Up- and Down-Shifting Nanomaterials with Chiroptical Responses: Origin of their Chiroptical Activity and Applications

Artificial chiral nanoparticles exhibit unique optical and (photo)physical properties. They can be all-inorganic or organic-inorganic materials that are usually confined to the nanoscale by anchoring organic ligands to their surface. The ligands can also possess distinctive optical and/or (photo)physical properties, thereby adding functionality to the whole nanosystem and constituting an organic-inorganic nanohybrid. Development of luminescent chiral nanoparticles and nanohybrids is pertinent to many applications, such as (bio)sensing, therapeutics, photocatalysis, and optoelectronics, among others. This review deals with different photoactive nanomaterials, displaying either up-shifting emission (nanoparticles consisting of a photoactive or inert matrix doped with lanthanides, Ln(3+), upconversion nanoparticles, UCNPs) or down-shifting emission, such as coinage metal nanoclusters (e.g., gold nanoclusters, AuNCs) and lead halide perovskite nanoparticles (HP NPs), as well as very low emissive nanoparticles, such as plasmonic nanoparticles (such as gold nanoparticles, AuNPs). Special attention is paid to the origin of the chiroptical response of these materials, showing that it is varied and can be alike for some of them.