RuBP-4S ([Ruthenium(bathophenanthroline)(bis(bathophenanthrolinedisulfonate))],disodium salt) is a luminescent ruthenium complex similar to RuBPS. Two of the bathophenanthroline ligands are bis-sulfonated while the third bathophenanthroline ligand is neutral, resulting in an overall double negative charges of the ruthenium complex. RuBP-4Sshares the spectral properties of RuBPS and may also have similar applications.