Dimension-Tunable Circularly Polarized Luminescent Nanoassemblies with Emerging Selective Chirality and Energy Transfer

From individuals to families: design and application of self-similar chiral nanomaterials

Establishing an intimate relationship between similar individuals is the beginning of self-extension. Various self-similar chiral nanomaterials can be designed using an individual-to-family approach, accomplishing self-extension. This self-similarity facilitates chiral communication, transmission, and amplification of synthons. We focus on describing the marriage of discrete cages to develop self-similar extended frameworks. The advantages of utilizing cage-based frameworks for chiral recognition, enantioseparation, chiral catalysis and sensing are highlighted. To further promote self-extension, fractal chiral nanomaterials with self-similar and iterated architectures have attracted tremendous attention. The beauty of a fractal family tree lies in its ability to capture the complexity and interconnectedness of a family's lineage. As a type of fractal material, nanoflowers possess an overarching importance in chiral amplification due to their large surface-to-volume ratio. This review summarizes the design and application of state-of-the-art self-similar chiral nanomaterials including cage-based extended frameworks, fractal nanomaterials, and nanoflowers. We hope this formation process from individuals to families will inherit and broaden this great chirality.

Flexible Full-Inorganic Ultrathin Films with Stable Circularly Polarized Luminescence Covering the Visible to Near-Infrared Region

Circularly polarized luminescence (CPL) materials hold significant value in various fields, including information storage, secure communication, three-dimensional displays, biological detection, and optoelectronic devices. Using the Langmuir-Schaeffer (LS) assembly technique, we successfully construct a series of large-area flexible optical ultrathin films. Impressively, the inorganic assembled ultrathin films exhibit excellent CPL optical activity covering the visible to near-infrared (NIR) region, with the luminescence asymmetry factor glum ranging from 0.59 to 0.72. Moreover, such ultrathin films also display outstanding mechanical flexibility, the optical activity of which even after 240 bending cycles shows almost no difference compared to the unbent samples. Owing to the ultra-broadband optical activity and ultra-stable optical activity of such full-inorganic assembled materials on flexible substrates, coupled with their excellent processability and outstanding mechanical flexibility, we anticipate they will find use in many fields such as communication technology and flexible optoelectronics.

Precise Modulation of Circularly Polarized Luminescence via Polymer Chiral Co-assembly and Contactless Dynamic Chiral Communication

Circularly polarized luminescence (CPL) plays a pivotal role in cutting-edge display and information technologies. Currently achieving precise color control and dynamic signal regulation in CPL still remains challenging due to the elusory relationship between fluorescence and chirality. Inspired by the natural mechanisms governing color formation and chiral interaction, we proposed an addition-subtraction principle theory to address this issue. Three fluorene-based polymers synthesized by Suzuki polycondensation with different electron-deficient monomers exhibit similar structures and UV/Vis absorption, but distinct fluorescence emissions due to intramolecular charge transfer. Based on this, precise-color CPL-active films are obtained through quantitative supramolecular co-assembly directed by addition principle. Particularly, an ideal white-emitting CPL film (CIE coordinates: (0.33, 0.33)) is facilely fabricated with a high quantum yield of 80.8 % and a dissymmetry factor (glum) of 1.4×10-2. Structural analysis reveals that the ordered stacking orientation favors higher glum. Furthermore, to address the dynamically regulated challenge, the comparable subtraction principle is proposed, involving a contactless chiral communication between excited and ground states. The representative system consisting of as-prepared fluorene-based polymers and chirality-selective absorption azobenzene (Azo)-containing polymers is constructed, achieving CPL weakening, reversal, and enhancement. Finally, a switchable quick response code is realized based on trans-cis isomerization of Azo moiety.

Enabling robust blue circularly polarized organic afterglow through self-confining isolated chiral chromophore

Creating circularly polarized organic afterglow system with elevated triplet energy levels, suppressed non-radiative transitions, and effective chirality, which are three critical prerequisites for achieving blue circularly polarized afterglow, has posed a formidable challenge. Herein, a straightforward approach is unveiled to attain blue circularly polarized afterglow materials by covalently self-confining isolated chiral chromophore within polymer matrix. The formation of robust hydrogen bonds within the polymer matrix confers a distinctly isolated and stabilized molecular state of chiral chromophores, endowing a blue emission band at 414 nm, lifetime of 3.0 s, and luminescent dissymmetry factor of ~ 10-2. Utilizing the synergistic afterglow and chirality energy transfer, full-color circularly polarized afterglow systems are endowed by doping colorful fluorescent molecules into designed blue polymers, empowering versatile applications. This work paves the way for the streamlined design of blue circularly polarized afterglow materials, expanding the horizons of circularly polarized afterglow materials into various domains.

