Cascading chirality from molecule to twisted microstructures with amplified circularly polarized luminescence.

Chirality transfer, induction, and circularly polarized luminescence (CPL) using supramolecular hosts, such as macrocycles and cages, have been explored for wide-ranging applications in chiral reco...

Utilizing achiral fluorophores to fabricate circularly polarized luminescence (CPL) materials is of significant importance in both fundamental research and practical applications; chirality transfer has become an indispensable process in routine efforts reported so far. However, this may restrict or even become a bottleneck in further advancing CPL materials starting from achiral fluorophores. Inspired by biological light-harvesting architectural systems, we attempt to establish a new strategy, i.e., circularly polarized fluorescence energy transfer (CPF-ET) to explore multicolor CPL films in the absence of chirality transfer. CPL has been successfully realized through both radiative energy transfer and nonradiative energy transfer. The material systems consist of chiral fluorescent helical polyacetylene working as a circularly fluorescence polarized energy donor and achiral fluorophores as an energy acceptor. Achiral acceptors absorb circularly polarized fluorescence energy from the donor and hence emit the corresponding CPL; accordingly, chirality transfer is no longer an indispensable condition, and the sense of the CPL emission of the achiral fluorophores is controlled by the chiral fluorescent polymer. Moreover, multicolor CPL films can be simply prepared by employing varying achiral fluorophores. This work provides a facile and versatile platform for achieving CPL by taking advantage of achiral fluorophores.

Co-assembling nanostructures with achiral luminescent moieties represents a significant approach for developing circularly polarized luminescence (CPL) materials. However, for chiral nanotube structures, it remains unclear whether their inner and outer surfaces exhibit equivalent induction effects. Here, enantiomeric C3-symmetric chiral methylphenylalanine derivatives were designed, and uniform supramolecular helical nanotubes were successfully fabricated. These helical nanotubes serve as host materials for the selective loading of achiral luminescent organic dye or inorganic quantum dots (QDs) into their inner channels or onto their outer surfaces via co-assembly. It was revealed that through chiral transfer, the achiral luminescent units acquired CPL activity upon integration with the chiral nanotubes, achieving dissymmetry factors (glum) on the order of 10-2 to 10-3, respectively. Interestingly, the CPL signals induced by the inner and outer surfaces exhibited opposite signs, with the signal from the inner surface being ten times stronger than that from the outer surface. Further structural analysis indicated that the concave geometry and nanoconfinement effects of the inner surface contributed to the CPL sign inversion and the enhanced luminescence dissymmetry. This work provides a novel and versatile platform for customizing the fluorescence and CPL properties of achiral luminescent units.

Tunable AI-CPL behavior by regulation of microstructure of AIE-active isomers through chiral emissive liquid crystals

The chirality of a supramolecular assembly provides particularly valuable information because the bonding nature of noncovalent interactions, such as electrostatic interactions, π effects, van der Waals forces, and hydrophobic effects, makes the development of supramolecular assemblies an attractive and useful approach in chiral induction, chiral amplification, and chirality transfer. However, chiroptical measurements of optically anisotropic samples cannot be generally achieved with modern chiroptical spectrophotometric methods such as circular dichroism (CD) or circular birefringence (CB) and circularly polarized luminescence (CPL) that are based on polarization modulation techniques because of the coupling effect of the nonideal optics and the electronics with strong macroscopic anisotropies, that is, nonchiral signals related to linearly polarized phenomena. These artifact signals are often much stronger than the chiroptical signals. Only CD and CPL spectrophotometers developed in 2001 and 2016, respectively, and integrated into a Stokes–Mueller matrix analysis for optically anisotropic samples are capable of obtaining accurate chirality measurements of samples with macroscopic anisotropies. Therefore, these spectrophotometers enable chiral investigations of optically anisotropic samples, for example, single crystals, supramolecular assemblies, gels, films, membranes, polymers, and liquid crystals. This focus review presents a short and elementary discussion of the chiroptical measurement techniques for optically anisotropic samples in supramolecular science and signal interpretation in polarization spectroscopy.

Solid-state host-guest complexation shows great potential in the fabrication of chiroptical and phosphorescent materials. Developing chiral hosts toward achiral guests with a wide guest scope would expand the chiroptical application, which however remains a major challenge. Here, we report the steroid-aromatic compound complexation in the solid state that could realize effective chirality transfer, circularly polarized luminescence, and room temperature phosphorescence (RTP). Progesterone shows cocrystallization behavior toward a wide scope of guests through CH-π interaction, which also offers a rigid yet chiral microenvironment to entrap aromatic luminophores within the cavities or channels. Depending on the geometry of the guests, the handedness of the Cotton effects and circularly polarized luminescence could be tuned. Host-guest complexation not only gave rise to Cotton effects and circularly polarized luminescence but also stabilized the triplet state of bromo-compounds to achieve RTP and circularly polarized phosphorescence. This work first illustrates the application of steroid complexation in the chiroptical and phosphorescent materials, which shows potential in the display and information aspects.

