Chirality is one of the most fascinating occurrences in the natural world and plays a crucial role in chemistry, biochemistry, pharmacology, and medicine. Chirality has also been envisaged to play an important role in nanotechnology and particularly in nanophotonics, therefore, chiral and chiroptical active nanoparticles (NPs) have attracted a lot of interest over recent years. Optical activity can be induced in NPs in several different ways, including via the direct interaction of achiral NPs with a chiral molecule. This results in circular dichroism (CD) in the region of the intrinsic absorption of the NPs. This interaction in turn affects the optical properties of the chiral molecule. Recently, studies of induced chirality in quantum dots (QDs) has deserved special attention and this phenomenon has been explored in detail in a number of important papers. In this article, we review these important recent advances in the preparation and formation of chiral molecule–QD systems and analyze the mechanisms of induced chirality, the factors influencing CD spectra shape and the intensity of the CD, as well as the effect of QDs on chiral molecules. We also consider potential applications of these types of chiroptical QDs including sensing, bioimaging, enantioselective synthesis, circularly polarized light emitters, and spintronic devices. Finally, we highlight the problems and possibilities that can arise in research areas concerning the interaction of QDs with chiral molecules and that a mutual influence approach must be taken into account particularly in areas, such as photonics, cell imaging, pharmacology, nanomedicine and nanotoxicology.
Carbon dots (CDs) are light-emitting nanoparticles that show great promise for applications in biology and medicine due to the ease of fabrication, biocompatibility, and attractive optical properties. Optical chirality, on the other hand, is an intrinsic feature inherent in many objects in nature, and it can play an important role in the formation of artificial complexes based on CDs that are implemented for enantiomer recognition, site-specific bonding, etc. We employed a one-step hydrothermal synthesis to produce chiral CDs from the commonly used precursors citric acid and ethylenediamine together with a set of different chiral precursors, namely, L-isomers of cysteine, glutathione, phenylglycine, and tryptophan. The resulting CDs consisted of O,N-doped (and also S-doped, in some cases) carbonized cores with surfaces rich in amide and hydroxyl groups; they exhibited high photoluminescence quantum yields reaching 57%, chiral optical signals in the UV and visible spectral regions, and two-photon absorption. Chiral signals of CDs were rather complex and originated from a combination of the chiral precursors attached to the CD surface, hybridization of lower-energy levels of chiral chromophores formed within CDs, and intrinsic chirality of the CD cores. Using DFT analysis, we showed how incorporation of the chiral precursors at the optical centers induced a strong response in their circular dichroism spectra. The optical characteristics of these CDs, which can easily be dispersed in solvents of different polarities, remained stable during pH changes in the environment and after UV exposure for more than 400 min, which opens a wide range of bio-applications.
Research on materials with perovskite crystal symmetry for photonics applications represent a rapidly growing area of the photonics development due to their unique optical and electrical properties. Among them are high charge carrier mobility, high photoluminescence quantum yield, and high extinction coefficients, which can be tuned through all visible range by a controllable change in chemical composition. To date, most of such materials contain lead atoms, which is one of the obstacles for their large-scale implementation. This disadvantage can be overcome via the substitution of lead with less toxic chemical elements, such as Sn, Bi, Yb, etc., and their mixtures. Herein, we summarized the scientific works from 2016 related to the lead-free perovskite materials with stress on the lasing and lighting applications. The synthetic approaches, chemical composition, and morphology of materials, together with the optimal device configurations depending on the material parameters are summarized with a focus on future challenges.
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