Chiral Transition Metal Oxides: Synthesis, Chiral Origins, and Perspectives

Abstract

to inorganic nanocrystals (NCs) whose unique physicochemical properties could be easily tuned by altering their size, shape, or ingredient, providing a powerful platform for exploring enhanced chiroptical effects, chirogenesis, and potentials in which chiral inorganic NCs could provide to interdisciplinary fields such as optical and biosensing, [2,3] chiral bioimaging, [4] and polarization-based display devices. [5] In general, chirality in inorganic NCs can be obtained from: [6,7] 1) intrinsic chirality formed by chiral crystals, lattice distortions, and defects, [8-10] 2) chiral shape with subwavelength dimensions, [11] 3) chirality transfer via chiral assembled nanostructures of achiral NCs, [5,12] and 4) chiral interactions of achiral NCs with chiral molecules [13] as depicted in Figure 1. The most famous property of chiral nanostructure is the optical activity which refers to the ability of a chiral unit to rotate the plane of plane polarized light. [14] In modern optics, this property is associated to the circular dichroism (CD) phenomenon, which concerns the absorption difference between left and right circularly polarized (LCP and RCP) light, therefore CD-based spectroscopies are generally regarded as powerful tools to detect chirality of a measured sample. With rapid development, a number of cutting-edge work concerning on chiral metal nanoparticles (NPs), chiral semiconductor NCs, chiral ceramics, and metal coordinate systems has been investigated recently. [6] Among them, chiral transition metal oxides (TMOs) are a newly discovered area attracting tremendous attentions because of their striking feature for nonstoichiometry even though great challenges on establishing systematic control over the synthesis and theoretical supports for chirality induction mechanisms still remain. Since the nature of metal-oxygen bonding in TMOs can vary from nearly ionic to covalent or metallic, the physicochemical properties of TMOs are strongly related to their outer d electrons. [15] When combined with chiral molecules, the overlap of the orbital of chiral molecules with the density of states of TMOs or formation of chiral surfaces can bring in tunable chirality for TMOs from UV-visible to near infrared region, endowing fascinating chiroptical properties. Therefore, herein, we emphasize recent progress on chiral TMOs in terms of their synthesis, CD effects, and possible mechanisms of induced optical chirality. In Section 2, theoretical background on the origin of induced chirality in TMOs nanostructures is briefly introduced. Section 3 will show recent progress of chiral TMOs with their synthetic Transition metal oxides (TMOs) consist of a series of solid materials, exhibiting a wide variety of structures with tunability and versatile physicochemical properties. Such a statement is undeniably true for chiral TMOs since the introduction of chirality brings in not only active optical activities but also geometrical anisotropy due to the symmetry-breaking effect. Although progressive investigations have been made for accu...

Circularly polarized luminescence of agglomerate emitters

“…As expected, chiral luminescent molecules with CPL activities have grown enormously over the years. [59][60][61][62] However, aside from liquid crystalline conjugated polymers [63,64] and some self-assemblies from single-source, [60] most of them with small g lum values (10 −5 -10 −2 ) were investigated in the solution. [65][66][67][68][69][70][71] From solution to condensed phase to solid state, the performance of organic materials becomes worse even disappeared due to common aggregation-caused quenching (ACQ) effect.…”

Chirality communications between inorganic and organic compounds

“…Such “indirect transfer” process has also been observed in other material systems, 86,87 such as zeolites and MOFs, 88 silica, 83 CuO, 84 ZnO, 89 TiO 2, 90,91 CaCO 3, 85 and so forth. The common feature of these materials is that almost all of them contain spiral structures.…”

“…The structural evolution process could mimic the biogeneration of chiral objects, in which the structure varied along time and spiral structures gradually expanded. 9 Such "indirect transfer" process has also been observed in other material systems, 86,87 such as zeolites and MOFs, 88 silica, 83 CuO, 84 ZnO, 89 TiO 2, 90,91 CaCO 3, 85 and so forth. The common feature of these materials is that almost all of them contain spiral structures.…”

Shining light on chiral inorganic nanomaterials for biological issues

“…Chiral arrangement of achiral nanoparticles. Adapted with permission from 14 , copyright 2020 Wiley-VCH.…”

“…In sum, based on substrate material's property, chirality actually acts as a role of game changer who often introduces new potentials/properties or enhances the pristine properties/functions of the substrate materials endowing them chances for more and better performances in biological applications, but also new insights for establishing revolutionary strategies for biological issues 11 - 14 . In this review, therefore we focus on current research state and clinical applications of chiral nanomaterials in biological systems with special attentions to chiral metal- or semiconductor-based nanostructures which possess excitonic features.…”