Highly selective generation of singlet oxygen from dioxygen with atomically dispersed catalysts

Singlet oxygen (¹O₂) as an excited electronic state of O₂ plays a significant role in ubiquitous oxidative processes from enzymatic oxidative metabolism to industrial catalytic oxidation. Generally, ¹O₂ can be produced through thermal reactions or the photosensitization process; however, highly selective generation of ¹O₂ from O₂ without photosensitization has never been reported. Here, we find that single-atom catalysts (SACs) with atomically dispersed MN₄ sites on hollow N-doped carbon (M₁/HNC SACs, M = Fe, Co, Cu, Ni) can selectively activate O₂ into ¹O₂ without photosensitization, of which the Fe₁/HNC SAC shows an ultrahigh single-site kinetic value of 3.30 × 10¹⁰ min^-1 mol^-1, representing top-level catalytic activity among known catalysts. Theoretical calculations suggest that different charge transfer from MN₄ sites to chemisorbed O₂ leads to the spin-flip process and spin reduction of O₂ with different degrees. The superior capacity for highly selective ¹O₂ generation enables the Fe₁/HNC SAC as an efficient non-radiative therapeutic agent for in vivo inhibition of tumor cell proliferation.