Dissymmetric Factor Research Articles

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.

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

Abstractπ‐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.

On‐Demand Fabrication and Manipulation of Single Plasmonic Trimers for Ultrasensitive Enantiomer Detection

AbstractThe capability of plasmonic nanostructures in generating superchiral near‐fields holds great potential for a wide range of applications, including enantioselective sensing, medical diagnosis, and chirality‐based bioimaging. To implement high‐performance chiral nanophotonic devices, achieving in situ tuning of chiroptical activity in plasmonic nanostructures is highly desirable yet remains a formidable challenge. Here, a straightforward method is developed for deterministic assembly of plasmonic nanosphere trimers using spectroscopy‐assisted nano‐manipulation. The technique offers in situ, real‐time, and site‐specific control over the chiroptical response of trimers by adjusting their vertex angle and in‐plane orientation. The combination of numerical simulations with the Born‐Kuhn model reveals that oblique excitation effectively induces the symmetry breaking of the trimer structure, resulting in a preferential response of two distinct hybridized plasmonic modes to the handedness of light. Consequently, this yields a significant chiroptical response with the g factor up to 0.37. Remarkably, the trimer with an optimized obtuse angle exhibits a 193‐fold enhancement of optical chirality density, enabling the detection of molecular chirality with a record‐large spectral dissymmetric factor of 12 nm. The study facilitates the rational design of plasmonic nanostructures, offering promising prospects for chiral sensing at the single‐molecule level and asymmetric photocatalysis.

Tetraphenylethylene-based conjugated polymers with valine-containing side chains: Aggregation-induced emission, helical self-assembly, complexation-induced circularly polarized luminescence

Realizing high circularly polarized luminescence (CPL) in polymer system is an important but challenging task. Herein, we provide a strategy for designing conjugated polymers with high CPL performance upon the complexation with mandelic acids. Two tetraphenylethylene (TPE)-based conjugated polymers, l-P1 and d-P1, were synthesized by Sonogashira polycoupling reactions between the TPE-containing diethynyl monomer and dibromo aryl monomers carrying valine methyl ester groups. Both the polymers showed aggregation-induced emission (AIE) properties and the capabilities to self-assemble into regular helical nanostructures on nanoscale and fluorescent microfibers on microscale. They exhibited weak circular dichroism (CD) signals; upon the complexation with R/S-mandelic acids, their CD absorption and fluorescence emission can be efficiently enhanced. The composite films of l/d-P1 and R/S-mandelic acids exhibited excellent complexation-induced CPL properties with the absolute luminescence dissymmetric factor (glum) up to 0.01 and the fluorescence quantum yield up to 26.8%; the glum values showed little dependence on their emission wavelength. Various types of carboxyl acids have been screened and only mandelic acids show significantly chiroptical induction. The specific interaction between mandelic acids and l/d-P1 also makes the latter promising candidates for the enantioselective recognition of chiral organic molecules.

Chiral Polymer‐Organic Molecule Composite with Circularly Polarized Thermally Activated Delayed Fluorescence and Room‐Temperature Phosphorescence by Bridging Effect of Hydrogen Bond

AbstractCircularly polarized luminescence is essential to chiral and photonic science, but achieving circularly polarized thermally activated delayed fluorescence (CP‐TADF) and circularly polarized room‐temperature phosphorescence (CP‐RTP) simultaneously remains a great challenge. This is because it is difficult to satisfy simultaneously the stable triplet exciton, appropriate energy gap, and the regular chiral environment. Herein, a simple strategy is reported to construct a persistent photoluminescent system, which can achieve TADF and RTP simultaneously by suppressing the non‐radiative transition decay of the triplet exciton through intermolecular hydrogen bonding between acridine flavin (AF) and rigid polymer network. The persistent photoluminescent composite exhibited ultra‐long lifetimes and high quantum yields. Then, a rarely multi‐circularly polarized photoluminescence system containing CP‐TADF and CP‐RTP is constructed by the co‐assembly of cellulose nanocrystals, polyvinyl alcohol, and AF. By utilizing the cholesteric structure, photonic band gap of chiral photonic crystals, and the stabilization mechanism of triplet exciton by intermolecular hydrogen bonding between the light emitter and rigid polymer, chiral photoluminescent films exhibited rare optical properties simultaneously: multi‐circularly polarized photoluminescence emission, high and tunable dissymmetric factor, significant quantum yield, and ultralong lifetimes, which are not reported before and broaden the perspective for multi‐circularly polarized luminescence.