Host-guest chemistry of chiral metal-organic frameworks (MOFs) has endowed them with circularly polarized luminescence (CPL), it is still limited for MOFs to systematically tune full-color CPL emissions and sizes. This work directionally assembles the chiral ligands, metal sites and organic dyes to prepare a series of crystalline enantiomeric D/L-Cd/Zn-n MOFs (n=1~5, representing the adding amount of dyes), where D/L-Cd/Zn with the formula of Cd2(D/L-Cam)2(TPyPE) and Zn2(D/L-Cam)2(TPyPE) (D/L-Cam=D/L-camphoric acid, TPyPE=4,4',4'',4'''-(1,2-henediidenetetra-4,1-phenylene)tetrakis[pyridine]) were used as the chiral platforms. The framework-dye-enabled emission and through-space chirality transfer facilitate D/L-Cd/Zn-n bright full-color CPL activity. The ideal yellow CPL of D-Cd-5 and D-Zn-4, with |glum| as 4.9 × 10-3 and 1.3×10-3 and relatively high photoluminescence quantum yield of 40.79 % and 45.40 %, are further assembled into a white CPL light-emitting diode. The crystal sizes of D/L-Cd/Zn-n were found to be strongly correlated to the types and additional amounts of organic dyes, that the positive organic dyes allow for the preparation of > 7 mm bulks and negative dyes account for sub-20 μm particles. This work opens a new avenue to fabricate full-color emissive CPL composites and provides a potentially universal method for controlling the size of optical platforms.

Spherical chiral polyrotaxanes (CPRs) with steerable circularly polarized luminescence (CPL) are intriguing as advanced chiroptical materials but have not been reported to date. Here, we constructed spherical chiral polyrotaxane (CPR) materials with steerable CPL by utilizing cyclodextrins (α-, β-, or γ-CyD) as the chiral wheel. Importantly, the structure and the CPL performance of the CPR materials can be regulated by varying the feeding amount and the type of cyclodextrin (α-, β-, or γ-CyD). It was found that the spherical reticular frame and the chiral polyrotaxane structure were indispensable for CPL generation of spherical CPRs due to the strengthening of confined chirality transfer, as shown by structural and spectral characterization. Remarkably, spherical β-CyD/CPR at feed(C/B) = 4, 8, and 16 showed a higher quantum yield and a longer photoluminescence lifetime in comparison with those of α-CyD/CPR and γ-CyD/CPR. This work demonstrates an example of a CPL-active spherical CPR and provides insight into macrocyclic size-dependent CPL generation through a mechanically interlocked strategy and covalent reticular chemistry, which will be helpful for the future design of high-performance CPL materials.

Circularly polarized luminescence (CPL) has emerged as a critical technology for anticounterfeiting and optical display applications due to its unique chiroptical properties. We report a multicolor CPL-emitting elastomeric film (P37/PSK@SiO2-PDMS) that synergistically combines chiral helical polyacetylene (P37) and a surface-engineered perovskite (PSK@SiO2) through hydrogen-bond-directed assembly. Confinement within the PDMS matrix drives P37 to self-assemble into a chiral supramolecular structure through hydrogen bonding, inducing a chiroptical inversion. Simultaneously, surface modification of PSK@SiO2 enhances its compatibility with PDMS while enabling efficient chirality and energy transfer from P37 via interfacial hydrogen bonds. The resulting material exhibits exceptional CPL performance, achieving a maximum dissymmetry factor of 4.3 × 10-2 and a high photoluminescence quantum yield up to 67%. The PDMS matrix not only stabilizes the PSK components but also enables reversible, strain-tunable CPL modulation through its elastomeric properties. This work establishes a hydrogen-bonding paradigm for designing high-performance chiral PSK materials, while demonstrating their potential for dynamic photonic applications.

Detecting chiral/helical interactions among noncharged molecules and polymers is difficult due to their unlimited intra- and intermolecular rotational freedom. To clarify the chirality and/or helicity transfer from a chiral polymer to noncharged achiral molecules, we chose stiff cellulose triacetate (CTA) and cellulose acetate butyrate (CABu) as nonchromophoric helical/chiral polymers. Here, we highlighted stiff 9,9-dialkylfluorene oligomers and polymers (repeating number n = 1, 2, 3, 5, 7, 47, 201) as achiral chromophoric luminophores. These fluorenes revealed clear circularly polarized luminescence (CPL) and bisignate circular dichroism (CD) signals when embedded into CTA and CABu films. In the ground state, when n = 1–7, CTA and CABu commonly induced (+)-CD signals, whereas when n ≥ 47, they induced (+)- and (−)-CD signs, respectively. In the photoexcited state, when n ≥ 3, CTA and CABu induced (+)- and (−)-CPL signs, respectively. Upon comparing the ground and photoexcited states, when n = 2–7, CABu induced (+)-CD and (−)-CPL signs, whereas when n ≥ 3, CTA induced the same (+)-CD and (+)-CPL signs. A conflict between the d-glucose chirality and main-chain helicity was assumed to be responsible for these anomalies because CTA and CABu, despite being common frameworks of β(1→4)-linked d-glucose residues, prefer left- and right-handed helicities, respectively. Molecular mechanics/molecular dynamics simulations suggested intermolecular C–H/O═C interactions between H–C (due to the methylene group of the dioctylfluorenes) and O═C (due to the acetyl group attached to the d-glucose of CTA). This simulation was confirmed by the first detection of a clear cross-peak at 13C═O (δC = 170.6 ppm, CTA) and the finding CH2 protons (δH = 2.55 ppm, fluorene with n = 201) represented the shortest C–1H/O═13C distance according to the phase-modulated Lee–Goldburg homonuclear decoupling of solid-state 1H–13C HETCOR NMR spectroscopy. Moreover, the first photoinduced change in the real-time CPL/PL amplitude measurement of optically active fluorenes in CTA revealed that the stability of the chiroptical state increases as n increases and remains unchanged when n ≥ 47.

