Solar overall water-splitting by a spin-hybrid all-organic semiconductor.

Direct solar-to-hydrogen conversion from pure water using all-organic heterogeneous catalysts remains elusive. The challenges are twofold: (i) full-band low-frequent photons in the solar spectrum cannot be harnessed into a unified S excited state for water-splitting based on the common Kasha-allowed S → S excitation; (ii) the H → H evolution suffers the high overpotential on pristine organic surfaces. Here, we report an organic molecular crystal nanobelt through the self-assembly of spin-one open-shell perylene diimide diradical anions (:PDI) and their tautomeric spin-zero closed-shell quinoid isomers (PDI). The self-assembled :PDI/PDI crystal nanobelt alters the spin-dependent excitation evolution, leading to spin-allowed SS → (TT) → T + T singlet fission under visible-light (420 nm700 nm) and a spin-forbidden S → T transition under near-infrared (700 nm1100 nm) within spin-hybrid chromophores. With a triplet-triplet annihilation upconversion, a newly formed S excited state on the diradical-quinoid hybrid induces the H reduction through a favorable hydrophilic diradical-mediated electron transfer, which enables simultaneous H and O production from pure water with an average apparent quantum yield over 1.5% under the visible to near-infrared solar spectrum.