Discriminatory fluorescence and FRET in the chiral-perovskite/RhB system

Förster resonance energy transfer (FRET) holds a significant position in various natural and artificial systems, especially within donor-acceptor systems encompassing chiral components. Despite extensive investigations, a clear understanding of the effects of chirality and FRET on discriminatory fluorescence remains elusive. Here, chiral perovskite nanowires (CPNWs) and achiral rhodamine B (RhB) are employed to examine the FRET and discriminatory fluorescence behavior in a donor-acceptor system involving a chiral nanostructure. A notable FRET from the CPNWs to RhB is observed, along with circular dichroism (CD) and circularly polarized luminescence (CPL) activities in RhB. Although the FRET interaction remains consistent over time, a notable inversion in the polarity preference of the CD and CPL of RhB is observed. This reveals that the discriminatory fluorescence of the acceptor arises from the electromagnetic influence of the chiral donor. These findings elucidate that "chirality", as a property related to spatial orientation, cannot accompany the transfer of energy (which is a scalar) from chiral nanostructures to achiral molecules, which helps advance the understanding of the discriminatory fluorescence in the donor-acceptor system with a chiral nanostructure.

Red Circularly Polarized Luminescence from Dimeric H-Aggregates of Acridine Orange by Chiral Induction

Understanding the mechanism of chirality transfer from a chiral surface to an achiral molecule is essential for designing molecular systems with tunable chiroptical properties. These aspects are explored herein using l- and d-isomers of alkyl valine amphiphiles, which self-assemble in water as nanofibers possessing a negative surface charge. An achiral chromophore, acridine orange, upon electrostatic binding on these surfaces displays mirror-imaged bisignated circular dichroism and red-emitting circularly polarized luminescence signals with a high dissymmetry factor. Experimental and computational investigations establish that the chiroptical properties emerge from surface-bound asymmetric H-type dimers of acridine orange, further supported by fluorescence lifetime imaging studies. Specifically, atomistic molecular dynamics simulations show that the experimentally observed chiral signatures have their origin in van der Waals interactions between acridine orange dimers and the amphiphile head groups as well as in the extent of solvent exposure of the chromophore.

Using a molecular additive to control chiral supramolecular assembly and the subsequent chirality transfer process

Hierarchical assembly of chiral molecules is achieved through the introduction of molecular additives, which enables the chiral assembly of nanosheets into helical nanorods with inverted chirality. Moreover, the hierarchical assembly of chiral molecules in the presence of a molecular additive can lead to the subsequent chirality transfer from a molecular system to nanoparticle assemblies.

Circularly Polarized Luminescence Switching Driven by Precisely Tuned Supramolecular Interactions: From Hydrogen Bonding to π-π Interaction

It is highly challenging to achieve circularly polarized luminescence (CPL) switching by precisely tuning supramolecular interactions and unveiling the mechanism of supramolecular chirality inversion. Herein, we demonstrated CPL switching based on diethyl l-glutamate-9-cyanophenanthrene (LGCP) and diethyl l-glutamate-pyrene (LGP) via the precise regulation of supramolecular interactions. LGCP assembly driven by hydrogen bonding showed right CPL, while LGP assembly driven by π-π interaction led to left CPL. Remarkably, significant CPL switching was observed from the assemblies of LGCP/octafluoronaphthalene (OFN), attributed to the alteration of the dominating interaction from weak hydrogen bonding to rather strong π-π interaction, while the assemblies of LGP/OFN exhibited minimum CPL variation because the dominating π-π interaction within the assembly of LGP/OFN illustrated quite limited variations upon arene-perfluoroarene interaction. This work provides a feasible strategy toward the efficient modulation of the chiroptical properties of multiple component supramolecular systems, meanwhile offering possibilities for the mechanism exploration of the chirality inversion of supramolecular assemblies.

Reversible Inversion of Circularly Polarized Luminescence in a Coassembly Supramolecular Structure with Achiral Sulforhodamine B Dyes

The dynamic control of circularly polarized luminescence (CPL) has far-reaching significance in optoelectronics, information storage, and data encryption. Herein, we reported the reversible inversion of CPL in a coassembly supramolecular system consisting of chiral molecules L4, which contain two positively charged viologen units, and achiral ionic surfactant sodium dodecyl sulfate (SDS) by introducing achiral sulforhodamine B (SRB) dye molecules. The chirality of CPL in the coassemblies can be efficiently regulated and inverted by simply adjusting the amount of SRB. A series of experimental characterization, including optical spectroscopy, electron microscope, ¹H NMR, and X-ray scattering measurements, suggested that SRB could coassemble with L4/SDS to establish a new stable L4/SDS/SRB supramolecular structure through electrostatic interactions. Moreover, the negative-sign CPL could revert to the positive-sign CPL if titanium dioxide (TiO₂) nanoparticles were used to decompose SRB molecules. The evolution of the CPL inversion process could be cycled at least 5 times without a significant decline in CPL signals when SRB was refueled to the system. Our results provide a facile approach to dynamically regulating the handedness of CPL in a multiple-component supramolecular system via achiral species.

