Currently, the development of circularly polarized luminescent (CPL) materials has drawn extensive attention due to the numerous potential applications in optical data storage, displays, backlights ...in 3D displays, and so on. While the fabrication of CPL‐active materials generally requires chiral luminescent molecules, the introduction of the “self‐assembly” concept offers a new perspective in obtaining the CPL‐active materials. Following this approach, various self‐assembled materials, including organic‐, inorganic‐, and hybrid systems can be endowed with CPL properties. Benefiting from the advantages of self‐assembly, not only chiral molecules, but also achiral species, as well as inorganic nanoparticles have potential to be self‐assembled into chiral nanoassemblies showing CPL activity. In addition, the dissymmetry factor, an important parameter of CPL materials, can be enhanced through various pathways of self‐assembly. Here, the present status and progress of self‐assembled nanomaterials with CPL activity are reviewed. An overview of the key factors in regulating chiral emission materials at the supramolecular level will largely boost their application in multidisciplinary fields.
Recent development of circularly polarized luminescent (CPL) materials has aroused extensive attention. The self‐assembly strategy is proposed to address the barriers of tedious syntheses and the restricted substitutes during the development of CPL‐active materials. By highlighting the meritorious findings, the present status and progress in this field are reviewed, with the aim of boosting the development of chiroptical materials.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
By constructing a supramolecular light‐harvesting chiral nanotube in the aqueous phase, we demonstrate a cooperative energy and chirality transfer. It was found that a cyanostilbene‐appended ...glutamate compound (CG) self‐assembled into helical nanotubes exhibiting both supramolecular chirality and circularly polarized luminescence (CPL). When two achiral acceptors, ThT and AO, with different energy bands were co‐assembled with the nanotube, the CG nanotube could transfer its chirality to both of the acceptors. The excitation energy could be transferred to ThT but only be sequentially transferred to AO. During this process, the CPL ascribed to the acceptor could be sequentially amplified. This work provides a new insight into the understanding the cooperative chirality and energy transfer in a chiral supramolecular system, which is similar to the natural light‐harvesting antennas.
On the other hand: When the achiral acceptors thioflavin T (ThT) and acridine orange (AO), with different energy bands, were co‐assembled with the nanotube CG it could transfer its chirality to both of the acceptors to give an enhancement of acceptor circularly polarized luminescence (CPL). The excitation energy could be transferred to ThT but only be sequentially transferred to AO.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Achieving homochirality is challenging both at the molecular and the supramolecular levels. While the origin of molecular homochirality still remains mysterious, the fabrication of homochiral ...assemblies from achiral molecules has attracted considerable interest since it provides many clues to understand the origin of molecular chirality. Here, by using a vortex mixing-accompanied self-assembly strategy, we obtained near-unity homochiral entities with controlled handedness from supramolecular gels that consist of exclusively achiral molecules without any chiral additives. The common supramolecular gelation process
heating and cooling of the achiral molecules only resulted in racemic gels. However, if vortex mixing is applied during the self-assembly, near-unity homochiral assemblies with uncontrolled handedness were obtained. Vortex mixing during the nucleation stage was found to be crucial in this case. On the other hand, if a small amount of the above vortex mixing produced assemblies was added as chiral seeds into the racemic gels, the racemic gels turned into near-unity homochiral suspensions with controlled handedness
a ripening process. Our studies provide an intriguing approach for achieving homochiral supramolecular assemblies from achiral molecules.
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IJS, KILJ, NUK, UL, UM, UPUK
Achieving a higher dissymmetry factor is a crucial issue in developing circularly polarized luminescence (CPL) materials. Here, by tailoring the solvent composition and the morphology of the same ...chiral emissive small molecules (
- or
-SPAn), circularly polarized emission with a boosted dissymmetry factor (two orders) was realized. It was found that by regulating the water fraction in the mixed THF/H
O, we were able to achieve kinetic control over association of chiral emissive
- or
-SPAn into various nanostructures with 0D nanospheres, 2D nanoflakes and 3D stacked nanoflakes. These nanostructures are all CPL active. Remarkably, the dissymmetry factors of the nanostructures were significantly enhanced compared to those of the molecules and further boosted in different morphologies, from ∼10
(0D nanospheres) to 10
(2D flake) to ∼10
(3D nanoflakes). The enlarged
value could be assigned to a good packing induced strong luminescence of an excimer. This strategy provides an efficient way to fabricate higher dissymmetry factor CPL organic nanomaterials by only changing the supramolecular architectures while using the same chiral small molecules.
