Functionalized vesicles for photocatalytic hydrogen production in water have been prepared by co-embedding of amphiphilic photosensitizers and a hydrogen-evolving catalyst in phospholipid membranes. The self-assembly allows a simple two-dimensional arrangement of the multicomponent system with close spatial proximity, which gave turnover numbers up to 165 for the incorporated amphiphilic cobaloxime water reduction catalyst 3 b under optimized conditions in purely aqueous solution. Superior photocatalytic activity in fluid membranes indicates that mobility and dynamic reorganization of catalytic subunits in the membrane promote the visible-light-driven hydrogen production. The functionalized membranes represent nanostructured assemblies for hydrogen production in aqueous solution mimicking natural photosynthesis.

Artificial photosynthesis is one of the big scientific challenges of today. Self-assembled dynamic interfaces, such as vesicles or micelles, have been used as microreactors to mimic biological photosynthesis. These aggregates can help to overcome typical problems of homogeneous photocatalytic water splitting. Microheterogeneous environments organize catalyst-photosensitizer assemblies at the interface in close proximity and thus enhance intermolecular interactions. Thereby vesicles and micelles may promote photoinitiated charge separation and suppress back electron transfer. The dynamic self-assembled interfaces solubilize non-polar compounds and protect sensitive catalytic units and intermediates against degradation. In addition, vesicles provide compartmentation that was used to separate different redox environments needed for an overall water splitting system. This Minireview provides an overview of the applications of micellar and vesicular microheterogeneous systems for solar energy conversion by photosensitized water oxidation and hydrogen generation.

Self‐assembled vesicles with membrane‐embedded or adsorbed ruthenium polypyridine complexes were further functionalized by the adsorption of an [FeFe]‐hydrogenase subunit mimic to the membrane interface enhancing the photocatalytic hydrogen production in water under acidic conditions. The resulting two‐dimensional membrane assembly places the photosensitizer and hydrogen‐evolving diiron complex in close proximity resulting in a six‐ to twelvefold increase in the turnover number as compared to the same system in the absence of lipid membranes. The interface assembly then enables the combining of hydrophilic and hydrophobic catalytic entities for light‐driven proton reduction in acidic water and provides a flexible method for membrane functionalization.

A photocatalytic hybrid system for the production of hydrogen in purely aqueous solution was prepared by the co‐embedding of hydrophobic oleic acid capped CdSe quantum dots (QD) for light harvesting and an amphiphilic [FeFe]‐hydrogenase subunit mimic for proton reduction into phospholipid vesicle membranes. These bio‐inspired functionalized vesicles concentrate the catalytic subunits in close proximity and show light‐driven hydrogen generation in the presence of ascorbic acid resulting in 651 and 2.47 x 105 catalytic turnovers for the membrane‐incorporated catalyst and the QDs, respectively.

Artificial Photosynthesis at Dynamic Self-Assembled Interfaces in Water -[applications of micellar and vesicular microheterogeneous systems for solar energy conversion by photosensitized water oxidation and hydrogen generation; 44 refs.]. -(HANSEN, M.; TROPPMANN, S.; KOENIG* BURKHARD; Chem. -Eur. J. 22 (2016) 1, 58-72, http://dx.doi.org/10.1002/chem.201503712 ; Inst. Org. Chem., Univ. Regensburg, D-93053 Regensburg, Germany; Eng.) -Schramke 11-270