Tunable Circularly Polarized Luminescent Supramolecular Systems: Approaches and Applications

When quantum dots meet blue phase liquid crystal elastomers: visualized full-color and mechanically-switchable circularly polarized luminescence

Polymer-based circularly polarized luminescence (CPL) materials with the advantage of diversified structure, easy fabrication, high thermal stability, and tunable properties have garnered considerable attention. However, adequate and precise tuning over CPL in polymer-based materials remains challenging due to the difficulty in regulating chiral structures. Herein, visualized full-color CPL is achieved by doping red, green, and blue quantum dots (QDs) into reconfigurable blue phase liquid crystal elastomers (BPLCEs). In contrast to the CPL signal observed in cholesteric liquid crystal elastomers (CLCEs), the chiral 3D cubic superstructure of BPLCEs induces an opposite CPL signal. Notably, this effect is entirely independent of photonic bandgaps (PBGs) and results in a high glum value, even without matching between PBGs and the emission bands of QDs. Meanwhile, the lattice structure of the BPLCEs can be reversibly switched via mechanical stretching force, inducing on-off switching of the CPL signals, and these variations can be further fixed using dynamic disulfide bonds in the BPLCEs. Moreover, the smart polymer-based CPL systems using the BPLCEs for anti-counterfeiting and information encryption have been demonstrated, suggesting the great potential of the BPLCEs-based CPL active materials.

Clustering-Triggered Emission Liquid Crystalline Polymer Bearing Cholesterol: Tunable Circularly Polarized Luminescence and Room-Temperature Phosphorescence

Circularly polarized luminescence (CPL) materials with clustering-triggered emission (CTE) characteristic have gradually attracted attention for their unique photophysical properties. However, the majority of reported clusteroluminogens lack chirality and exhibit heterogeneity, making it challenging to achieve a well-defined helical structure necessary for efficient CPL with high dissymmetry factor (glum ). In this paper, chiral liquid crystals are constructed to obtain CTE-based CPL materials with high glum values. Side chain liquid crystal polymer PM6Chol bearing cholesterol clusteroluminogens are designed and synthesized. PM6Chol-coated film and PM6Chol thermal-treated film are also successfully prepared by different film-forming methods. Both the films inherit the CTE characteristic of cholesterol and show excitation wavelength-dependent luminescent behavior. However, the two polymer films exhibit different liquid crystal phase structures, with PM6Chol-coated film being a chiral bilayer smectic C phase and PM6Chol thermal-treated film being an achiral bilayer smectic A phase. Attributed to helical arrangement of cholesterol, PM6Chol-coated film emits efficient CPL with glum values up to 1.0 × 10-1 . For PM6Chol thermal-treated film, no CPL signal is detected due to the absence of helical structure. However, it shows obvious room-temperature phosphorescence with 2.0 s afterglow and 23.9 ms lifetime.

Light-Driven Aqueous Dissipative Pseudorotaxanes with Tunable Fluorescence Enabling Deformable Nano-Assemblies

Developing an artificial dynamic nanoscale molecular machine that dissipatively self-assembles far from equilibrium is fundamentally important but is significantly challenging. Herein, we report dissipatively self-assembling light-activated convertible pseudorotaxanes (PRs) that show tunable fluorescence and enable deformable nano-assemblies. A pyridinium-conjugated sulfonato-merocyanine derivative (EPMEH) and cucurbit[8]uril (CB[8]) form the 2EPMEH ⊂ CB[8] [3]PR in a 2:1 stoichiometry, which phototransforms into a transient spiropyran containing 1:1 EPSP ⊂ CB[8] [2]PR when exposed to light. The transient [2]PR thermally relaxes (reversibly) to the [3]PR in the dark accompanied by periodic fluorescence changes that include near-infrared emission. Moreover, octahedral and spherical nanoparticles are formed through the dissipative self-assembly of the two PRs, and the Golgi apparatus is dynamically imaged using fluorescent dissipative nano-assemblies.

