Efficient Generation of Hydrated Electrons for Organic Transformations Using Manganese-Doped Cd-Free Quantum Dots.

Photoemission materials, which can emit free electrons under light illumination, hold substantial technological value in diverse fields ranging from advanced electron sources to photochemistry. Spin-exchange Auger interaction, recently discovered in Mn2+-doped colloidal quantum dots (QDs), suggests the potential of these low-cost materials for efficient photoemission. However, previous Cd-based QDs suffer from an inherent toxicity issue, and they typically require multistep spin-exchange Auger interaction to achieve free electron ejection. Here, we report Mn2+-doped ZnSe QDs as a promising solution to these issues. Besides avoiding toxic materials, ZnSe-based QDs feature a high-energy conduction band that allows for efficient photoemission by absorbing only two photons, as confirmed by our femtosecond transient absorption measurements. The first photon enacts subpicosecond energy transfer from a photoexcited QD to a Mn2+-dopant. The second photogenerated electron-hole pair in the QD subsequently undergoes subpicosecond spin-exchange Auger interaction with the excited dopant, which transfers energy to the QD electron and ejects it into the vacuum. In aqueous solution, this leads to hydrated electrons with quantum efficiency exceeding 7%. Importantly, the millisecond excited-state lifetime of Mn2+-dopants enables efficient photoemission under continuous-wave illumination, which is leveraged to drive a dechlorination reaction of chloroacetate.