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

Singlet oxygen ( 1 O 2 ) as an excited electronic state of O 2 plays a significant role in ubiquitous oxidative processes from enzymatic oxidative metabolism to industrial catalytic oxidation. Generally, 1 O 2 can be produced through thermal reactions or the photosensitization process; however, highly selective generation of 1 O 2 from O 2 without photosensitization has never been reported. Here, we find that single-atom catalysts (SACs) with atomically dispersed MN 4 sites on hollow N-doped carbon (M 1 /HNC SACs, M = Fe, Co, Cu, Ni) can selectively activate O 2 into 1 O 2 without photosensitization, of which the Fe 1 /HNC SAC shows an ultrahigh single-site kinetic value of 3.30 × 10 10 min -1 mol -1 , representing top-level catalytic activity among known catalysts. Theoretical calculations suggest that different charge transfer from MN 4 sites to chemisorbed O 2 leads to the spin-flip process and spin reduction of O 2 with different degrees. The superior capacity for highly selective 1 O 2 generation enables the Fe 1 /HNC SAC as an efficient non-radiative therapeutic agent for in vivo inhibition of tumor cell proliferation.