Metallophilic Interactions Drive Supramolecular Chirality Evolution and Amplify Circularly Polarized Luminescence

Metallophilic interactions, which are ubiquitous among d¹⁰ metal complexes with linear coordination geometries, can direct one-dimensional assembly. However, the ability of these interactions to manipulate chirality at the hierarchical level largely remains unknown. In this work, we unveiled the role of Au···Cu metallophilic interactions in directing the chirality of multicomponent assemblies. N-heterocyclic carbene-Au(I) complexes bearing amino acid residues formed chiral co-assemblies with [CuI₂]^- anions via Au···Cu interactions. These metallophilic interactions changed the molecular packing modes of the co-assembled nanoarchitectures from lamellar to columnar chiral packing. This transformation initiated the emergence, inversion, and evolution of supramolecular chirality, thereby affording helical superstructures, depending on the geometry of building units. In addition, the Au···Cu interactions altered the luminescence properties and induced the emergence and amplification of circularly polarized luminescence. This work, for the first time, revealed the role of Au···Cu metallophilic interactions in modulating supramolecular chirality, paving the way for the construction of functional chiroptical materials based on d¹⁰ metal complexes.

Circularly polarized luminescence in molecular recognition systems: Recent achievements

Circularly polarized luminescence (CPL) dyes are recognized to be new generation materials and have been actively developed. Molecular recognition systems provide nice approaches to novel CPL materials, such as stimuli-responsive switches and chemical sensing materials. CPL may be induced simply by mixing chiral or achiral, luminescent or nonluminescent host and guest; there are several combinations. Molecular recognition can potentially save time and effort to construct well-ordered chiral structures with noncovalent attractive interactions as compared with the multi-step synthesis of covalently bonded dyes. It is a challenging subject to engage molecular recognition events with CPL, and it is important and interesting to see how it is achieved. In fact, simple molecular recognition systems can even enable the fine adjustment of CPL performance and detailed conformational/configurational analysis of the excited state. Here we overview the recent achievements of simple host-guest complexes capable of exhibiting CPL, summarizing concisely the host/guest structures, CPL intensities, and characteristics.

Direct observation of long-range chirality transfer in a self-assembled supramolecular monolayer at interface in situ

Due to the interest in the origin of life and the need to synthesize new functional materials, the study of the origin of chirality has been given significant attention. The mechanism of chirality transfer at molecular and supramolecular levels remains underexplored. Herein, we study the mechanism of chirality transfer of N, N'-bis (octadecyl)-_L-_/D-(anthracene-9-carboxamide)-glutamic diamide (_L-_/D-GAn) supramolecular chiral self-assembled at the air/water interface by chiral sum-frequency generation vibrational spectroscopy (chiral SFG) and molecular dynamics (MD) simulations. We observe long-range chirality transfer in the systems. The chirality of C_α-H is transferred first to amide groups and then transferred to the anthracene unit, through intermolecular hydrogen bonds and π-π stacking to produce an antiparallel β-sheet-like structure, and finally it is transferred to the end of hydrophobic alkyl chains at the interface. These results are relevant for understanding the chirality origin in supramolecular systems and the rational design of supramolecular chiral materials.

Synchronous Imaging in Golgi Apparatus and Lysosome Enabled by Amphiphilic Calixarene-Based Artificial Light-Harvesting Systems

Artificial supramolecular light-harvesting systems have expanded various properties on photoluminescence, enabling promising applications on cell imaging, especially for imaging in organelles. Supramolecular light-harvesting systems have been used for imaging in some organelles such as lysosome, Golgi apparatus, and mitochondrion, but developing a supramolecular light-harvesting platform for imaging two organelles synchronously still remains a great challenge. Here, we report a series of lower-rim dodecyl-modified sulfonato-calix[4]arene-mediated supramolecular light-harvesting platforms for efficient light-harvesting from three naphthalene diphenylvinylpyridiniums containing acceptors, Nile Red, and Nile Blue. All of the constructed supramolecular light-harvesting systems possess high light-harvesting efficiency. Furthermore, when the two acceptors are loaded simultaneously in a single light-harvesting donor system for imaging in human prostate cancer cells, organelle imaging in lysosome and Golgi apparatus can be realized at the same time with distinctive wavelength emission. Nile Red receives the light-harvesting energy from the donors, reaching orange emissions (625 nm) in lysosome while Nile Blue shows a near-infrared light-harvesting emission at 675 nm in Golgi apparatus in the same cells. Thus, the light harvesting system provides a pathway for synchronously efficient cell imaging in two distinct organelles with a single type of photoluminescent supramolecular nanoparticles.

