Targeted Modulation\nof Photocatalytic Hydrogen Evolution\nActivity by Nickel-Substituted Rubredoxin through Functionalized Ruthenium\nPhototriggers

Light-driven\nhydrogen evolution is a promising means of sustainable\nenergy production to meet global energy demand. This study investigates\nthe photocatalytic hydrogen evolution activity of nickel-substituted\nrubredoxin (NiRd), an artificial hydrogenase mimic, covalently attached\nto a ruthenium phototrigger (RuNiRd). By systematically modifying\nthe para-substituents on Ru(II) polypyridyl complexes, we sought to\noptimize the intramolecular electron transfer processes within the\nRuNiRd system. A series of electron-donating and electron-withdrawing\ngroups were introduced to tune the photophysical, photochemical, and\nelectrochemical properties of the ruthenium complexes. Our findings\nreveal that electron-donating substituents can increase the hydrogen\nevolution capabilities of the artificial enzyme to a point; however,\nthe complexes with the most electron-donating substituents suffer\nfrom short lifetimes and inefficient reductive quenching, rendering\nthem inactive. The present work highlights the intricate balance required\nbetween driving force, lifetime, and quenching efficiency for effective\nlight-driven catalysis, providing valuable insights into the design\nof artificial enzyme–photosensitizer constructs.