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

Direct solar-to-hydrogen (STH) 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 S1 excited state for water-splitting based on the common Kasha-allowed S0→S1 excitation; (ii) the H+→H2 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)→T1 + T1 singlet fission under visible-light (420 nm ~ 700 nm) and a spin-forbidden S0→T1 transition under NIR (700 nm ~ 1100 nm) within spin-hybrid chromophores. With a triplet-triplet annihilation upconversion, a newly formed S1 excited state on the diradical-quinoid hybrid induces the H+ reduction through a favorable hydrophilic diradical-mediated electron transfer, which enables simultaneous H2 and O2 production from pure water with an average apparent quantum yield over 1.5% under the visible-to-NIR solar spectrum.