Structurally Induced Chirality of an Achiral Chromophore on Self-Assembled Nanofibers: A Twist Makes It Chiral

The surface domains of self-assembled amphiphiles are well-organized and can perform many physical, chemical, and biological functions. Here, we present the significance of chiral surface domains of these self-assemblies in transferring chirality to achiral chromophores. These aspects are probed using l- and d-isomers of alkyl alanine amphiphiles which self-assemble in water as nanofibers, possessing a negative surface charge. When bound on these nanofibers, positively charged cyanine dyes (CY524 and CY600), each having two quinoline rings bridged by conjugated double bonds, show contrasting chiroptical features. Interestingly, CY600 displays a bisignated circular dichroic (CD) signal with mirror-image symmetry, while CY524 is CD silent. Molecular dynamics simulations reveal that the model cylindrical micelles (CM) derived from the two isomers exhibit surface chirality and the chromophores are buried as monomers in mirror-imaged pockets on their surfaces. The monomeric nature of template-bound chromophores and their binding reversibility are established by concentration- and temperature-dependent spectroscopies and calorimetry. On the CM, CY524 displays two equally populated conformers with opposite sense, whereas CY600 is present as two pairs of twisted conformers in each of which one is in excess, due to differences in weak dye-amphiphile hydrogen bonding interactions. Infrared and NMR spectroscopies support these findings. Reduction of electronic conjugation caused by the twist establishes the two quinoline rings as independent entities. On-resonance coupling between the transition dipoles of these units generates bisignated CD signals with mirror-image symmetry. The results presented herein provide insight on the little-known structurally induced chirality of achiral chromophores through transfer of chiral surface information.

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.

Diffusion-mediated carving of interior topologies of all-natural protein nanoparticles to tailor sustained drug release for effective breast cancer therapy

Proteins are promising base materials for developing drug carriers with efficient blood circulation due to low possibilities of clearance by macrophages. However, such natural biopolymers have highly sophisticated molecular structures, preventing them from being assembled into nano-platforms with manipulable payload release profiles. Here, we report the self-assembly of two natural proteins (milk casein and rice protein) into protein nanoparticles (NPs, ∼150 nm) with tailorable release profiles. Diffusion of plant-derived paclitaxel (PTX)-containing eugenol into the hydrophobic cores of the NPs and subsequent dialysis to remove eugenol from the cores lead to the carving of the NP interiors. With the increase in the mass ratios of casein and rice protein, this process generates all-natural NPs with PTX loaded in their full cavities, semi-full cavities, or solid cores. These NPs can be efficiently uptaken by breast cancer cells and could kill the cancer cells efficiently. PTX in these NPs demonstrates increasingly sustained in vivo release profiles from full cavities, semi-full cavities, to solid cores, gradually extending its pharmacokinetic profiles in blood plasma to favor drug accumulation in breast tumor models. Consequently, the NPs with solid cores completely inhibit tumor growth in vivo, more effectively than those with full and semi-full cavities. Our work opens up a new avenue to the use of diffusion-mediated nanoscale carving in producing biomaterials with controllable interior topologies relevant to drug release profiles.

Assembly of Helical Nanostructures: Solvent-Induced Morphology Transition and Its Effect on Cell Adhesion

Being able to precisely manipulate both the morphology and chiroptical signals of supramolecular assemblies will help to better understand the natural biological self-assembly mechanism. Two simple l/d-phenylalanine-based derivatives (L/DPFM) have been designed, and their solvent-dependent morphology evolutions are illustrated. It was found that, as the content of H₂ O in aqueous ethanol solutions was increased, LPFM self-assembles first into right-handed nanofibers, then flat fibrous structures, and finally inversed left-handed nanofibers. Assemblies in ethanol and H₂ O exhibit opposite conformations and circular dichroism (CD) signals even though they are constructed from the same molecules. Thus, the morphology-dependent cell adhesion and proliferation behaviors are further characterized. Left-handed nanofibers are found to be more favorable for cell adhesion than right-handed nanostructures. Quantitative AFM analysis showed that the L929 cell adhesion force on left-handed LPFM fibers is much higher than that on structures with inversed handedness. Moreover, the value of cell Young's modulus is lower for left-handed nanofibrous films, which indicates better flexibility. The difference in cell-substrate interactions might lead to different effects on cell behavior.

