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-1 excited state for water-splitting based on the common Kasha-allowed S-0 -> S-1 excitation; (ii) the H+ -> H-2 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 (:PDI2-) and their tautomeric spin-zero closed-shell quinoid isomers (PDI2-). The self-assembled :PDI2-/PDI2- crystal nanobelt alters the spin-dependent excitation evolution, leading to spin-allowed S0S1 -> (1)(TT) -> T-1 + T-1 singlet fission under visible-light (420 nm similar to 700 nm) and a spin-forbidden S-0 -> T-1 transition under near-infrared (700 nm similar to 1100 nm) within spin-hybrid chromophores. With a triplet-triplet annihilation upconversion, a newly formed S-1 excited state on the diradical-quinoid hybrid induces the H+ reduction through a favorable hydrophilic diradical-mediated electron transfer, which enables simultaneous H-2 and O-2 production from pure water with an average apparent quantum yield over 1.5% under the visible to near-infrared solar spectrum.