Mimicking Photosystem I with a Transmembrane Light Harvester and Energy Transfer-Induced Photoreduction in Phospholipid Bilayers

Abstract

Photosystem I (PS I) is a transmembrane protein that assembles perpendicular to the membrane, and performs light harvesting, energy transfer, and electron transfer to a final, water-soluble electron acceptor. We present here a supramolecular model of it formed by a bicationic oligofluorene 12+ bound to the bisanionic photoredox catalyst eosin Y (EY2−) in phospholipid bilayers. According to confocal microscopy, molecular modeling, and time dependent density functional theory calculations, 12+ prefers to align perpendicularly to the lipid bilayer. In presence of EY2−, a strong complex is formed (Ka=2.1±0.1×106 m−1), which upon excitation of 12+ leads to efficient energy transfer to EY2−. Follow-up electron transfer from the excited state of EY2− to the water-soluble electron donor EDTA was shown via UV–Vis absorption spectroscopy. Overall, controlled self-assembly and photochemistry within the membrane provides an unprecedented yet simple synthetic functional mimic of PS I.