Unveiling Chirality in MoS₂ Nanosheets: A Breakthrough in Phase Engineering for Enhanced Chiroptical Properties

The development of new synthetic strategies to introduce and control chirality in inorganic nanostructures has been highly stimulated by the broad spectrum of potential applications of these exiting nanomaterials. Molybdenum disulfide is among the most investigated transition metal dichalcogenides due to its promising properties for applications that spread from optoelectronic to spintronic. Herein, we report a new two-step approach for the production of chiroptically active semiconductor 2H MoS₂ nanosheets with chiral morphology based on the manipulation of their crystallographic structure. In the first step, metastable metallic 1T MoS₂ nanosheets with chiral morphology were produced via hydrothermal synthesis. Then, thermal annealing was used to progressively tune the conversion of the metallic 1T phase into the thermodynamically stable semiconductor 2H phase while preserving the nanocrystals' chiral morphology. Our detailed study covers the evolution of the chiroptical properties of the material during the crystallographic phase transition, revealing critical insights into the formation of chiroptically active excitonic transitions. This study represents a unique approach to the production of high-quality chiral nanomaterials by exploiting phase engineering, and paves the way for the development of new synthetic methods to further expand the range and properties of chiral nanomaterials.