Six Ru(II)bis(tpy) (tpy=2,2′:6′,2″-terpyridine) complexes, functionalized with one or two 2-naphthyl, 1-pyrenyl, or 9-anthracenyl at 4′-position of terpyridine respectively, were investigated with emphasis on their 1 O 2 generation quantum yields and photocleavage capabilities on DNA. For naphthyl and pyrenyl modified complexes, the lowest energy excited state is 3 MLCT, and therefore they behave very similarly to the parent complex, [Ru(tpy) 2 ] 2+ , having very low 1 O 2 generation quantum yields. In contrast, for anthracenyl modified complexes, the lowest energy excited state is anthracene-localized 3 ππ * state, as a result, they exhibit extremely high 1 O 2 generation quantum yields (0.96 and 0.71 for bis- and mono-substituted complexes, respectively) and potent photodamage abilities on calf thymus DNA, suggesting their promising applications in 1 O 2 -involved processes, such as DNA photocleavage.