Designs and Applications of Multi-stimuli Responsive FRET Processes in AIEgen-Functionalized and Bi-fluorophoric Supramolecular Materials

Materials capable of displaying strong ratiometric fluorescence with Förster resonance energy transfer (FRET) processes have attracted much research interest because of various chemosensor and biomedical applications. This review highlights several popular strategies in designing FRET-OFF/ON mechanisms of ratiometric fluorescence systems. In particular, the developments of organic and polymeric FRET materials featuring aggregation-induced emission-based luminogens (AIEgens), supramolecular assemblies, photochromic molecular switches and surfactant-induced AIE/FRET mechanisms are presented. AIEgens have been frequently employed as FRET donor and/or acceptor fluorophores to obtain enhanced ratiometric fluorescences in solution and solid states. Since AIE effects and FRET processes rely on controllable distances between fluorophores, many interesting fluorescent properties can be designed by regulating aggregation states in polymers and supramolecular systems. Photo-switchable fluorophores, such as spiropyran and diarylethene, provide drastic changes in fluorescence spectra upon photo-induced isomerizations, leading to photo-switching mechanisms to activate/deactivate FRET processes. Supramolecular assemblies offer versatile platforms to regulate responsive FRET processes effectively. In rotaxane structures, the donor-acceptor distance and FRET efficiency can be tuned by acid/base-controlled shuttling of the macrocycle component. The tunable supramolecular interactions are strongly influenced by external factors (such as pH values, temperatures, analytes, surfactants, UV-visible lights, etc.), which induce the assembly and disassembly of host-guest systems and thus their FRET-ON/FRET-OFF behavior. In addition, the changes in donor or acceptor fluorescence profiles upon detections of analytes can also sufficiently alter the FRET behavior and result in different ratiometric fluorescence outputs. The strategies and examples provided in this review offer the insights and toolkits for future FRET-based material developments.

Circularly Polarized Photoluminescence of Chiral 2D Halide Perovskites at Room Temperature

Chiral halide perovskites have attracted considerable attention because of their chiroptical, second-harmonic generation, and ferroelectricity properties and their potential application in chiroptoelectronics and chiral spintronics. However, the fundamental research of these properties is insufficient. In this work, chiral perovskites were synthesized using precursor solutions with various stoichiometric ratios ⟨n⟩. The chiral perovskite film prepared from the solution with ⟨n⟩ = 1 is composed of (R-/S-/rac-MBA)₂PbBr₄, whereas the films prepared from the solutions with ⟨n⟩ larger than 1 are a mixture of (R-/S-/rac-MBA)₂(CsMA)_n-1Pb_nBr_3n+1 with n = 1 and large n values. A photoluminescence quantum yield of approximately 90 was obtained. Symmetric circular dichroism (CD) spectra were observed without an external magnetic field. Under various magnetic fields, magnetic field-induced CD features are superimposed with the intrinsic chirality-induced CD features. For the ⟨n⟩ = 1 chiral perovskite film, the energy level splitting induced by chiral molecules are a few 10 μeV, whereas the energy level splitting induced by magnetic fields are at the range of ∼-250 to ∼250 μeV. Circularly polarized photoluminescence spectra were observed at room temperature and associated with the spin-preserved energy funneling from highly energetic phases to the lower energetic phases.

Switchable Circularly Polarized Signals with High Asymmetric Factor Triggered by Dual Photonic Bandgap Structure

Currently, the smart photonic materials that can switch circularly polarized signals in real-time have attracted extensive attention due to numerous potential applications in information storage and photonics displays. However, the dynamically reversible switching of circularly polarized signals requires precise structural reconfiguration, which is rarely achieved in traditional biomaterials. Herein, a dual photonic bandgap (PBG) structure is constructed based on the optical propagation principle of cellulose-based photonic crystals, enabling the flexible switching of the intensity, wavelength, and direction of circularly polarized luminescence (CPL). By adjusting the fluorescence intensity and the matching degree of chiral structure, the asymmetric factor value of dual PBG structure is up to -1.47, far exceeding other cellulose-based materials. Importantly, it is demonstrated that dual CPL emission can be efficiently induced by two different PBGs, opening a new approach for on-demand switching of single and dual CPL emission. In addition, the dual PBG structure exhibits dual circularly polarized reflected signals under the circular polarizer, which perfectly embodies the applicability of multiple encryptions in QR codes. This work provides new insights into the real-time manipulation of circularly polarized signals by chiral photonic materials.

Chiral Inversion and Recovery of Supramolecular Luminescent Copper Nanocluster Hydrogels Triggered by Polyethyleneimine and Polyoxometalates

Construction of controllable chiroptical supramolecular luminescence systems is of great significance for developing intelligent chiral luminescence materials with precise and effective regulation and understanding chirality-switching phenomena in biological systems, which has attracted extensive attention. Because chiral metal nanoclusters (NCs) can provide facilities for the study of nanoscale chiral effects, in this study, we select chiral glutathione-stabilized copper NCs (G-SH-Cu NCs) to construct a supramolecular luminescent hydrogel with achiral branched polyethyleneimine (PEI) and polyoxometalates [Na₉(EuW₁₀O₃₆)·32H₂O, denoted as EuW₁₀]. Thus, a chiral property precise controlled system was constructed by self-assembly. Interestingly, the addition of PEI to G-SH-Cu NC solution induced the formation of luminescent hydrogels with chiral inversion, while further addition of EuW₁₀ not only enhanced the luminescence of the hydrogel but also recovered the chiroptical properties. The chiral inversion behavior is possibly ascribed to the hydrogen bond interaction/electrostatic interaction between G-SH-Cu NCs and PEI in the chiral inversion process, while the competition of hydrogen bonding interaction (between G-SH-Cu NCs and PEI) and electrostatic interaction (between PEI and EuW₁₀) was accountable for the chiral recovery process. Manipulation of chirality inversion in the metal NC-containing coassemblies is rare, while this work establishes a feasible strategy to modulate the chiral inversion behavior of Cu NCs, which not only produces new physicochemical properties of metal NCs through synergistic behavior but also offers a feasible way to realize the potential application of chiroptical materials.

