Electron-donating functional groups strengthen ligand-induced chiral imprinting on CsPbBr3 quantum dots.

Chiral perovskite nanoparticles and films are promising for integration in emerging spintronic and optoelectronic technologies, yet few design rules exist to guide the development of chiral material properties. The chemical space of potential building blocks for these nanostructures is vast, and the mechanisms through which organic ligands can impart chirality to the inorganic perovskite lattice are not well understood. In this work, we investigate how the properties of chiral ammonium ligands, the most common organic ligand type used with perovskites, affect the circular dichroism of strongly quantum confined CsPbBr3 nanocrystals. We show that aromatic ammonium ligands with stronger electron-donating groups lead to higher-intensity circular dichroism associated with the lowest-energy excitonic transition of the perovskite nanocrystal. We argue that this behavior is best explained by a modulation of the exciton wavefunction overlap between the nanocrystal and the organic ligand, as the functional groups on the ligand can shift electron density toward the organic species-perovskite lattice interface to increase the imprinting.

A Facile Approach for the Ligand Free Synthesis of Biocompatible Upconversion Nanophosphors.

Upconversion nanophosphors, particles that can absorb low energy radiation and emit high energy light through multi-photon absorption processes, have gained augmented attention in recent years. Due to their admirable optical and chemical properties, these nanoparticles are finding wide range of applications in the field of bioimaging, light emitting devices and security printing. However, for any practical application, it is extremely important that a facile synthetic route is developed that can lead to the generation of nanophosphors exhibiting efficient upconversion luminescence under diverse experimental conditions. Herein, we report a new ligand-free approach for the synthesis of lanthanide-based upconversion nanoparticles by adopting a simple solid-state synthetic route. The reaction conditions such as temperature and time were optimized to obtain nanophosphors exhibiting enhanced upconversion luminescence. The synthesized nanoparticles, due to its ligand-free nature, could be well dispersed in both aqueous and organic media. The nanophosphors retained the upconversion luminescence under varying time, pH and temperature, indicating that the absence of ligand had least effect on their stability. The nanophosphors were found to exhibit good cell viability even under high concentrations, unveiling their potential as bioimaging agents in the biomedical research.

Mandelic acid appended chiral gels as efficient templates for multicolour circularly polarized luminescence.

Mandelic acid is a medicinally important chiral molecule that is widely used as a vital component in antibiotics, antiseptics and cosmetics. While the medicinal properties of mandelic acid are well known, its aggregation and gelation characteristics, which are crucial to finding applications as cosmetics and ointments, are least explored. We have designed and synthesized a pair of mandelic acid derivatives and investigated their aggregation properties in binary solvent mixtures. The compounds undergo self-assembly through various noncovalent interactions, leading to the formation of robust chiral gels. Strong birefringence could be visualised from the individual structures constituting the gel. The large rod-like chiral structures are utilized as efficient templates for the assembly of ultra-small luminescent achiral carbon nanodots. The transfer of optical activity from the chiral host matrix to the fluorescent guest nanoparticles resulted in the generation of circularly polarized luminescence signals from the hybrid nanocomposites. The use of blue, green and red-emitting nanodots led to the fabrication of multicolour chiral light-emitting materials capable of covering the entire visible range. Considering the numerous medicinal benefits offered by mandelic acid and carbon nanodots, the materials constituting the nanocomposites, the distinct dimensions presented in the current work open new avenues for chiral light emitting materials to be used in biomedical research.