabenzo[7]helicene (ED7H; 1) or extended nonabenzo[5]helicene (EN5H; 2), exhibits dual-state emission. Significantly, the value of |glum| of 1 is exceptionally high at 1.41×10-2 in solution and BCPL as 254 M-1 cm-1. In PMMA film, |glum| of 1 is 8.56×10-3, and in powder film, it is 5.00×10-3. This study demonstrates that nanocarbon molecules with pore defects exhibit dual-state emission properties while maintaining quite good chiral luminescence properties. It was distinguished from the aggregation-caused quenching (ACQ) effect corresponding to the nanocarbon without embedded defect. Incorporating pore defects into chiral nanocarbon molecules also simplifies the synthesis process and enhances the solubility of the resulting product. These findings suggest that the introduction of pore defects can be a viable approach to improve nanocarbon molecules.

Tröger's Base-Embedded Pillararenes─Macrocycles with Both Fixed and Conformational Chirality

Tröger's base-embedded pillararenes (P[1]TB[3]A), which combine Tröger's base (TB) with dialkoxybenzene units, were prepared via a fragment-coupling macrocyclization strategy. The TB unit in macrocycle P[1]TB[3]A provides a fixed chiral source, while 1,4-alkoxybenzene segments flip quickly to change their arrangement, which could provide reversible conformational chirality for those macrocycles. This rare example of macrocycles holding both fixed and conformational chirality lays a good foundation for expanding pillararenes using the fixed chiral source.

Dynamic Near-Infrared Circularly Polarized Luminescence Encoded by Transient Supramolecular Chiral Assemblies

Circularly polarized luminescence (CPL) is promising for applications in many fields. However, most systems involving CPL are within the visible range; near-infrared (NIR) CPL-active materials, especially those that exhibit high glum values and can be controlled spatially and temporally, are rare. Herein, dynamic NIR-CPL with a glum value of 2.5×10-2 was achieved through supramolecular coassembly and energy-transfer strategies. The chiral assemblies formed by the coassembly between adenosine triphosphate (ATP) and a pyrene derivative exhibited a red CPL signal (glum of 10-3). The further introduction of sulfo-cyanine5 resulted in a energy-transfer process, which not only led to the NIR CPL but also increased the glum value to 10-2. Temporal control of these chiral assemblies was realized by introducing alkaline phosphatase to fabricate a biomimetic enzyme-catalyzed network, allowing the dynamic NIR CPL signal to be turned on. Based on these enzyme-regulated temporally controllable dynamic CPL-active chiral assemblies, a multilevel information encryption system was further developed. This study provides a pioneering example for the construction of dynamic NIR CPL materials with the ability to perform temporal control via the supramolecular assembly strategy, which is expected to aid in the design of supramolecular complex systems that more closely resemble natural biological systems.

A Stable Chichibabin Diradicaloid with Near-Infrared Emission

Conjugated molecules with multiple radical centers such as the iconic Chichibabin diradicaloid hold promise as building blocks in materials for quantum sensing and quantum information processing. However, it is a considerable challenge to design simple analogues of the Chichibabin hydrocarbon that are chemically inert, exhibit high diradical character and emit light at a distinct wavelength that may offer an optical readout of the spin state in functional ensembles. Here we describe the serendipitous discovery of the stable TTM-TTM diradicaloid, which exhibits high diradical character, a striking sky-blue color and near-infrared (NIR) emission (in solution). This combination of properties is unique among related diradicaloids and is due to the presence of hydrogen and chlorine atoms in "just the right positions", allowing a perfectly planar, yet predominantly benzenoid bridge to connect the two sterically stabilized radical centers. In-depth studies of the optical and magnetic properties suggest that this structural motif could become a mainstay building block of organic spin materials.