The regulation of interchromophoric interactions in multichromophoric systems is crucial for developing high-performance photofunctional materials. In this study, we present a novel self-assembly strategy to construct isomeric decker complexes, denoted as S1 and S2, which integrate disparate chromophores, achiral BODIPY and chiral binaphthyl moieties. This isomerization results in distinct chromophore packing modes. In the case of S1, the BODIPY and binaphthyl moieties are arranged in a relatively loose manner (∼6.0 Å), enabling efficient FRET and preserving the strong locally excited (LE) emission (Φ F = 91.3%) characteristic of the BODIPY unit. In contrast, for S2, the denser packing between the BODIPY and binaphthyl moieties (∼4.8 Å) leads to through-space charge transfer (TSCT) and weak charge transfer (CT) emissions (Φ F = 8.6%). Notably, only complex (R)/(S)-S1 shows mirror-image circular dichroism (CD) signals based on chirality transfer and circularly polarized luminescence (CPL), as supported by TD-DFT calculations, which reveal that the binaphthyl moiety alters the angle between the electric transition dipole moment (μ) and the magnetic transition dipole moment (m).

By utilizing a confined space inside a coordination capsule consisting of achiral components, we achieve trimeric structures composed of acetic acid and 2,3-disubstituted tartaric acid derivatives. Steric and electronic interactions between the substituents on the tartaric acid and 2,2'-bipyridyl arms of the capsule permit the transfer of the chirality of the tartaric acid to the capsule, resulting in diastereoenrichment of the host-guest complexes of up to 92 % de. The chiral templates can be washed away with diethyl ether, leaving an enantiomerically enriched capsule. The resulting capsule biases the dynamic axial chirality of a 4,4'-diacetoxybiphenyl guest carrying benzothiadiazole units, demonstrating guest-to-capsule and capsule-to-guest chirality transfer. The induced chirality on the bound guest enables it to emit circularly polarized luminescence in the NIR region, demonstrating the application of induced chirality for confined spaces for the generation of chiroptical properties.

Herein, chiral metal-organic frameworks (MOFs), DCF-20 and LCF-20, were utilized as matrices for both chirality transfer and energy transfer. HBT1@MOFs and HBT2@MOFs emit excitation-dependent circularly polarized luminescence (CPL) due to excited-state intramolecular proton transfer (ESIPT). HBT1/C152/NIR@MOFs exhibit full-color and white CPL. The luminescence dissymmetry factors (glum) were significantly increased, benefiting from the efficient chirality space transfer and high luminescence efficiency.

The orthogonal- or co-assembly of achiral perylene bisimide (PBI) with chiral gelators can be regulated by solvents. While the coassembly leads to the formation of chiroptical nanofibers through chirality transfer, the orthogonal assemblies could not. Moreover, protonation on the coassembled nanofibers could light up the circularly polarized luminescence (CPL).

Molecular motions are closely associated with the behaviors and properties of organic materials. However, monitoring molecular motions is challenging. Herein, a chiral supramolecular system consisting of L-/D-phenylalanine (LPF/DPF) as a chiral inducer and an achiral tetraphenylethene derivative (TPEF) as a molecular rotor has been proposed and explored for real-time discriminating the supramolecular motions by the visualization of circularly polarized luminescence (CPL) signal variations. Derived from the ordered molecular motions of TPEF induced by LPF/DPF, highly organized aggregates have been progressively assembled in a controlled manner with differentiated morphologies, including spherical particles, one-dimensional fibers, and floor-shaped supercrystals. Notably, increasing level of ordered aggregates, in turn, led to quenching emissions, while the CPL signals have been dramatically amplified accompanying by a sharp enhancement of luminescence dissymmetry factors (glum ) from nearly 0 to -0.1. The significant amplification of CPL is attributed to the ordered aggregates of supramolecules, leading to the decrease of electric transition dipole moments in supramolecular system. As a result of the chiral supramolecular motions powered by supramolecular crystallization, the supramolecular motions are conveniently discriminated by visual CPL signal variation with an enhancement of glum value from 0 to -0.1 in real time.