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

Abstract 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 (:PDI 2- ) and their tautomeric spin-zero closed-shell quinoid isomers (PDI 2- ). The self-assembled :PDI 2- /PDI 2- crystal nanobelt alters the spin-dependent excitation evolution, leading to spin-allowed S 0 S 1 → 1 (TT) → T 1 + T 1 singlet fission under visible-light (420 nm~700 nm) and a spin-forbidden S 0 → T 1 transition under near-infrared (700 nm~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.