Polycationic Open-Shell Cyclophanes: Synthesis of Electron-Rich Chiral Macrocycles, and Redox-Dependent Electronic States

π-Conjugated chiral nanorings with intriguing electronic structures and chiroptical properties have attracted considerable interests in synthetic chemistry and materials science. We present the design principles to access new chiral macrocycles (1 and 2) that are essentially built on the key components of main-group electron-donating carbazolyl moieties or the π-expanded aza[7]helicenes. Both macrocycles show the unique molecular conformations with a (quasi) figure-of-eight topology as a result of the conjugation patterns of 2,2',7,7'-spirobifluorenyl in 1 and triarylamine-coupled aza[7]helicene-based building blocks in 2. This electronic nature of redox-active, carbazole-rich backbones enabled these macrocycles to be readily oxidized chemically and electrochemically, leading to the sequential production of a series of positively charged polycationic open-shell cyclophanes. Their redox-dependent electronic states of the resulting multispin polyradicals have been characterized by VT-ESR, UV/Vis-NIR absorption and spectroelectrochemical measurements. The singlet (ΔES-T=-1.29 kcal mol-1) and a nearly degenerate singlet-triplet ground state (ΔES-T(calcd)=-0.15 kcal mol-1 and ΔES-T(exp)=0.01 kcal mol-1) were proved for diradical dications 12+2⋅ and 22+2⋅, respectively. Our work provides an experimental proof for the construction of electron-donating new chiral nanorings, and more importantly for highly charged polyradicals with potential applications in chirospintronics and organic conductors.

Enhanced Horizontal Dipole Orientation by Novel Penta-Helicene Anthracene-Based Host for Efficient Blue Fluorescent OLEDs

Due to the relatively low photoluminescence quantum yield (PLQY) and horizontal dipole orientation of doped films, anthracene-based fluorescent organic light-emitting diodes (F-OLEDs) have faced a great challenge to achieve high external quantum efficiency (EQE). Herein, a novel approach is introduced by incorporating penta-helicene into anthracene, presented as linear-shaped 3-(4-(10-phenylanthracen-9-yl)phenyl)dibenzo[c,g]phenanthrene (BABH) and 3-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)dibenzo[c,g]phenanthrene (NABH). These blue hosts exhibit minimal intermolecular overlap of π-π stacking, effectively suppressing excimer formation, which facilitates the effective transfer of singlet energy to the fluorescent dopant for PLQY as high as 90%. Additionally, the as-obtained two hosts of BABH and NABH have effectively demonstrated major horizontal components transition dipole moments (TDM) and high thermal stability with glass transitional temperature (Tg) surpassing 188 °C, enhancing the horizontal dipole orientation of their doped films to be 89% and 93%, respectively. The OLEDs based on BABH and NABH exhibit excellent EQE of 10.5% and 12.4% at 462 nm and device lifetime up to 90% of the initial luminance over 4500 h at 100 cd m-2, which has firmly established them as among the most efficient blue F-OLEDs based on anthracene to date to the best knowledge. This work provides an instructive strategy to design an effective host for highly efficient and stable F-OLEDs.

Longitudinal Extension of Double π-Helix Enables Near-Infrared Amplified Dissymmetry and Chiroptical Response

Near-infrared (NIR) circularly polarized light absorbing or emitting holds great promise for highly sensitive and precise bioimaging, biosensing, and photodetectors. Aiming at designing NIR chiral molecular systems with amplified dissymmetry and robust chiroptical response, herein, we present a series of double π-helical dimers with longitudinally extended π-entwined substructures via Ullmann or Yamamoto homocoupling reactions. Circular dichroism (CD) spectra revealed an approximate linear bathochromic shift with the rising number of naphthalene subunits, indicating a red to NIR chiroptical response. Particularly, the terrylene diimide-entwined dimers exhibited the strongest CD intensities, with the maximal |Δε| reaching up to 393 M-1 cm-1 at 666 nm for th-TDI[2]; and a record-high chiroptical response (|ΔΔε|) between the neutral and dianionic species of 520 M-1 cm-1 at 833 nm for th-TDI[2]Cl was achieved upon further reduction to its dianionic state. Time-dependent density functional theory (TDDFT) calculations suggested that the pronounced intensification of the CD spectra originated from a simultaneous enhancement of both electric (μ) and magnetic (m) transition dipole moments, ultimately leading to an overall increase in the rotatory strength (R). Notably, the circularly polarized luminescence (CPL) brightness (BCPL) reached 77 M-1 cm-1 for th-TDI[2]Cl, among the highest values reported for NIR-CPL emitters. Furthermore, all chiral dianions exhibited excellent air stability under ambient conditions with half-life times of up to 10 days in N-methylpyrrolidone (NMP), which is significant for future biological applications and chiroptic switches.

