Chirality induction to achiral molecules by silica-coated chiral molecular assemblies

Porphyrin-Based Hybrid Nanohelices: Cooperative Effect between Molecular and Supramolecular Chirality on Amplified Optical Activity

The development of chiral receptors for discriminating the configuration of the analyte of interest is increasingly urgent in view of monitoring pollution in water and waste liquids. Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and Here, we investigate an easy protocol to immobilize the desired non-water-soluble receptors inside a water-dispersible chiral nanoplatform made of silica. This approach induces chirality in the receptors and makes the dye@nanohelix system disperse in a suspension of water without aggregation. We noted strong induction and amplification of chiroptical activity in both achiral and chiral (proline-based or hemicucurbituril-based) porphyrin derivatives with and without zinc ions once confined and organized in nanometer silica helices. The results clearly demonstrated that the organization-induced chirality amplification of porphyrins dominates the molecular chirality, and the amplification is more efficient for more flexible porphyrins (especially free-base and achiral).

Delayed luminescence guided enhanced circularly polarized emission in atomically precise copper nanoclusters

Metal nanoclusters, owing to their intriguing optical properties, have captivated research interest over the years. Of special interest have been chiral nanoclusters that display optical activity in the visible region of the electromagnetic spectrum. While the ground state chiral properties of metal nanoclusters have been reasonably well studied, of late research focus has shifted attention to their excited state chiral investigations. Herein, we report the synthesis and chiral investigations of a pair of enantiomerically pure copper nanoclusters that exhibit intense optical activity, both in their ground and excited states. The synthesis of nanoclusters using l- and d-isomers of the chiral ligand led to the formation of metal clusters that displayed mirror image circular dichroism and circularly polarized luminescence signals. Structural validation using single crystal XRD, powder XRD and XPS in conjunction with chiroptical and computational analysis helped to develop a structure-property correlation that is unique to such clusters. Investigations on the mechanism of photoluminescence revealed that the system exhibits long excited state lifetimes. A combination of delayed luminescence and chirality resulted in circularly polarized delayed luminescence, a phenomenon that is rather uncommon to the field of metal clusters. The chiral emissive properties could be successfully demonstrated in free-standing polymeric films highlighting their potential for use in the field of data encryption, security tags and polarized light emitting devices. Moreover, the fundamental understanding of the mechanism of excited state chirality in copper clusters opens avenues for the exploration of similar effects in a variety of other clusters.

Cooperative interaction between organic and inorganic moieties in hybrid silica nanohelices for enantioselective interaction

Hybrid nanometric helical structures formed by the molecular assemblies of dicationic gemini surfactants with tartrate counterions covered with helical silica walls interact differently with matching or mismatching enantiomers of the tartrate. The difference of the interaction is based on the cooperativity between the chiral crystalline gemini surfactant molecular organization/conformation and the rigid chiral nanospace formed by the helical silica wall.

Induced and Inversed Circularly Polarized Luminescence of Achiral Thioflavin T Assembled on Peptide Fibril

Chiroptical inversion of amyloid fibrils is a novel phenomenon and is of fundamental importance; however, the underlying structural basis remains poorly understood. Here, the co-assembly of Thioflavin T (ThT) with T1 amyloid fibril and the induced supramolecular chirality is investigated by induced circular dichroism (ICD) and circularly polarized luminescence (CPL), followed by direct morphological helicity observation of the fibril by an atomic force microscope (AFM). ThT exhibits negative ICD and CPL when assembled on the left-handed T1 fibril. Interestingly, when ThT dynamically interacts with the T1 fibril, the left-handed fibril partially converts into right-handed, accompanied with the inversion of CD and CPL signals. These results indicate that the morphological helicity of template fibril cannot be arbitrarily distinguished by the sign of chiroptical spectra of the dye/peptide assemblies.