Inversion of the Chiroptical Responses of Chiral Gold Nanoparticles with a Gold Film

The deposition of chiral nanoparticles (NPs) onto various substrates is crucial for the fabrication of high-density photonic devices. Understanding the interaction of chiral light and chiral NPs supported on substrates is essential for developing optical sensors and modulators. However, the chiroptical responses of plasmonic chiral NPs on substrates have remained elusive. Here we provide an important understanding of the correlation between the substrate material and the chiroptical response. The scattering dissymmetry factors of individual chiral Au nanocubes are inverted and enhanced with a gold film. Qualitative theories are proposed to analyze the observed variations in the chiroptical signals of chiral NPs on different substrates. Our results offer an encouraging route for modulating and amplifying the chiroptical signals in the use of chiral NPs in light control, light-based quantum technologies, and sensing.

Synthesis of Bitten Gold Nanoparticles with Single-Particle Chiroptical Responses

The introduction of structural complexity to nanoparticles brings them interesting properties. Regularity breaking has been challenging in the chemical synthesis of nanoparticles. Most reported chemical methods for synthesizing irregular nanoparticles are complicated and laborious, largely hindering the exploration of structural irregularity in nanoscience. In this study, the authors have combined seed-mediated growth and Pt(IV)-induced etching to synthesize two types of unprecedented Au nanoparticles, bitten nanospheres and nanodecahedrons, with size control. Each nanoparticle has an irregular cavity on it. They exhibit distinct single-particle chiroptical responses. Perfect Au nanospheres and nanorods without any cavity do not show optical chirality, which demonstrates that the geometrical structure of the bitten opening plays a decisive role in the generation of chiroptical responses.

Design and synthesis of chiral spirobifluorenes

Chiroptical spectroscopic methods serve as a practical tool for the structural characterization of chiral systems based on the interaction with polarized light. The higher sensitivity of these methods, compared with their achiral counterparts, not only enables the determination of absolute configuration and conformational preferences, but also supramolecular interactions may be monitored. In order to expand the applicability of chiroptical systems, the development of functional materials exhibiting intense chiroptical responses is essential. As a proof of principle, we previously constructed chiroptical interfaces via thioacetate-derivatized allenes. Because of the photoisomerization issues associated with allenes, we have recently proposed their replacement by spirobifluorenes to achieve robust chiroptical systems. Thus, we hereby present the design and synthesis of chiral spirobifluorenes bearing thioacetates suitable for suface functionalization.

Chiroptical Symmetry Analysis: Exciton Chirality-Based Formulae to Understand the Chiroptical Responses of Cn and Dn Symmetric Systems

The high sensitivity of chiroptical responses to conformational changes and supramolecular interactions has prompted an increasing interest in the development of chiroptical applications. However, prediction of and understanding the chiroptical responses of the necessary large systems may not be affordable for calculations at high levels of theory. In order to facilitate the development of chiroptical applications, methodologies capable of evaluating the chiroptical responses of large systems are necessary. The exciton chirality method has been extensively used for the interaction between two independent chromophores through the Davydov model. For systems presenting C₂ or D₂ symmetry, one can get the same results by applying the selection rules. In the present article, the analysis of the selection rules for systems with symmetries C_n and D_n with n = 3 and 4 is used to uncover the origin of their chiroptical responses. We foresee that the use of the Chiroptical Symmetry Analysis (CSA) for systems presenting the symmetries explored herein, as well as for systems presenting higher symmetries will serve as a useful tool for the development of chiroptical applications.