S-Shaped Helical Singlet Diradicaloid and Its Transformation to Circumchrysene via a Two-Stage Cyclization

Polycyclic hydrocarbons with diradical and polyradical characters usually display unique reactivities in ring-cyclization reactions. However, such reactions are rarely used to construct π-extended polycyclic aromatic hydrocarbons. Here, we describe the synthesis of an S-shaped doubly helical singlet diradicaloid compound and its facile transformation into an unprecedented circumchrysene via a two-stage ring cyclization, which includes: (1) an eletrocylization from diradicaloid precursor and (2) a Scholl reaction. The reaction mechanism was investigated through in situ spectroscopic studies, assisted by theoretical calculations. This reaction sequence yields an optically resolved π-extended [5]helicene derivative with a fluorescence quantum yield up to 85% and a circularly polarized luminescence brightness up to 6.05 M-1 cm-1 in the far-red to near-infrared regions. This sequence also yielded a highly delocalized circumchrysene molecule, exhibiting large electron delocalization, moderate fluorescence quantum yield, and multistage redox properties.

Chiral π-Conjugated Double Helical Aminyl Diradical with the Triplet Ground State

We report a neutral high-spin diradical of chiral C2-symmetric bis[5]diazahelicene with ΔEST ≈ 0.4 kcal mol-1, as determined by EPR spectroscopy/SQUID magnetometry. The diradical is the most persistent among all high-spin aminyl radicals reported to date by a factor of 20, with a half-life of up to 6 days in 2-MeTHF at room temperature. Its triplet ground state and excellent persistence may be associated with the unique spin density distribution within the dihydrophenazine moiety, which characterizes two effective 3-electron C-N bonds analogous to the N-O bond of a nitroxide radical. The enantiomerically enriched (ee ≥ 94%) (MM)- and (PP)-enantiomers of the precursors to the diradicals are obtained by either preparative chiral supercritical fluid chromatography or resolution via functionalization with the chiral auxiliary of the C2-symmetric racemic tetraamine. The barrier for the racemization of the solid tetraamine is ΔG‡ = 43 ± 0.01 kcal mol-1 in the 483-523 K range. The experimentally estimated lower limit of the barrier for the racemization of a diradical, ΔG‡ ≥ 26 kcal mol-1 in 2-MeTHF at 293 K, is comparable to the DFT-determined barrier of ΔG‡ = 31 kcal mol-1 in the gas phase at 298 K. While the enantiomerically pure tetraamine displays strong chiroptical properties, with anisotropy factor |g| = |Δε|/ε = 0.036 at 376 nm, |g| ≈ 0.005 at 548 nm of the high-spin diradical is comparable to that recently reported triplet ground-state diradical dication. Notably, the radical anion intermediate in the generation of diradical exhibits a large SOMO-HOMO inversion, SHI = 35 kcal mol-1.

A Chirally Locked Bis-perylene Diimide Macrocycle: Consequences for Chiral Self-Assembly and Circularly Polarized Luminescence

