This study, DOI: 10.1021/ic50114a035, says that the [Ta6Br12]2+cluster is in the most reduced form. But can a photoelectron with enough energy could reduce the cluster...right?
The most truly pathway for this cluster in aqueous medium (such as in protein staining) actually will be not reduction but oxidation, please, see Inorganic Chemistry 1984, 23 (10), S. 1360-1363.