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[Display omitted] Since the chiral emission of excited states is observed on carbon dots (CDs), exploration towards the design and synthesis of chiral CDs nanomaterials with circularly polarized luminescence (CPL) properties has been at a brisk pace. In this regard, the "host and guest" co-assembly strategy based on the combination of CDs and chiral templates has been of unique interest recently for its convenient operation, multicolor tunable CPL, and wide application of prepared CDs-composited materials in optoelectronic devices and information encryption. However, the existing chiral templates that match perfectly with chiral CDs exhibiting optical activity both in ground and excited states are rather scarce. In this work, we synthesize the chiral CDs that could induce the spontaneous supramolecular self-assembly of N-(9-fluorenylmethox-ycarbonyl) (Fmoc)-protected glutamic acid to form chiral hydrogels with helical nanostructure. The co-assembled hydrogels show powerful chiral template function, which not only enable chiral CDs with a luminescence dissymmetry factor (g lum) up to 10-2, but also have universal chiral transfer to inserted dye molecules, realizing full-color CPL and Förster resonance energy transfer (FRET) CPL as well as the distinction between left and right circularly polarized light. This CPL-active template based on chiral CDs enriches the design scenario of chiral functionalized nanomaterials. [ABSTRACT FROM AUTHOR]

The synthesis of a family of chiral and enantiomerically pure pyridyl‐diamide (pda) ligands that upon complexation with europium [Eu(CF3SO3)3] result in chiral complexes with metal centered luminescence is reported; the sets of enantiomers giving rise to both circular dichroism (CD) and circularly polarized luminescence (CPL) signatures. The solid‐state structures of these chiral metallosupramolecular systems are determined using X‐ray diffraction showing that the ligand chirality is transferred from solution to the solid state. This optically favorable helical packing arrangement is confirmed by recording the CPL spectra from the crystalline assembly by using steady state and enantioselective differential chiral contrast (EDCC) CPL Laser Scanning Confocal Microscopy (CPL‐LSCM) where the two enantiomers can be clearly distinguished. [ABSTRACT FROM AUTHOR]

Abstract The synthesis of a family of chiral and enantiomerically pure pyridyl‐diamide (pda) ligands that upon complexation with europium [Eu(CF3SO3)3] result in chiral complexes with metal centered luminescence is reported; the sets of enantiomers giving rise to both circular dichroism (CD) and circularly polarized luminescence (CPL) signatures. The solid‐state structures of these chiral metallosupramolecular systems are determined using X‐ray diffraction showing that the ligand chirality is transferred from solution to the solid state. This optically favorable helical packing arrangement is confirmed by recording the CPL spectra from the crystalline assembly by using steady state and enantioselective differential chiral contrast (EDCC) CPL Laser Scanning Confocal Microscopy (CPL‐LSCM) where the two enantiomers can be clearly distinguished.

Light that rotates in a circular spiral when viewed from the front is known as circularly polarized luminescence (CPL), and can be divided into two types, namely, left- and right-rotating light. To emit both left- and right-rotating CPLs, two types of optically active luminophores, namely, enantiomer D- and L-bodies, are generally required. This mini-review mainly discusses our latest study on CPL properties via the control of the pyrene ring as the luminescent unit incorporated into chiral peptides. In this study, optically active peptide–pyrene organoluminescent materials that emit CPL were synthesized by combining a peptide as a frame and two pyrene rings as a luminescent unit. By adjusting the interpyrene distance, external conditions, and absolute chiral configuration (D- or L-configuration), the chiral spatial configuration of the luminescent pyrene ring was precisely controlled. Consequently, the direction of CPL rotation from pyrenylalanine-containing peptides with the same configuration was successfully controlled. [ABSTRACT FROM AUTHOR]

Abstract Understanding the precise molecular arrangement of chiral supramolecular polymers is essential not only to comprehend complex superstructures like proteins and DNA but also for the development of next‐generation optoelectronic materials, including materials displaying high‐performance circularly polarized luminescence (CPL). Herein, we report the first chiral supramolecular polymer systems based on hydrazone–pyridinium conjugates comprising alkyl chains of different lengths, which afforded control of the apparent supramolecular chirality. Although supramolecular chirality is governed basically by the remote chiral centers of alkyl chains, helicity inversion was achieved by controlling the conditions under which the hydrazone building blocks underwent aggregation (i.e., solvent compositions or temperature). More importantly, the addition of water to the system led to aggregation‐induced hydrazone deprotonation, which resulted in a completely different self‐assembly behavior. Structural water molecules played an essential role, forming the assembly's channel‐like backbone, around which hydrazone molecules gathered as a result of hydrogen bonding interactions. Further co‐assembly of an achiral hydrazone luminophore with the given supramolecular polymer system allowed the fabrication of a novel CPL‐active hydrazone‐based material exhibiting a high maximum value for the photoluminescence dissymmetry factor of −2.6 × 10−2.

