Ruthenium photoreduction methods are described to study electron transfer from cytochrome c to cytochrome c oxidase and within cytochrome oxidase. Methods are described to prepare a ruthenium cytochrome c derivative Ru‐39‐Cc, by labeling the single sulfhydryl group on horse K39C with (4‐bromomethyl‐4′methylbipyridine) (bis‐bipyridine)ruthenium(II).