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Although chirality has been recognized as an essential entity for life, it still remains a big mystery how the homochirality in nature emerged in essential biomolecules. Certain achiral motifs are ...known to assemble into chiral nanostructures. In rare cases, their absolute geometries are enantiomerically biased by mirror symmetry breaking. Here we report the first example of asymmetric catalysis by using a mirror symmetry-broken helical nanoribbon as the ligand. We obtain this helical nanoribbon from a benzoic acid appended achiral benzene-1,3,5-tricarboxamide by its helical supramolecular assembly and employ it for the Cu
-catalyzed Diels-Alder reaction. By thorough optimization of the reaction (conversion: > 99%, turnover number: ~90), the enantiomeric excess eventually reaches 46% (major/minor enantiomers = 73/27). We also confirm that the helical nanoribbon indeed carries helically twisted binding sites for Cu
. Our achievement may provide the fundamental breakthrough for producing optically active molecules from a mixture of totally achiral motifs.
Consecutively boosted circularly polarized luminescence (CPL) with controlled handedness has been demonstrated in a supramolecular assembly from a completely achiral molecule. It is found that ...achiral C 3 symmetric molecules exhibit strong supramolecular chirality as well as CPL through a vortex-accompanied assembly method. Surprisingly, the remarkable chiroptical property and the excited energy of the achiral molecules can be further transferred to another achiral dye, resulting in an amplified CPL with a dissymmetry factor over 0.1. This work not only provides a scenario for realizing the emergence, amplification, and transfer of CPL in the supramolecular system from achiral molecules, but also paves an easy yet efficient way to construct a strong and tunable circularly polarized emission based on the coupling with achiral fluorophores.
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IJS, KILJ, NUK, PNG, UL, UM
Supramolecular gels are currently an important class of soft materials that are attracting great interest. The gelation process has been proven to be a powerful approach for the construction of ...diverse and uniform architectures. Generally, these architectures are on the nanoscale and hierarchically self-assembled from small molecules. Nanoarchitectonics tries to bridge the gap between molecules and nanostructures, while supramolecular gelation provides a good platform to realize such a goal. While the design of the gelator molecules and the function of the gel are important topics, here, we focus on how small molecules can be fabricated into nanostructures through gelation, which is in fact the connection between the microstructures to the macroscopic functions. We showed meritorious examples of typical architectures constructed through the supramolecular gelation process. Then some examples showing the transformation or switching between different nanostructures are presented, which reflected the unique responsiveness of the gel system. Through these two key parts, we hope to provide useful insights into the design and control of functional nanoarchitectures
via
supramolecular gelation.
The formation and switching in gel systems provide supramolecular gelation many possibilities to obtain diverse nanoarchitectures.
The origin of homochirality in life is a fundamental mystery. Symmetry breaking and subsequent amplification of chiral bias are regarded as one of the underlying mechanisms. However, the selection ...and control of initial chiral bias in a spontaneous mirror symmetry breaking process remains a great challenge. Here we show experimental evidences that laminar chiral microvortices generated within asymmetric microchambers can lead to a hydrodynamic selection of initial chiral bias of supramolecular systems composed of exclusively achiral molecules within milliseconds. The self-assembled nuclei with the chirality sign affected by the shear force of enantiomorphic microvortices are subsequently amplified into almost absolutely chirality-controlled supramolecular gels or nanotubes. In contrast, turbulent vortices in stirring cuvettes fail to select the chirality of supramolecular gels. This study reveals that a laminar chiral microflow can induce enantioselection far from equilibrium, and provides an insight on the origin of natural homochirality.
The origin of biological homochirality, e.g., life selects the L-amino acids and D-sugar as molecular component, still remains a big mystery. It is suggested that mirror symmetry breaking plays an ...important role. Recent researches show that symmetry breaking can also occur at a supramolecular level, where the non-covalent bond was crucial. In these systems, equal or unequal amount of the enantiomeric nanoassemblies could be formed from achiral molecules. In this paper, we presented a brief overview regarding the symmetry breaking from dispersed system to gels, solids, and at interfaces. Then we discuss the rational manipulation of supramolecular chirality on how to induce and control the homochirality in the self-assembly system. Those physical control methods, such as Viedma ripening, hydrodynamic macro- and micro-vortex, superchiral light, and the combination of these technologies, are specifically discussed. It is hoped that the symmetry breaking at a supramolecular level could provide useful insights into the understanding of natural homochirality and further designing as well as controlling of functional chiral materials.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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.
This review shows how chirality may be used for the design, construction and evolution of higher ordered and complex chiral nanostructures through hierarchical self-assembly.
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