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.