Sensitization of Light-Induced Charge Separation in Photosystem I by Synthetic Fluorescent Dyes

An attempt has been made to sensitize the photochemical process within photosystem (PS) I to green light using artificial fluorescent dyes. Rhodamine (Rh) derivatives, which exhibit intense light absorption for green light, were introduced to PS I surfaces as an additional light-harvesting antenna. To mimic the soluble extrinsic light- harvesting antenna such as phycobilisomes in cyanobacteria, XRh was introduced covalently to stroma and lumenal surfaces of PS I through an amide linkage. Further, an amphiphilic polymer bearing Rh6G moieties was complexed with the hydrophobic membrane integral regions of PS I. Under preferential excitation of the Rh derivatives, Rh-modified PS I exhibited a larger absorbance change attributed to the photooxidation of the primary electron donor P700 than that observed in native PS I. These results show that Rh derivatives function as artificial light-harvesting antennae to drive successfully PS I photochemistry by green light.