Fluorescence-Selective Absorption and Circularly Polarized Fluorescence Energy Transfer Assist the Generation of Multicolor Circularly Polarized Luminescence in Chiral Helical Polyacetylene-Based Janus Nanofibers.

Chiroptical nanomaterials with circularly polarized luminescence (CPL) performance have aroused increasing attention. Herein, multicolor CPL-active Janus nanofibers are prepared through a simple parallel electrospinning method using chiral helical polyacetylenes as the chiral source and achiral fluorophores as the fluorescent source. Interestingly, despite a direct spatial isolation between the chiral component and the fluorescent component, blue and green CPL emissions can still be obtained due to the fluorescence-selective absorption behavior of chiral helical polyacetylenes, with a satisfactory dissymmetric factor (glum) of 2 × 10-2 and 2.5 × 10-3, respectively. Moreover, by taking advantage of the circular polarization fluorescence energy transfer process, red CPL emission is further achieved using the obtained blue and green CPL as energy donors and the achiral red fluorophore as an energy acceptor. The present work offers a facile approach to prepare multilevel-structured chiroptical materials with promising application potentials in a flexible photoelectric device.

Construction of Circular Polarized Luminescence Molecules for Intense Near Infrared OLEDs

AbstractThe exploration of organic near‐infrared (NIR) luminescence, along with circularly polarized luminescence (CPL), is of vital importance due to its significance in medical and optoelectronic applications. Integrating a chiral unit into a D–A molecular structure in this research realized emission peaks at 744 nm, exhibiting a dissymmetric factor of −1.67 × 10−3. The introduced chiral TPA derivative not only imparts aggregation‐induced emission properties and CPL capabilities but also induces a redshift in the emission spectrum. Consequently, the fabricated NIR organic light‐emitting devices (OLEDs), achieve maximum electroluminescent peaks at 748 nm in nondoped devices with the external quantum efficiency of 13.7% in doped devices. This pioneering research provides inspiration for the design of NIR molecules possessing CPL properties in the future, particularly in promoting the application of intense NIR‐OLEDs.

Color-Tunable Perovskite Nanomaterials with Intense Circularly Polarized Luminescence and Tailorable Compositions.

The ability to design halide perovskite nanocrystals (PNCs) with circularly polarized luminescence (CPL) offers exceptional potential in photonic technologies. Despite recent inspiring advances, the creation of PNCs with full-color tailorablity, outstanding CPL, and long-term stability remains a substantial challenge. Herein, a robust strategy to craft CPL-active PNCs is reported, exhibiting appealing full-color tunable wavelengths, enhanced CPL, and prolonged stability. In contrast to conventional methodologies, this strategy utilizes chiral nematic mesoporous silica (CNMS) as host to render in situ confined growth of diverse achiral PNCs. By strategically engineering photonic bandgap, adjusting loading amount of PNCs, and manipulating cations/anion compositions of PNCs, robust CPL responses with tunable wavelength and intensity are successfully obtained. The resulting PNCs-CNMS achieves stable CPL emissions with full-color tunability and impressive luminescent dissymmetric factors up to -0.17. Remarkably, silica-based hosts as a protective barrier confer exceptional resistance to humidity, photodegradation, and thermal stability, even up to 95 °C. Furthermore, the ability to achieve reversible CPL switching within PNCs-CNMS is attainable by leveraging the responsiveness of CNMS matrix or dynamic behavior of impregnated PNCs. Additionally, circularly polarized light-emitting diode devices based on PNCs-CNMS can be conveniently fabricated. This research affords a powerful platform for designing functional chiroptical materials.

Tether-entangled conjugated helices.

