Fine control on the photochemical and photobiological properties of Ru(ii) arene complexes

Abstract

A series of six Ru(arene) complexes, [(η⁶-p-cymene)Ru(dpb)(py-R)]²⁺ (1–6, dpb = 2,3-bis(2-pyridyl)benzoquinoxaline, py-R = 4-substituted pyridine, R = N(CH₃)₂, NH₂, OCH₃, H, COOCH₃ and NO₂), were synthesized and their photochemical and photobiological properties were compared in detail. The electron push/pull character of the R groups has a significant impact on both ligand photodissociation and ¹O₂ generation of the complexes. The photoinduced DNA covalent binding capabilities increase from 1 to 6 under both aerobic and anaerobic conditions, and DNA photocleavage occurs simultaneously in aerobic environments. 4 has the most potent phototoxicity against human lung carcinoma A549 cells among the examined complexes. The substituent effect may be ascribed to the influences of the R groups on the energy levels of ³MC and ³MLCT states as well as the energy gaps between ³MC, ³MLCT and dpb-based ³IL states. Similar chemical modification on bidentate and arene ligands or other sites of the pyridine ligand may lead to more efficient agents with PDT and/or PACT activities.