Tunable Circularly Polarized Luminescence via Chirality Induction and Energy Transfer from Organic Films to Semiconductor Nanocrystals

Circularly polarized luminescent (CPL) films with high dissymmetry factors hold great potential for optoelectronic applications. Herein, we propose a strategy for achieving strongly dissymetric CPL in nanocomposite films based on chirality induction and energy transfer to semiconductor nanocrystals. First, focusing on a purely organic system, aggregation-induced emission (AIE) and CPL activity of organic liquid crystals (LCs) forming helical nanofilaments was detected, featuring green emission with high dissymmetry factors g_lum ∼ 10^-2. The handedness of helical filaments, and thus the sign of CPL, was controlled via minute amounts of a small chiral organic dopant. Second, nanocomposite films were fabricated by incorporating InP/ZnS semiconductor quantum dots (QDs) into the LC matrix, which induced the chiral assembly of QDs and endowed them with chiroptical properties. Due to the spectral matching of the components, energy transfer (ET) from LC to QDs was possible enabling a convenient way of tuning CPL wavelengths by varying the LC/QD ratio. As obtained, composite films exhibited absolute g_lum values up to ∼10^-2 and thermally on/off switchable luminescence. Overall, we demonstrate the induction of chiroptical properties by the assembly of nonchiral building QDs on the chiral organic template and energy transfer from organic films to QDs, representing a simple and versatile approach to tune the CPL activity of organic materials.

Signal Inversion and Amplification of Circularly Polarized Luminescence in a Poly(phenylacetylene)-Based Composite System Assisted by Achiral PMMA

Multichannel regulable circularly polarized luminescence (CPL) is fascinating because of its fundamental and application interest. There are few reports on helical sense (P-/M-helix) modulation and chiral signal amplification of polyacetylenes with the assistance of achiral polymers and further applications in precisely and conveniently regulating CPL handedness and magnitude. Herein, a helical poly(phenylacetylene)-based CPL-active system was constructed, in which CPL inversion occurred by adding achiral PMMA into a helical poly(phenylacetylene)-CHCl₃ solution. Significantly, there is almost 10 times magnification of luminescence dissymmetry factor values (|g_lum|) during this process. The above phenomena could be ascribed to the PMMA-assisted polyene backbone elongation and the formation of a more ordered helical structure for the poly(phenylacetylene)s. More interestingly, the CPL signal can be facilely inverted and switched by simply changing the thickness of the PPhAD/PMMA layer. The temperature-driven dynamic CPL handedness inversion and magnitude modulation can also be achieved. Based on the multiple regulations for CPL, logic operations were developed, and the practical application is further facilitated by designing various CPL patterns. This study establishes effective and convenient strategies to switch the handedness, magnitude, and wavelength of CPL, which may generate a breakthrough in the manufacturing of CPL-active smart materials and devices with promising application potential.

Morphology-dependent photoresponsive behaviors of a self-assembled system based on a single cyanostilbene derivative

In recent years, photoresponsive supramolecular self-assemblies have shown great potential in various fields. However, it is still a great challenge to integrate and control multiple photoresponsive behaviors in a self-assembled system. Herein, we design a novel cyanostilbene-based molecule VOE. In the aggregated state, it has different photoresponsive behaviors under different morphologies. When VOE molecules are dispersed in a 70% H₂O/THF mixture, two different assembly morphologies are obtained as the aging time changes. One is weakly emissive nanoparticles with amorphous packing arrangements, and the other is highly emissive microbelts with well-ordered stacking modes. When they are irradiated with blue light (420 nm), the disordered assembly structure of nanoparticles leads to a [2+2] cycloaddition reaction, while a Z/E isomerization reaction occurs in ordered packed microbelts. Therefore, we can use a self-assembled system to generate two different morphologies, enabling completely different emissions and photoresponsive behaviors.

Optical Polarization-Based Measurement Methods for Characterization of Self-Assembled Peptides' and Amino Acids' Micro- and Nanostructures

In recent years, self-assembled peptides’ and amino acids’ (SAPA) micro- and nanostructures have gained much research interest. Here, description of how SAPA architectures can be characterized using polarization-based optical measurement methods is provided. The measurement methods discussed include: polarized Raman spectroscopy, polarized imaging microscopy, birefringence imaging, and fluorescence polarization. An example of linear polarized waveguiding in an amino acid Histidine microstructure is discussed. The implementation of a polarization-based measurement method for monitoring peptide self-assembly processes and for deriving molecular orientation of peptides is also described.

