Chemistry of Singlet Oxygen with a Cadmium–Sulfur Cluster: Physical Quenching versus Photooxidation
2018
Cagan, David A. | Garcia, Arman C. | Li, Kin | Ashen-Garry, David | Tadle, Abegail C. | Zhang, Dong | Nelms, Katherine J. | Liu, Yangyang | Shallenberger, Jeffrey R. | Stapleton, Joshua J. | Selke, Matthias
We investigated the chemistry of singlet oxygen with a cadmium–sulfur cluster, (Me₄N)₂[Cd₄(SPh)₁₀]. This cluster was used as a model for cadmium–sulfur nanoparticles. Such nanoparticles are often used in conjunction with photosensitizers (for singlet oxygen generation or dye-sensitized solar cells), and hence, it is important to determine if cadmium–sulfur moieties physically quench and/or chemically react with singlet oxygen. We found that (Me₄N)₂[Cd₄(SPh)₁₀] is indeed a very strong quencher of singlet oxygen with total rate constants for ¹O₂ removal of (5.8 ± 1.3) × 10⁸ M–¹ s–¹ in acetonitrile and (1.2 ± 0.5) × 10⁸ M–¹ s–¹ in CD₃OD. Physical quenching predominates, but chemical reaction leading to decomposition of the cluster and formation of sulfinate is also significant, with a rate constant of (4.1 ± 0.6) × 10⁶ M–¹ s–¹ in methanol. Commercially available cadmium–sulfur quantum dots (“lumidots”) show similar singlet oxygen quenching rate constants, based on the molar concentration of the quantum dots.
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