NOVELTY - A photocurrent generating system comprises an electron transfer moiety, e.g. fluorescein, tethered to a gold electrode by a conductive spacer moiety e.g. nucleic acid; a biasing potential to be applied to the electrode for reducing the electron transfer moiety to form a reduced electron transfer species that absorbs photon to form an excited electron transfer species. The electron transfer moiety is immersed in an electron transfer solution.    USE - For generating photocurrent (claimed) by forming reduced electron acceptor useful in hydrogen generation, and producing biologically active enzyme cofactor which is useful for converting aldehyde to alcohol, and in reduction of ketones, reductive aminations or reduction of organic acids, and for carrying out various secondary biocatalytic transformations e.g. reductive enzymes or biocatalytic enzyme cascades.    ADVANTAGE - The bias applied to the electrode provides an electron transfer reaction that does not tend to take place on the electrode to form the reduced electron acceptor. In addition, due to the specific rate used for creating reduced electron transfer species, a significant proportion of the electron transfer species exist in reduced form that absorbs photon to form the excited electron transfer species, when appropriate bias is applied to the electrode. The fluorescein has large molar absorptivity to absorb photons, and does not interfere with duplex formation or stability.    DETAILED DESCRIPTION - The system further comprises an electron accepting moiety (e.g. NAD+ or NADP+) in the electron transfer solution, for accepting an electron from the excited electron transfer species to form a reduced electron acceptor (e.g. NADH and NADPH); and an enzyme in the electron transfer solution to utilize the reduced electron acceptor as a cofactor. The enzyme comprises dehydrogenase, alcohol dehydrogenase or reductase. The bias applied to the electrode to form reduced electron transfer species is less than the potential that is required to form the reduced electron acceptor. The rate at which the reduced electron transfer species is created is greater than the rate at which the excited electron transfer species donates the electron to the electron accepting moiety.