Arene-perfluoroarene interaction induced chiroptical inversion and precise ee% detection of chiral acids in a benzimidazole-involved ternary coassembly

Flexible regulation of chirality and handedness of chiral functional materials and quantitative sensing of natural chiral compounds remains a considerable challenge. Herein, an achiral fluorescent 1-pyrenecarboxylic acid-benzimidazole derivative (PBI) was synthesized and its chiroptical properties upon coassembly with chiral acids (TA and MA) and octafluoronaphthalene (OFN) through hydrogen bonds between benzimidazole and chiral acids as well as an arene-perfluoroarene (AP) interaction between a pyrene moiety and OFN were systemically studied. The binary assemblies of PBI/TA and PBI/MA displayed opposite chiroptical properties including circular dichroism (CD) and circularly polarized luminescence (CPL) signals. Interestingly, the handedness of CPL was further inverted in ternary assemblies due to the synergistic effect of the AP interaction and hydrogen bonds. Besides, the highly accurate chiral sensing of chiral acids via binary assemblies was successfully achieved with a high correlation coefficient. This work provides a simple method for regulating the handedness of chiroptical active materials and quantitative sensing of chiral acids through orthogonal multiple component coassemblies.

Single-component color-tunable circularly polarized organic afterglow through chiral clusterization

Circularly polarized organic afterglow (CPOA) with both long-lived room-temperature phosphorescence (RTP) and circularly polarized luminescence (CPL) is currently attracting great interest, but the development of multicolor-tunable CPOA in a single-component material remains a formidable challenge. Here, we report an efficient strategy to achieve multicolor CPOA molecules through chiral clusterization by implanting chirality center into non-conjugated organic cluster. Owing to excitation-dependent emission of clusters, highly efficient and significantly tuned CPOA emissions from blue to yellowish-green with dissymmetry factor over 2.3 × 10-3 and lifetime up to 587 ms are observed under different excitation wavelengths. With the distinguished color-tunable CPOA, the multicolor CPL displays and visual RTP detection of ultraviolent light wavelength are successfully constructed. These results not only provide a new paradigm for realization of multicolor-tunable CPOA materials in single-component molecular systems, but also offer new opportunities for expanding the applicability of CPL and RTP materials for diversified applications.

Hierarchical self-assembly into chiral nanostructures

One basic principle regulating self-assembly is associated with the asymmetry of constituent building blocks or packing models. Using asymmetry to manipulate molecular-level devices and hierarchical functional materials is a promising topic in materials sciences and supramolecular chemistry. Here, exemplified by recent major achievements in chiral hierarchical self-assembly, we show how chirality may be utilized in the design, construction and evolution of highly ordered and complex chiral nanostructures. We focus on how unique functions can be developed by the exploitation of chiral nanostructures instead of single basic units. Our perspective on the future prospects of chiral nanostructures via the hierarchical self-assembly strategy is also discussed.

Chiral macrocycle-induced circularly polarized luminescence of a twisted intramolecular charge transfer dye

The host-guest binding between a chiral macrocycle and an achiral dye could suppress the twisted intramolecular charge transfer (TICT) process, leading to enhanced emission and bright circularly polarized luminescence (CPL) from the originally achiral TICT-dye.

Chiral Self-Assembled Film from Semiconductor Nanorods with Ultra-Strong Circularly Polarized Luminescence

Chiroptical nanomaterials have generated significant levels of interest for generating strong circularly polarized luminescence (CPL) signals. We used the Langmuir-Schaeffer technique to generate the continuous and compact assembly of CdSe/CdS chiral film. We assembled achiral CdSe/CdS nanorods by controlling the number of layers and angles between different layers. This allowed us to tailor chiroptical properties to achieve high CPL signals. The chiral film was symmetrical and had the highest circular dichroism (CD) response and CPL signals with ten layers (RH (right-handed)-/LH (left-handed)-5 + 5 layers) and a 45° inter-angle. Specifically, RH-5+5 of the chiral film exhibited 1431 mdeg of CD activity and strong CPL signals with a dissymmetry factor (glum) of 0.0997. The helical stacked crystal plates with linear birefringence resulted in strong circular birefringence, as determined by the Reusch model. Electromagnetic simulations indicated that such remarkable optical activity was attributed to the birefringence and dichroism of the well-aligned CdSe/CdS nanorod layers in the chiral films. Under right/left circular polarized (RCP/LCP) light excitation, the well aligned semiconductor nanorods exhibited differences in the coupling efficiencies to RCP and LCP light. Our CdSe/CdS chiral films, which exhibit ultra-strong CPL activity, will provide a novel strategy for the fabrication of chiroptical devices.

