Enhancing Oxygenic Photosynthesis by Cross-Linked Perylenebisimide Quantasomes

As the natural-born photoelectrolyzer for oxygen delivery, photosystem II (PSII) is hardly replicated with man-made constructs. However, building on the quantasome hypothesis (Science 1964, 144, 1009-1011), PSII mimicry can be pared down to essentials by shaping a photocatalytic ensemble (from the Greek term soma = body) where visible-light quanta trigger water oxidation. PSII-inspired quantasomes (QS) readily self-assemble into hierarchical photosynthetic nanostacks, made of bis-cationic perylenebisimides (PBI2+) as chromophores and deca-anionic tetraruthenate polyoxometalates (Ru4POM) as water oxidation catalysts (Nat. Chem. 2019, 11, 146-153). A combined supramolecular and click-chemistry strategy is used herein to interlock the PBI-QS with tetraethylene glycol (TEG) cross-linkers, yielding QS-TEG(lock) with increased water solvation, controlled growth, and up to a 340% enhancement of the oxygenic photocurrent compared to the first generation QS, as probed on 3D-inverse opal indium tin oxide electrodes at 8.5 sun irradiance (lambda > 450 nm, 1.28 V vs RHE applied bias, TOFmax = 0.096 +/- 0.005 s(-1), FEO2 > 95%). Action spectra, catalyst mass-activity, light-management, photoelectrochemical impedance spectroscopy (PEIS) together with Raman mapping of TEG-templated hydration shells point to a key role of the cross-linked PBI/Ru4POM nanoarrays, where the interplay of hydrophilic/hydrophobic domains is reminiscent of PSII-rich natural thylakoids.

Automated summary

As a natural photoelectrolyzer for oxygen delivery, PSII is difficult to replicate with man-made constructs. However, by using the quantasome hypothesis, PSII mimicry can be simplified to a photocatalytic ensemble called QS, which can trigger water oxidation using visible-light quanta. In this study, PSII-inspired QS are self-assembled into hierarchical photosynthetic nanostacks, consisting of bis-cationic perylenebisimides as chromophores and deca-anionic tetraruthenate polyoxometalates as water oxidation catalysts. The QS are interlocked with TEG cross-linkers using a supramolecular and click-chemistry strategy, resulting in QS-TEG(lock) with enhanced water solvation, controlled growth, and significantly increased oxygenic photocurrent compared to the first generation QS.