Optical Activity and Excitonic Characteristics of Chiral CdSe Quantum Dots

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.