Eutectogels as Matrices to Manipulate Supramolecular Chirality and Circularly Polarized Luminescence

Solvent is regarded as a factor in tuning the supramolecular chirality of self-assemblies. Deep eutectic solvents (DESs) show diverse properties in contrast to other common solvents, which are emerging in fabricating functional aggregates and nanoarchitectures. Nevertheless, the emergence and manipulation of supramolecular chirality in DES still remain mysterious. Exploring supramolecular chirality in DES would produce tunable chiroptical materials considering their feasible preparation process and abundant hydrogen bonding sites. In this work, we explored the occurrence and manipulation of supramolecular chirality in DES. Transfer from inherent chiral DES to solutes in either aggregated or monomeric building units is blocked. However, the chiral assembly of π-conjugated amino acids was realized. Compared to aqueous media, self-assembly in DES hinders the spontaneous structural and chirality evolution that benefit from efficient solvation, where the π-conjugated amino acids were involved as hydrogen bonding donors. DES performs as a dye-friendly matrix to afford chiroptical eutectogels with tunable circularly polarized luminescence, whereby a large dissymmetry g-factor of up to 0.015 was realized. DES behaves as feasible and flexible solvents to fabricate and stabilize functional soft chiral self-assemblies with controllable chiroptical properties.

An Artificial Light-Harvesting System with Controllable Efficiency Enabled by an Annulene-Based Anisotropic Fluid

The development of controllable artificial light-harvesting systems based on liquid crystal (LC) materials, i.e., anisotropic fluids, remains a challenge. Herein, an annulene-based discotic LC compound 6 with a saddle-shaped cyclooctatetrathiophene core has been synthesized to construct a tunable light-harvesting platform. The LC material shows a typical aggregation-induced emission, which can act as a suitable light-harvesting donor. By loading Nile red (NiR) as an acceptor, an artificial light-harvesting system is achieved. Relying on the thermal-responsive self-assembling ability of 6 with variable molecular order, the efficiency of such 6-NiR system can be controlled by temperature. This light-harvesting system works sensitively at a high donor/acceptor ratio as 1000 : 1, and exhibits a high antenna effect (39.1) at a 100 : 1 donor/acceptor ratio. This thermochromic artificial light-harvesting LC system could find potential applications in smart devices employing soft materials.

Tunable Circularly Polarized Luminescence with a High Dissymmetry Factor Emitted from Luminogen-Bonded and Electrically Controlled Polymer-Stabilized Cholesteric Liquid Crystals

Circularly polarized luminescence (CPL)-active materials with high dissymmetry factor (g_lum) values show great potential in photonic devices. In this study, electric-field-driven systems with tunable CPL signals are successfully fabricated based on polymer-stabilized cholesteric liquid crystal (PSChLC) doping by fluorescent molecules. By constructing a gradient helical superstructure of PSChLCs, distinctive CPL emission from two sides of a single sample is realized, in which the |g_lum| values were measured to be 0.6 and 1.5, respectively. Herein, we discussed the possible mechanism of this phenomenon. In addition, an applied electric field could broaden the reflection bandwidth of PSChLCs from 150 to 500 nm, covering the whole visible light region. Furthermore, this electric field-induced behavior leads to the variation of CPL signals and corresponding g_lum values, indicating the potential of the novel materials in the design and preparation of CPL-emitting devices with electrically tunable CPL intensity and g_lum.