Light-Induced Electron Transport Across Semiconductor Electrode/Reaction-Center Film/Electrolyte Interfaces

Abstract— Reaction center (RC) complexes isolated from the photosynthetic bacterium Rhodopseudomonas sphaeroides R‐26 were dried as a film onto platinum and semiconductor (SnO₂) electrodes. The light‐induced primary charge separation which occurs across the biological complex couples electrically with the SnO₂ but not with the metal electrode on the time scale of observation. As the working electrode in a two‐electrode photoelectrochemical cell, RC‐coated SnO₂ generated photovoltages as high as 80 mV and photocurrents as high as 0.5µA·cm² when exposed to light of λ >600nm. The number of quinone molecules per RC strongly influences the photovoltage and photocurrent observed. Photo‐effects generated by RC electrodes persist after several days of storage; however, the kinetics and polarity of the effects are subject to change. The potential use of RC electrodes lies more as a new probe of photosynthetic electron transport rather than as a solar energy conversion device because modification to the RCs and their environment affect the electrical properties of the cell. An energy‐level model is proposed to explain how the photoelectrochemical cell functions.