In Vitro Solar Conversion after the Primary Light Reaction in Photosynthesis. Reversible Photogalvanic Effects of Chlorophyll-Quinhydrone Half-Cell Reactions

In this publication, we report the observation of photogalvanic effects arising from chlorophyll a-quinhydrone (Q: H₂Q, 1:1) half-cell reactions. Platinum electrodes have been employed. In the presence of light, a photocurrent is developed as Chl a aggregates presumably undergo a charge-transfer interaction that results in the creation of a p-type semiconductor film. The observed photopotential at the Pt-Chl a electrode is positive. When the light is turned off, the half-cells regress toward the preillumination conditions, and a reverse current is observed. The spectral response of the photogalvanic effect has been determined. It has been found that a distribution of Chl a-H₂O aggregates contribute to the observed photocurrent. The in vitro solar conversion results are discussed in terms of the recently proposed primary light reaction model of photosynthesis.