Multilevel Chirality Transfer from Amino Acid Derivatives to Circularly Polarized Luminescence-Active Nanoparticles in Aqueous Medium

Chirality at different levels is widely observed in nature, but the clue to connect it all together, and the way chirality transfers among different levels are still obscure. Herein, a l-/d-lysine-based self-assembly system was constructed, in which two-step chirality transfer among three different levels was observed in aqueous solution. The chirality originated from the point chirality of amino acid derivatives l-/d-PyLys hydrochloride, and was transferred to the planar conformational chirality of water-soluble pillar[5]arene pR-/pS-WP5. Then, with the aid of pR-/pS-WP5, nanoparticles were formed that exhibited L-/R-handed circularly polarized luminescence with a dissymmetry factor of up to ±0.001, arising from pyrene chiral excimers. This multilevel chirality transfer not only provides a perspective to trace potential clues, and to pursue certain ways by which the chirality transfers, but also offers a strategy to create controllable CPL emission in aqueous media.

Self-Assembly and Circularly Polarized Luminescence from Achiral Pyrene-Adamantane Conjugates by Selective Inclusion with Cyclodextrins

The interaction between guest chromophores or lumiphores with host chiral cavity and their induced chirality is an important topic in supramolecular chemistry. Kodaka and Harata proposed a rule to explain the induced circular dichroism of the guest chromophores by host cyclodextrins. However, it remains unknown how a circularly polarized luminescence (CPL) signal will change when the lumiphores interacted with cyclodextrins in different modes. Here, we designed an achiral pyrene-adamantane conjugated guest molecule, N-(pyren-1-yl)adamantane-1-carboxamide (ACNP), and investigated its interactions with α/β/γ-cyclodextrins (CDs) and its induced CPL. Depending on the size match of the pyrene, adamantine with different cyclodextrins, distinct performance was observed. While α-CD could not induce a CPL signal of ACNP, β-CD could induce CPL in two modes, through adamantyl or direct pyrenyl induction, which could produce a CPL signal with opposite signs. γ-CD could always induce a negative CPL signal. Therefore, a rule of induced CPL of lumiphores by cyclodextrins can be proposed.

Circularly polarized luminescence from organic micro-/nano-structures

Circularly polarized light exhibits promising applications in future displays and photonic technologies. Circularly polarized luminescence (CPL) from chiral luminophores is an ideal approach to directly generating circularly polarized light, in which the energy loss induced by the circularly polarized filters can be reduced. Among various chiral luminophores, organic micro-/nano-structures have attracted increasing attention owing to the high quantum efficiency and luminescence dissymmetry factor. Herein, the recent progress of CPL from organic micro-/nano-structures is summarized. Firstly, the design principles of CPL-active organic micro-/nano-structures are expounded from the construction of micro-/nano-structure and the introduction of chirality. Based on these design principles, several typical organic micro-/nano-structures with CPL activity are introduced in detail, including self-assembly of small molecules, self-assembly of π-conjugated polymers, and self-assembly on micro-/nanoscale architectures. Subsequently, we discuss the external stimuli that can regulate CPL performance, including solvents, pH value, metal ions, mechanical force, and temperature. We also summarize the applications of CPL-active materials in organic light-emitting diodes, optical information processing, and chemical and biological sensing. Finally, the current challenges and prospects in this emerging field are presented. It is expected that this review will provide a guide for the design of excellent CPL-active materials.

Ultrastrong Red Circularly Polarized Luminescence Promoted from Chiral Transfer and Intermolecular Förster Resonance Energy Transfer in Ternary Chiral Emissive Nematic Liquid Crystals

Chiral emissive liquid crystals (N*-LCs) have been proved to greatly amplify the circularly polarized luminescence (CPL) signals due to highly regular spiral arrangement of dyes in a well-organized liquid crystals system. Normally, CPL materials with a high luminescence dissymmetry factor (g_lum) and quantum yield (QY) can meet the real application requirement. Here, four chiral aggregate-induced emission (AIE) active donors (Guests A1-A4: R-C2, R-C4, R-C6, R-C8, chiral dopant, and energy donor) and achiral AIE-active acceptors (Guest B: PBCy, CPL emitter) were doped into the commercial nematic liquid crystals E7 (N-LCs, Host) to form CPL-active ternary chiral emissive N-LCs (T-N*-LCs), respectively. This kind of T-N*-LCs could emit strong red CPL with QY = 16.56% and g_lum up to 1.51 through intermolecular energy transfer and chirality induction from the supramolecular self-assembly of T-N*-LCs. This work provides the effective strategy for the development of high g_lum CPL materials.

