Optical Properties of Chiral Cobalt Oxide Nanoparticles

Chiral transition metal oxides (TMOs) have garnered significant attention in biological and optoelectronic applications due to their light–matter interaction mechanisms and tunable optical activities. However, the current understanding of their optical properties remains incomplete, limiting further development of related applications. To address this knowledge gap, this work has systematically investigated the photophysical characteristics of chiral TMOs, using chiral cobalt oxide nanoparticles (l/d-Cys-CoO1.35 NPs) as a model system. Transient absorption spectroscopy reveals complex charge-transfer behaviors in the visible wavelength region including ligand-to-metal charge transfer and d–d transitions. Using Z-scan measurements, two- and three-photon absorption cross sections of l/d-Cys-CoO1.35 NPs are determined. Furthermore, the reactive oxygen species assay confirms the synergistic capabilities of Type I (radical-mediated) and Type II (1O2-mediated) photodynamic therapy in these l/d-Cys-CoO1.35 NPs. This work not only advances the fundamental understanding of photophysical properties of chiral TMOs but also provides perspectives for their biomedical applications.