Macrocycles containing chiral organic dyes are highly valuable for the development of supramolecular circularly polarized luminescent (CPL) materials, where a preorganized chiral framework is conducive to directing π-π self-assembly and delivering a strong and persistent CPL signal. Here, perylene diimides (PDIs) are an excellent choice for the organic dye component because, alongside their tunable photophysical and self-assembly properties, functionalization of the PDI's core yields a twisted, chiral π-system, capable of CPL. However, configurationally stable PDI-based macrocycles are rare, and those that are also capable of π-π self-assembly beyond dimers are unprecedented, both of which are advantageous for robust self-assembled chiroptical materials. In this work, we report the first bay-connected bis-PDI macrocycle that is configurationally stable (ΔG⧧ > 155 kJ mol-1). We use this chirally locked macrocycle to uncover new knowledge of chiral PDI self-assembly and to perform new quantitative CPL imaging of the resulting single-crystal materials. As such, we discover that the chirality of a 1,7-disubstituted PDI provides a rational route to designing H-, J- and concomitant H- and J-type self-assembled materials, important arrangements for optimizing (chir)optical and charge/energy transport properties. Indeed, we reveal that CPL is amplified in the single crystals of our chiral macrocycle by quantifying the degree of emitted light circular polarization from such materials for the first time using CPL-Laser Scanning Confocal Microscopy.

Highly Luminescent Chiral Double π-Helical Nanoribbons

Unveiling the mechanism behind chirality propagation and dissymmetry amplification at the molecular level is of significance for the development of chiral systems with comprehensively outstanding chiroptical performances. Herein, we have presented a straightforward Cu-mediated Ullmann homocoupling approach to synthesize perylene diimide-entwined double π-helical nanoribbons encompassing dimer, trimer, and tetramer while producing homochiral or heterochiral linking of chiral centers. A significant dissymmetry amplification was achieved, with absorption dissymmetry factors (|gabs|) increasing from 0.009 to 0.017 and further to 0.019, and luminescence dissymmetry factors (|glum|) rising from 0.007 to 0.013 and eventually to 0.015 for homochiral double π-helical oligomers. The disparity of magnetic transition dipole moment (m) densities in homochiral and heterochiral tetramers by time-dependent density functional theory calculations confirmed that homochiral oligomerization can maximize the total m, which is favorable for achieving ever-increasing g factors. Notably, these double π-helices exhibited exceptional photoluminescence quantum yields (ΦPL) ranging from 83 to 95%. The circularly polarized luminescence brightness (BCPL) eventually reached a remarkable 575 M-1 cm-1 for the homochiral tetramer, which is among the highest values reported for chiral small molecules. This kind of linearly extended double π-helices offers a platform for a comprehensive understanding of the mechanism behind chirality propagation and dissymmetry amplification.

Rapid Synthesis of Chiral Figure-Eight Macrocycles Using a Preorganized Natural Product-Based Scaffold

Chiral D2 -symmetric figure-eight shaped macrocycles are promising scaffolds for amplifying the chiroptical properties of π-conjugated systems. By harnessing the inherent and adaptable conformational dynamics of a chiral C2 -symmetric bispyrrolidinoindoline (BPI) manifold, we developed an enantio-divergent modular synthetic platform to rapidly generate a diverse range of chiral macrocycles, spanning from 14- to 66-membered rings, eliminating the need for optical resolution. Notably, a 32-membered figure-eight macrocycle showed excellent circularly polarized luminescence (CPL: |glum |=1.1×10-2 ) complemented by a robust emission quantum yield (Φfl =0.74), to achieve outstanding CPL brightness (BCPL : ϵ×Φfl ×|glum |/2=480). Using quadruple Sonogashira couplings, this versatile synthetic platform enables precise adjustments of the angle, distance, and length among intersecting π-conjugated chromophores. Our synthetic strategy offers a streamlined and systematic approach to significantly enhance BCPL values for a variety of chiral D2 -symmetric figure-eight macrocycles.

Phenothiazine cyclic hexamers: synthesis, properties, and complexation behavior with C60

Phenothiazine cyclic hexamers linked at the 3,7-positions were synthesized. Effects of the cyclic structure as well as substituent effects of the nitrogen atom were disclosed. Furthermore, the cyclic hexamer encapsulated C60 inside the ring in a 1 : 1 ratio giving a Saturn-type complex in solution. The structure and interactions were discussed based on DFT calculations.