Chiral molecules are essential for the development of advanced technological applications in spintronic and photonic. The best systems should produce large circularly polarized luminescence (CPL) as estimated by their dissymmetry factor (glum), which can reach the maximum values of −2 ≤ glum ≤ 2 when either pure right- or left-handed polarized light is emitted after standard excitation. For matching this requirement, theoretical considerations indicate that optical transitions with large magnetic and weak electric transition dipole moments represent the holy grail of CPL. Because of their detrimental strong and allowed electric dipole transitions, popular chiral emissive organic molecules display generally moderate dissymmetry factors (10−5 ≤ glum ≤ 10−3). However, recent efforts in this field show that glum can be significantly enhanced when the chiral organic activators are part of chiral supramolecular assemblies or of liquid crystalline materials. At the other extreme, chiral EuIII- and SmIII-based complexes, which possess intra-shell parity-forbidden electric but allowed magnetic dipole transitions, have yielded the largest dissymmetry factor reported so far with glum ~ 1.38. Consequently, 4f-based metal complexes with strong CPL are currently the best candidates for potential technological applications. They however suffer from the need for highly pure samples and from considerable production costs. In this context, chiral earth-abundant and cheap d-block metal complexes benefit from a renewed interest according that their CPL signal can be optimized despite the larger covalency displayed by d-block cations compared with 4f-block analogs. This essay thus aims at providing a minimum overview of the theoretical aspects rationalizing circularly polarized luminescence and their exploitation for the design of chiral emissive metal complexes with strong CPL. Beyond the corroboration that f–f transitions are ideal candidates for generating large dissymmetry factors, a special attention is focused on the recent attempts to use chiral CrIII-based complexes that reach values of glum up to 0.2. This could pave the way for replacing high-cost rare earths with cheap transition metals for CPL applications.

Circularly polarized luminescence (CPL) has attracted significant attention in the fields of chiral photonic science and optoelectronic materials science. In a CPL-emitting system, a chiral luminophore derived from chiral molecules is usually essential. In this review, three non-classical CPL (NC-CPL) systems that do not use enantiomerically pure molecules are reported: (i) supramolecular organic luminophores composed of achiral organic molecules that can emit CPL without the use of any chiral auxiliaries, (ii) achiral or racemic luminophores that can emit magnetic CPL (MCPL) by applying an external magnetic field of 1.6 T, and (iii) circular dichroism-silent organic luminophores that can emit CPL in the photoexcited state as a cryptochiral CPL system.

For the selective emission of positive- and negative-sign circularly polarized luminescence (CPL), two chiral organic luminophores with opposing chirality are generally needed. In this study, the solution-state CPL sign of an axially chiral binaphthylacetic acid organic luminophore was successfully controlled by changing the solvent from chloroform (or methanol) to dimethylformamide (or acetonitrile). [ABSTRACT FROM AUTHOR]

Abstract: It is important to first determine the solid-state chiral optical properties of basic fluorescence supramolecular building blocks that can form a network structure via intermolecular interactions. Although the circularly polarized luminescence (CPL) properties of (R)-1,1′-binaphthyl-2,2′-dicarboxylic acid with axial chirality could not be measured in either the solution or solid states, those of (R)-1,1′-binaphthyl-2,2′-diyl hydrogen phosphate with axial chirality were successfully measured in both states. The solid-state CPL originates from the intramolecular interaction of single molecule, rather than intermolecular interactions in the crystal. [Copyright &y& Elsevier]

Chiral supramolecular gels have been widely reported and applied in asymmetric catalysis, chiral recognition and circularly polarized luminescence (CPL). Guanosine, a biomolecule with both hydrogen bond donors and receptors on their purine rings, can self-assemble to form chiral G-quadruplexes, providing a good template for building CPL materials. Herein, we constructed the quadruplex-based ionogels in the absence of metal ions via dissolving a certain amount of guanosine into an ionic liquid, ethylammonium nitrate (abbreviated as EAN), where the cations of EAN worked as stabilizers of the G-quadruplexes. The introduction of K+ or Sr2+ reduced the guanosine concentration required to form G-quadruplex-based gels in EAN. The Sr2+ was found to disturb the homopolar stacking of G-quartets and triggered the heteropolar stacking, and thereby overturned the chirality of G-quadruplexes. All ionogels were CPL-active without additional luminescent materials, producing the left-handed CPL for K+ and right-handed CPL for Sr2+, respectively. Regulating the proportion of metal ions could modulate the chirality and CPL of the hybrid G-quadruplexes. The chiral-controllable ionogels in this work are easy to prepare and are promising to provide potential applications for constructing polarized light-emitting devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Chiral organic and organometallic luminophores that possess circularly polarized luminescence (CPL) properties in the near-ultraviolet to near-infrared region have several useful applications. However, the CPL properties are subject to inherent factors of the compounds; to date, studies on the CPL properties influenced by amino acids and peptides are scarce. Consequently, we developed peptide-pyrene organic luminophores exhibiting various CPL properties. It is conceivable that the peptide-pyrene organic luminophores can be obtained as aggregates when dissolved in a solution. It is also possible that the formation of aggregates makes it difficult to accurately examine the CPL of the peptide in the solution. This study showed that the introduction of sterically hindered 2-aminoisobutyric acid (Aib) units into the peptide backbone inhibits aggregate formation. The resulting luminophores exhibit CPL properties owing to the presence of pyrene units. The results of this study can form a basis for the design of future materials that use peptide-pyrene organic luminophores. [ABSTRACT FROM AUTHOR]

