Abstract
Developing effective and versatile photocatalytic systems is of great potential in solar energy conversion. Here we investigate the formation of supramolecular catalysts by electrostatic self-assembly in aqueous solution: Combining positively charged porphyrins with negatively charged polyelectrolytes leads to nanoscale assemblies where, next to electrostatic interactions, π–π interactions also play an important role. Porphyrin diacid-polyelectrolyte assemblies exhibit a substantially enhanced catalytic activity for the light-driven oxidation of iodide. Aggregates with the hexavalent cationic porphyrin diacids show up to 22 times higher catalytic activity than the corresponding aggregates under neutral conditions. The catalytic activity can be increased by increasing the valency of the porphyrin and by choice of the loading ratio. The structural investigation of the supramolecular catalysts took place via atomic force microscopy and small angle neutron scattering. Hence, a new facile concept for the design of efficient and tunable self-assembled photocatalysts is presented.
Highlights
Many functional structures in nature are based on non-covalent self-assembly principles
Under strong acidic conditions the two inner nitrogen bases of a metal-free porphyrin ring become protonated leading to a hexavalent species in the case of cationic tetraphenylporphyrins accompanied by a strong colour change from red to green [83]
We have shown that electrostatic self-assembly of highly charged porphrins with polyelectrolytes in aqueous solution can yield a variety of nanostructures with significantly improved properties for photocatalysis
Summary
Many functional structures in nature are based on non-covalent self-assembly principles. Self-assembly has emerged as a powerful method to create supramolecular structures of various sizes, shapes, architectures and functionalities [1,2,3,4,5,6,7,8,9,10,11,12]. Due to their size scale and versatile chemistry, polymers are very suitable building blocks to form a variety of stable assemblies in solution. It is highly interesting to exploit this concept of polyelectrolyte-organic counterion assembly to promote electrostatic self-assembly for the formation of functional nanoassemblies in solution
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