A facile and automated procedure for the incorporation of a derivatized Ru(bpy)(3)(2+) in an oligodeoxynucleotide is reported. The Ru(bpy)(3)(2+)-thymidine phosphoramidite is synthesized, and then incorporated in DNA using a standard protocol on an automated DNA solid-phase synthesizer. The structure of the DNA duplex is not altered after labeling with Ru(bpy)(3)(2+). Photophysical studies of the novel ruthenium trisdiimine thymidine complex as well as the corresponding labeled oligodeoxynucleotides demonstrate that the favorable properties associated with the ruthenium complex are retained after covalent attachment to the nucleoside and oligodeoxynucleotide.