Circularly polarized luminescence (CPL) has attracted significant attention in the fields of chiral photonic science and optoelectronic materials science. In a CPL-emitting system, a chiral luminophore derived from chiral molecules is usually essential. In this review, three non-classical CPL (NC-CPL) systems that do not use enantiomerically pure molecules are reported: (i) supramolecular organic luminophores composed of achiral organic molecules that can emit CPL without the use of any chiral auxiliaries, (ii) achiral or racemic luminophores that can emit magnetic CPL (MCPL) by applying an external magnetic field of 1.6 T, and (iii) circular dichroism-silent organic luminophores that can emit CPL in the photoexcited state as a cryptochiral CPL system. [ABSTRACT FROM AUTHOR]

• Novel axially chiral oligonaphthyl ligands were successfully synthesized. • Binaphthyl-Eu(III) organometallic luminophores having circularly polarized luminescence (CPL) properties were successfully prepared. • The CPL signs of these Eu(III) luminophores were successfully inverted by inserting bulky units into the binaphthyl backbone. • This work offers a novel approach for controlling the CPL signs of organometallic circularly polarized luminophores. The circularly polarized luminescence (CPL) signs of Eu(III) luminophores coordinated to axially chiral binaphthyl derivatives carrying acetic acid residues [(R,R,R)- 4 were inverted compared to those bearing compounds (R)- 1–3 by inserting bulky naphthalene units into the binaphthyl backbone. The suitable steric difference between the phenyl group and the highly bulky naphthalene group on the binaphthyl backbone causes a chiral coordination change for all ligands on Eu(III). This substituent domino effect on the 1,1,1,5,5,5-hexafluoro-pentane-1,4-dione (hfa) ligands on Eu(III) caused by the bulky naphthyl group on the binaphthyl ligand causes the apparent change of the CPL sign in the photo-excited state, although (R)- 1 – 3 /Eu and (R,R,R)- 4 /Eu exhibited the same circular dichroism sign in the ground state. [ABSTRACT FROM AUTHOR]

Chiral molecules are essential for the development of advanced technological applications in spintronic and photonic. The best systems should produce large circularly polarized luminescence (CPL) as estimated by their dissymmetry factor ( g lum ), which can reach the maximum values of -2 ≤ g lum ≤ 2 when either pure right- or left-handed polarized light is emitted after standard excitation. For matching this requirement, theoretical considerations indicate that optical transitions with large magnetic and weak electric transition dipole moments represent the holy grail of CPL. Because of their detrimental strong and allowed electric dipole transitions, popular chiral emissive organic molecules display generally moderate dissymmetry factors (10 -5 ≤ g lum ≤ 10 -3 ). However, recent efforts in this field show that g lum can be significantly enhanced when the chiral organic activators are part of chiral supramolecular assemblies or of liquid crystalline materials. At the other extreme, chiral Eu III - and Sm III -based complexes, which possess intra-shell parity-forbidden electric but allowed magnetic dipole transitions, have yielded the largest dissymmetry factor reported so far with g lum ~ 1.38. Consequently, 4f-based metal complexes with strong CPL are currently the best candidates for potential technological applications. They however suffer from the need for highly pure samples and from considerable production costs. In this context, chiral earth-abundant and cheap d-block metal complexes benefit from a renewed interest according that their CPL signal can be optimized despite the larger covalency displayed by d-block cations compared with 4f-block analogs. This essay thus aims at providing a minimum overview of the theoretical aspects rationalizing circularly polarized luminescence and their exploitation for the design of chiral emissive metal complexes with strong CPL. Beyond the corroboration that f-f transitions are ideal candidates for generating large dissymmetry factors, a special attention is focused on the recent attempts to use chiral Cr III -based complexes that reach values of g lum up to 0.2. This could pave the way for replacing high-cost rare earths with cheap transition metals for CPL applications., (Copyright © 2020 Doistau, Jiménez and Piguet.)