Synthesis of Polyviologens As Mediators for Photosystem I-Based Assemblies

Photosystem I (PSI) is a well-studied integral membrane protein that is found in algae, bacteria, and plants that mediates electron photo-excitation. When an electron within PSI is excited by light, it is transported across the protein through a series of electron accepting steps in the electron transport chain and is finally carried to the F_b site, an iron-sulfur complex that acts as a final electron acceptor. This project centers around removing electrons from the F_b site to a counter electrode in order to complete the circuit. Viologens have been an interesting mediator type to study as they have a formal potential very similar to that of the F_b site and thus can accept the electron from PSI with relatively little energy loss. Polyviologens are of specific interest as the polymer network allows increased electron transfer, reduces orientation effects, stabilizing PSI, and allowing a three-dimensional network. Electrochemical tests involving various electrode setups allowed us to generate photo-response data for polyviologens when used in conjunction with PSI. The polyviologens were synthesized using the Menshutkin reaction and characterized with ¹H NMR and electrochemistry. Two different PSI-polymer electrode setups were assembled in order to test the photo-response: a gold macro-electrode system that was alternately layered with a polymer and PSI; and a heavily-P-doped silicon electrode system that used the polymers as aqueous mediators.