B-N Covalent Bond Embedded Double Hetero-[n]helicenes for Pure Red Narrowband Circularly Polarized Electroluminescence with High Efficiency and Stability

Chiral B/N embedded multi-resonance (MR) emitters open a new paradigm of circularly polarized (CP) organic light-emitting diodes (OLEDs) owing to their unique narrowband spectra. However, pure-red CP-MR emitters and devices remain exclusive in literature. Herein, by introducing a B-N covalent bond to lower the electron-withdrawing ability of the para-positioned B-π-B motif, the first pair of pure-red double hetero-[n]helicenes (n = 6 and 7) CP-MR emitter peaking 617 nm with a small full-width at half-maximum of 38 nm and a high photoluminescence quantum yield of ≈100% in toluene is developed. The intense mirror-image CP light produced by the enantiomers is characterized by high photoluminescence dissymmetry factors (gPL ) of +1.40/-1.41 × 10-3 from their stable helicenes configuration. The corresponding devices using these enantiomers afford impressive CP electroluminescence dissymmetry factors (gEL ) of +1.91/-1.77 × 10-3 , maximum external quantum efficiencies of 36.6%/34.4% and Commission Internationale de I'Éclairage coordinates of (0.67, 0.33), exactly satisfying the red-color requirement specified by National Television Standards Committee (NTSC) standard. Notably a remarkable long LT95 (operational time to 95% of the initial luminance) of ≈400 h at an initial brightness of 10,000 cd m-2 is also observed for the same device, representing the most stable CP-OLED up to date.

Synthesis of π-Conjugated Chiral Aza/Boracyclophanes with a meta and para Substitution

We herein describe the synthesis of a new class of axially chiral aza/boracyclophanes (BDN1, BXN1, BDB1 and BXB1) using binaphthyls as chiral building blocks and the main-group (B/N) chemistry with tunable electronic effects. All macrocycles substituted with triarylamine donors or triarylborane acceptors are strongly luminescent. These macrocycles showed two distinct meta and para π-conjugation pathways, leading to the formation of quasi figure-of-eight and square-shaped conformations. Interestingly, comparison of such structural models revealed that the former type of macrocycles BXN1 and BXB1 gave higher racemization barriers relative to the other ones. The results reported here may provide a new approach to engineer the optical stability of π-conjugated chiral macrocycles by controlling π-substitution patterns. The ring constraints induced by macrocyclization were also demonstrated to contribute to the configurational persistence as compared with the open-chain analogues p-BTT and m-BTT.

Advances in circularly polarized luminescence materials based on chiral macrocycles

Development of circularly polarized luminescence (CPL) materials utilizing supramolecular strategies has recently attracted increasing interest in supramolecular chemistry and materials science. Chiral macrocycles, especially chiral macrocyclic hosts, have stable structures, adjustable internal cavities to encapsulate different guests, and host-guest complexation to induce special photophysical properties. Consequently, various CPL materials based on chiral macrocycles have been developed during the last decade. To gain a better understanding of this rapidly developing research area, it is necessary and also important to summarize the advances in CPL materials based on chiral macrocycles. In this review, CPL materials from different chiral macrocycles, especially classical and newly reported chiral macrocyclic hosts and their derivatives, will be comprehensively summarized. It is believed that this review will be of guiding significance and also very helpful for the development of macrocyclic chemistry and CPL materials.

Chiral Luminescent Aza[7]helicenes Functionalized with a Triarylborane Acceptor and Near-Infrared-Emissive Doublet-State Radicals

This paper presents new chiral luminescent molecules (N7-BMes2 and N7-TTM) using configurationally stable aza[7]helicene (1) as a universal heteroatom-doped chiral scaffold. The respective reactions of electron-donating 1 with a triarylborane acceptor via palladium-catalyzed Buchwald-Hartwig C-N coupling and with the open-shell doublet-state TTM radical via nucleophilic aromatic substitution (SN2Ar) resulted not only in tunable emissions from blue to the NIR domain but also in significantly enhanced emission quantum efficiency up to Φ = 50%.