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

Singlet oxygen (O-1(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, O-1(2) can be produced through thermal reactions or the photosensitization process; however, highly selective generation of O-1(2) from O-2 without photosensitization has never been reported. Here, we find that single-atom catalysts (SACs) with atomically dispersed MN4 sites on hollow N-doped carbon (M-1/HNC SACs, M = Fe, Co, Cu, Ni) can selectively activate O-2 into O-1(2) without photosensitization, of which the Fe-1/HNC SAC shows an ultrahigh single-site kinetic value of 3.30 x 10(10) min(-1) mol(-1), representing top-level catalytic activity among known catalysts. Theoretical calculations suggest that different charge transfer from MN4 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 O-1(2) generation enables the Fe-1/HNC SAC as an efficient non-radiative therapeutic agent for in vivo inhibition of tumor cell proliferation.