[Ru(bpy)2dppz]2+ and [Ru(phen)2dppz]2+ as the light switches of the deoxyribose nucleic acid (DNA) molecule have attracted much attention and have become a powerful tool for exploring the structure of the DNA helix. Their interactions have been intensively studied because of the excellent photophysical and photochemical properties of ruthenium compounds. In this perspective, this review describes the recent developments in the interactions of these two classic intercalated compounds with a DNA helix. The mechanism of the molecular light switch effect and the selectivity of these two compounds to different forms of a DNA helix has been discussed. In addition, the specific binding modes between them have been discussed in detail, for a better understanding the mechanism of the light switch and the luminescence difference. Finally, recent studies of single molecule force spectroscopy have also been included so as to precisely interpret the kinetics, equilibrium constants, and the energy landscape during the process of the dynamic assembly of ligands into a single DNA helix.