Initial Quenching Efficiency Determines Light‐Driven H₂ Evolution of [Mo₃S₁₃]²⁻ in Lipid Bilayers

Abstract

Nature uses reactive components embedded in biological membranes to perform light‐driven photosynthesis. Here, we report a model artificial photosynthetic system for light‐driven hydrogen (H2) evolution. The system is based on liposomes where amphiphilic ruthenium trisbipyridine based photosensitizer (RuC9) and the H2 evolution reaction (HER) catalyst [Mo3S13]2‐ are embedded in biomimetic phospholipid membranes. When DMPC was used as the main lipid of these light‐active liposomes, increased catalytic activity (TONCAT ~ 200) was observed compared to purely aqueous conditions. Although all tested lipid matrixes, including DMPC, DOPG, DPPC and DOPG liposomes provided similar liposomal structures according to TEM analysis, only DMPC yielded high H2 amounts. In situ scanning electrochemical microscopy (SECM) measurements using Pd microsensors revealed an induction period of around 26 minutes prior to H2 evolution, indicating an activation mechanism which might be induced by the fluid‐gel phase transition of DMPC at room temperature. Stern Volmer‐type quenching studies revealed that electron transfer dynamics from the excited state photosensitizer are most efficient in the DMPC lipid environment giving insight for design of artificial photosynthetic systems using lipid bilayer membranes.

Factors that Impact Photochemical Cage Escape Yields

“…Functional groups present on the photosensitizer that are competent for hydrogen bonding, π-stacking, and/or a cationic/anionic charge may tune cage escape yields in a rational manner. An avenue that deserves further investigation is the supramolecular assembly of photosensitizers within micelles or liposomes (Figure D). ,,, Such supramolecular assemblies provide unique opportunities for vectoral electron transfer that provides the physical separation of the redox products and, hence, enhanced cage escape. In addition, local charges on the micelles or liposomes prove useful platforms for the study of Coulombic attraction/repulsion on cage escape processes.…”

“…Micelles or lipid bilayer have been chemically engineered to tune the cage escape yields by introduction of ionic charges, micelles, or lipid bilayers that attract or repel redox-active species. ,− In these assemblies, charge separation was modulated and facilitated by preassociation of the photosensitizers and the redox-active quenchers at the micelle interface. After excited-state electron transfer, the cage escape process was impacted by the hydrophobicity and ionic charges of the radical products that differed from those of the ground state.…”