A new design concept, tether-entangled conjugated helices (TECHs), is introduced for helical polyaromatic molecules. TECHs consist of a linear polyaromatic ladder backbone and periodically entangling tethers with the same planar chirality. By limiting the length of tether, all tethers synchronously bend and twist the backbone with the same manner, and change it into a helical ribbon with a determinate helical chirality. The 3D helical features are customizable via modular synthesis by using two types of synthons, the planar chiral tethering unit (C 2 symmetry) and the docking unit (C 2h symmetry), and no post chiral resolution is needed. Moreover, TECHs possess persistent chiral properties due to the covalent locking of helical configuration by tethers. Concave-type and convex-type oligomeric TECHs are prepared as a proof-of-concept. Unconventional double-helix π-dimers are observed in the single crystals of concave-type TECHs. Theoretical studies indicate the smaller binding energies in double-helix π-dimers than conventional planar π-dimers. A concentration-depend emission is found for concave-type TECHs, probably due to the formation of double-helix π-dimers in the excited state. All TECHs show strong circularly polarized luminescence (CPL) with dissymmetric factors (|g lum|) generally over 10-3. Among them, the (P)-T4-tBu shows the highest |g lum| of 1.0 × 10-2 and a high CPL brightness of 316 M-1 cm-1.

The influence of heteroatoms on the circularly polarized luminescence performance of [7]helicene derivatives: aromatic vs. non-aromatic five-membered rings.

Helicenes are promising candidates for circularly polarized luminescence (CPL) materials, although the performance is poor due to the unsatisfactory dissymmetric factor (glum) and fluorescence quantum efficiency (ΦF). Herein, the influence of heteroatoms (C, Si, Ge, O, S and Se) on the electronic structures and chiroptical properties of [7]helicene derivatives is systematically investigated using density functional theory (DFT) and time-dependent DFT calculations combined with the thermal vibration correlation function theory. The results reveal that the non-radiative energy consumption processes for helicene systems are closely related to the variation of bond length upon electronic excitation. Moreover, by introducing five-membered rings and heteroatoms, the dipole-forbidden S1 → S0 emission of [7]helicene changes to dipole-allowed transition due to the rearrangement of occupied orbitals and lifting of the nearly degenerate orbitals, resulting in an enhancement of ΦF. As the heteroatomic radius increases, ΦF decreases while the glum increases. Compared with the derivatives containing aromatic five-membered rings ([7]H-O, [7]H-S, and [7]H-Se), the non-aromatic counterparts ([7]H-C, [7]H-Si, and [7]H-Ge) exhibit a balance in ΦF and glum values. The present study helps to clarify the relationship between structures and chiroptical properties and offers a feasible strategy for the future design of helicene-based CPL materials.

Tunable circular polarization room temperature phosphorescence with ultrahigh dissymmetric factor by cholesteric liquid crystal elastomers

Tunable circular polarization room temperature phosphorescence with ultrahigh dissymmetric factor by cholesteric liquid crystal elastomers

A Fused [5]Helicene Dimer with a Figure-Eight Topology: Synthesis, Chiral Resolution, and Electronic Properties.

Chiral shape-persistent molecular nanocarbons are promising chiroptical materials; their synthesis, however, remains a big challenge. Herein, we report the facile synthesis and chiral resolution of a double-stranded figure-eight carbon nanobelt 1 in which two [5]helicene units are fused together. Two synthetic routes were developed, and, in particular, a strategy involving Suzuki coupling-mediated macrocyclization followed by Bi(OTf)3 -catalyzed cyclization of vinyl ether turned out to be the most efficient. The structure of 1 was confirmed by X-ray crystallographic analysis. The isolated (P,P)- and (M,M)- enantiomers show persistent chiroptical properties with relatively large dissymmetric factors (|gabs |=5.4×10-3 and |glum |=1.0×10-2 ), which can be explained by the effective electron delocalization along the fully conjugated belt and the unique D2 symmetry. 1 exhibits local aromatic character with a dominant structure containing eight Clar's aromatic sextet rings.

