Optical manipulation with nanoscale chiral fields and related photochemical phenomena

Chiral light-matter interaction occurs when the system consists of the matter and the light has a chiral structure, which is generically called the chiro-optical effect. Circular dichroism and optical rotation are representative spectroscopic methods based on chiro-optical effects. Chiro-optical effects have been widely utilized to detect chiral materials in the system. The chiro-optical effect also has the potential to create chiral materials from achiral materials and chiral optical fields, and to generate chiral optical fields from chiral matter systems. To achieve that, the design and observation of chiral optical field structures are essential. In this article, we describe local chiral optical fields generated in the peripheries of nanomaterials (typically metal nanostructures) irradiated with light. We summarize basic characteristics of nanoscale local chiral optical fields, methods to observe/control the chiral optical field structures at nanomaterials. Then some chemical, optical, and mechanical effects of designed chiral optical fields are described. Chiral nanostructures were created from achiral nanomaterials combined with circularly polarized light. Nucleation of chiral crystals of achiral molecules was achieved by circularly polarized light with the aid of plasmonic materials. Circularly polarized luminescence was observed from achiral fluorescent molecules conjugated with chiral plasmonic nanostructures. On mechanical characteristics, optical forces exerted on chiral materials were found to be dependent on the handedness of incident circularly polarized light, which can be utilized to discriminate the chirality of the material. The concept can be further generalized to the spin-dependent asymmetric light-matter interactions, which will create not only the molecular- and nano-scale chiral structures but also various novel functions of materials that are correlated with the handedness degree of freedom.