Strong-Induced CPL Emission Promoted from Achiral Conjugated Polymer-Containing Emissive Nematic Liquid Crystals (P-N*-LCs)

With the rapid development on 3D printing technology, more and more works have been devoted to 3D display. 3D display will really come true by using circularly polarized luminescence (CPL)-active materials with both high quantum yield and dissymmetry factor (g_em ) in organic light-emitting diode or liquid crystals (LCs). But so far most of these CPL materials cannot meet the real application requirement because of the low g_em values in the range of 10^-5 -10^-2 . In this paper, ternary chiral emissive LCs (P-N*-LCs) is designed by doping chiral binaphthyl-based enantiomers as chiral dopant (Guest 1) and achiral conjugated polymer as induced CPL emitter (Guest 2) into nematic liquid crystal (N-LCs) Host 5CB. Both Guest 1 and Guest 2 show excellent compatibility with Host 5CB. The obtained ternary P-N*-LCs can emit strong-induced CPL signal with g_em up to 1.12 and Ф_FL up to 66.1%. This work first develops a new strategy for the smart design of excellent CPL materials from versatile achiral conjugation fluorescence polymers.

Circularly polarized luminescence of nanoassemblies via multi-dimensional chiral architecture control

Circularly polarized luminescence (CPL) materials are currently an important class of chiroptical materials that are attracting increasing interest. Nanoassemblies constructed from chiral or achiral building blocks show great potential for achieving CPL-active nanomaterials with high quantum yields and dissymmetry factors, which is crucial for further applications. In nanoassemblies, the dimensional morphology affects the chiroptical properties significantly since the microscopic packing modes will affect the luminescence processes and chirality transfer processes. In this review, we will show some examples for illustrating the relationship between multi-dimensional morphology and chiroptical properties. Furthermore, with dimensional morphology tuning, higher dissymmetry factors would be obtained. We hope to provide a useful and powerful insight into the design and control of CPL-active nanoassemblies via morphology control.

Enantiomeric MOF Crystals Using Helical Channels as Palettes with Bright White Circularly Polarized Luminescence

The host-guest chemistry of metal-organic frameworks (MOFs) has enabled the derivation of numerous new functionalities. However, intrinsically chiral MOFs (CMOFs) with helical channels have not been used to realize crystalline circularly polarized luminescence (CPL) materials. Herein, enantiomeric pairs of MOF crystals are reported, where achiral fluorophores adhere to the inner surface of helical channels via biology-like H-bonds and hence inherit the helicity of the host MOFs, eventually amplifying the luminescence dissymmetry factor (g_lum ) of the host l/d-CMOF (±1.50 × 10^-3 ) to a maximum of ±0.0115 for the composite l/d-CMOF⊃fluorophores. l/d-CMOF⊃fluorophores in pairs generate bright color-tunable CPL and almost ideal white CPL (0.33, 0.32) with a record-high photoluminescence quantum yield of ≈30%, which are further assembled into a white circularly polarized light-emitting diode. The present strategy opens a new avenue for propagating the chirality of MOFs to realize universal chiroptical materials.

Spiranthes sinensis-Inspired Circular Polarized Luminescence in a Solid Block Copolymer Film with a Controllable Helix

Chiral materials with circular polarized luminescence (CPL) have attracted much interest because of their extensive optical information and remarkable sensitivity. Inspired by the helical template in Spiranthes sinensis, we propose here a general and flexible method for fabricating solid CPL materials using a block copolymer-formed helix as a template. A chiral arrangement of various nonchiral fluorescent molecules was obtained in the block copolymer-based hybrid film. An excimer chiralty rule was found for the CPL emission of nonchiral fluorescent molecules: a right-handed helix induced left-handed CPL emission and a left-handed helix induced right-handed CPL emission. A dissipative particle dynamics simulation showed that such an antihelical effect is related to the length between the adjacent interacting points of nonchiral fluorescent molecules along the helical structure. Furthermore, the fluorescent films had a high dissymmetric factor for CPL emission, and thus, the films provide a general and flexible platform for designing and preparing advanced functional chiroptical materials.

Helical Nanostructures with Circularly Polarized Luminescence from the Multicomponent Assembly of π-Conjugated N-terminal Amino Acids

Self-assembled structures with circularly polarized luminescence (CPL) have attracted great attention in recent years. π-conjugated N-terminal amino acids with chiral amino acid residues and luminophores are capable of forming self-assembled structures at hierarchical levels, whereby chirality can be transferred to the macroscopic scale with easily modulated CPL properties. Due to the presence of multiple noncovalent binding sites, including hydrogen bonding and aromatic interactions, π-conjugated N-terminal amino acids are emerging core candidates for incorporation into multicomponent self-assembled architectures, accomplishing rational control over supramolecular chirality as well as showing rich chiroptical properties. In this Minireview, we provide a brief summary of multiple-component coassembled systems comprising π-conjugated N-terminal amino acids, small organic species and metal ions. The synthesis of helical structures and manipulation of supramolecular chirality by controlling the self-assembled species is introduced, and the CPL properties of multiple-component π-conjugated N-terminal amino acids are also briefly summarized.