A Fused [5]Helicene Dimer with a Figure‐Eight Topology: Synthesis, Chiral Resolution, and Electronic Properties

AbstractChiral shape‐persistent molecular nanocarbons are promising chiroptical materials; their synthesis, however, remains a big challenge. Herein, we report the facile synthesis and chiral resolution of a double‐stranded figure‐eight carbon nanobelt 1 in which two [5]helicene units are fused together. Two synthetic routes were developed, and, in particular, a strategy involving Suzuki coupling‐mediated macrocyclization followed by Bi(OTf)3‐catalyzed cyclization of vinyl ether turned out to be the most efficient. The structure of 1 was confirmed by X‐ray crystallographic analysis. The isolated (P,P)‐ and (M,M)‐ enantiomers show persistent chiroptical properties with relatively large dissymmetric factors (|gabs|=5.4×10−3 and |glum|=1.0×10−2), which can be explained by the effective electron delocalization along the fully conjugated belt and the unique D2 symmetry. 1 exhibits local aromatic character with a dominant structure containing eight Clar's aromatic sextet rings.

"First Come, First Served" and Threshold Effects in a Central-to-Planar-to-Helical Hierarchical Chiral Induction.

Perylene diimide tethered pillar[5]arene derivatives form aggregates in non-polar organic solvents, and the complexation of cationic amino acid ethyl ester (cAA-OEt) with the aggregates induce a central-to-planar-to-helical chirality transfer, leading to intensive circular dichroism (CD) signals having dissymmetric factors (gabs ) of up to 3.67×10-2 . The hierarchical chiral induction exhibited an intriguing threshold dose effect, namely, the chiral induction does not occur in the low concentration range of cAA-OEt but is triggered when cAA-OEt exceeds a threshold concentration. The inhibited interconversion between the Rp and Sp conformers of pillar[5]arene, which is further restricted in the aggregation, plays a crucial role in the threshold effect. When adding enantiopure cAA-OEt first to the threshold concentration and then adding an equal amount of the antipodal cAA-OEt to give cAA-OEt in racemic form, CD spectra having the same sign as the CD induced by first adding pure cAA-OEt were induced, thus showing an unprecedented "first come, first served" effect.

“First Come, First Served” and Threshold Effects in a Central‐to‐Planar‐to‐Helical Hierarchical Chiral Induction

AbstractPerylene diimide tethered pillar[5]arene derivatives form aggregates in non‐polar organic solvents, and the complexation of cationic amino acid ethyl ester (cAA‐OEt) with the aggregates induce a central‐to‐planar‐to‐helical chirality transfer, leading to intensive circular dichroism (CD) signals having dissymmetric factors (gabs) of up to 3.67×10−2. The hierarchical chiral induction exhibited an intriguing threshold dose effect, namely, the chiral induction does not occur in the low concentration range of cAA‐OEt but is triggered when cAA‐OEt exceeds a threshold concentration. The inhibited interconversion between the Rp and Sp conformers of pillar[5]arene, which is further restricted in the aggregation, plays a crucial role in the threshold effect. When adding enantiopure cAA‐OEt first to the threshold concentration and then adding an equal amount of the antipodal cAA‐OEt to give cAA‐OEt in racemic form, CD spectra having the same sign as the CD induced by first adding pure cAA‐OEt were induced, thus showing an unprecedented “first come, first served” effect.

DNA-induced circularly polarized luminescence of helicene racemates.

Enantiopure helicenes have been extensively investigated due to their outstanding chiroptical properties, while helicene racemates are considered as chiroptically silent. Here, we describe a facile method to produce circularly polarized luminescence (CPL) from helicene racemates via supramolecular association with DNA in aqueous solution. Racemic cationic helicene derivatives are immobilized in the grooves of commercially available double-stranded right-handed DNA, and the discrimination of left- and right-handed helicenes by chiral DNA is monitored by single molecule force spectroscopy. This subsequently leads to the generation of prominent CPL with dissymmetric factor |glum | of close to 0.01, which is approximate to enantiopure helicenes. The strategy developed in this work avoids the tedious and expensive chiral resolution process and provides a distinctive insight into the fabrication of CPL-emitting systems.

