Optical Activity and Excitonic Characteristics of Chiral CdSe Quantum Dots.

Abstract

Introduction of chirality to colloidal semiconductor quantum dots (QDs) triggers a chiroptical effect. However, there remains a knowledge gap in the mechanism of chirality transfer and amplification from molecules to QDs. By time-dependent density functional theory calculations combined with a correlated electron-hole picture, we explored the chiroptical activity of CdSe QDs decorated with different chiral monocarboxylic acids from an excitonic perspective. Our calculations showed strong circular dichroism (CD) signals in the visible region for the chiral CdSe QDs. The excitonic states with large CD originate from QDs, while the chiral molecules break the orthogonality between electric and magnetic transition dipoles, which synergistically facilitates the prominent dissymmetric effect. The considered monocarboxylic acid chiral molecules all favor the bidentate adsorption configuration of the carboxyl group on the CdSe surface, endowing an identical CD signature but distinct excitonic characteristics. These findings are crucial for the regulation of chirality and excitons in semiconductor QDs to develop excitonic devices.