Intense Circularly Polarized Fluorescence and Room-Temperature Phosphorescence in Carbon Dots/Chiral Helical Polymer Composite Films

Chiral carbon dots (C-dots) with a circularly polarized fluorescence (CPF) property have attracted tremendous attention due to their significant applications in chiral optoelectronics and theranostics. However, constructing circularly polarized room-temperature phosphorescent (CPRTP) C-dots remains a great challenge. Herein, a strategy is established to achieve efficient CPF and CPRTP emissions in C-dots/chiral helical polymer bilayer composite film. Taking advantage of the chiral filter effect of chiral helical polymer, intense CPF and CPRTP emissions with large dissymmetric factors up to 1.4 × 10-1 and 1.2 × 10-2 are respectively obtained, even though there is only a simple interface contact between the C-dots layer and the chiral helical polymer layer. More importantly, white-color CPF emission and multiple information display and encryption are further realized based on the prepared chiral luminescent composite films.

Assembly–disassembly switching of chiral sheet assembly for controlled circularly polarized luminescence

AbstractAlthough substantial advances have been made regarding synthetic chiral assemblies, obtaining the two‐dimensional (2D) system with a sophisticated supramolecular chirality remains challenging. Herein, we report the switchable supramolecular chiral 2D materials via donor‐acceptor interaction between a pyrene amphiphile and 7,7,8,8‐tetracyanoquinodimethane (TCNQ). The resulting supramolecular chiral sheets spontaneously disassemble when TCNQ is irreversibly photo‐reduced to its anion. Subsequent additions of TCNQ drive the disassembled molecules to repeatedly form optically active sheet structures, demonstrating that the assembled materials exist transiently only while TCNQ is supplied. The chiral sheets emit intense circularly polarized light with a large luminescence dissymmetric factor (glum).

Alternating chiral and achiral spacers for constructing two-dimensional chiral hybrid perovskites toward circular-polarization-sensitive photodetection.

The intrinsic integration of structural flexibility, chiroptical activity, and photoelectric properties endows the two-dimensional (2D) chiral hybrid perovskites (CHPs) with significant application potential in chiroptoelectronics and spintronics. However, the scarcity of suitable chiral organic ligands severely hinders their extensive construction, necessitating the development of new strategies for designing 2D CHPs. Herein, by exploiting a half substitution method, we created a pair of 2D CHPs with alternating cations in the interlayer space (ACI), (R/S-PPA)(PA)PbBr4 (2R/2S, PPA = 1-phenylpropylamine, PA = n-pentylamine), from the achiral Ruddlesden-Popper (RP) (PA)2PbBr4 (1). The successful chirality transfer induces 2R/2S to crystallize in the chiral P212121 space group and thus acquire appealing chiroptical activity. Consequently, the single-crystal devices of 2R exhibit good distinguishability to the left- and right-handed circularly polarized 405 nm lights with a photocurrent dissymmetric factor of 0.10 at 10 V bias. This work demonstrates an intriguing achiral RP to chiral ACI motif reconstruction in 2D halide hybrid perovskites, opening a door for expanding the family of 2D CHPs.

Photoprogrammable circularly polarized phosphorescence switching of chiral helical polyacetylene thin films

The developments of pure organic room-temperature phosphorescence (RTP) materials with circularly polarized luminescence (CPL) have significantly facilitated the future integration and systemization of luminescent material in fundamental science and technological applications. Here, a type of photoinduced circularly polarized RTP materials are constructed by homogeneously dispersing phosphorescent chiral helical substituted polyacetylenes into a processable poly(methyl methacrylate) (PMMA) matrix. These substituted polyacetylenes play vital roles in the propagation of CPL and present prominently optical characteristics with high absorption and luminescent dissymmetric factors up to 0.029 (gabs) and 0.019 (glum). The oxygen consumption properties of the films under UV light irradiation endow materials with dynamic chiro-optical functionality, which can leverage of light to precisely control and manipulate the circularly polarized RTP properties with the remarkable advantages of being contactless, wireless and fatigue-resistant. Significantly, the distinct materials with dynamic properties can be used as anti-counterfeiting materials involving photoprogrammability.