Three iridium photosensitizers, [Ir(dCF 3 ppy) 2 (N−N)] + , where N−N is 1,4,5,8-tetraazaphenanthrene (TAP), pyrazino[2,3-a]phenazine (pzph), or benzo[a]pyrazino[2,3-h]phenazine (bpph) and dCF 3 ppy is 2-(3,5-bis(trifluoromethylphenyl)pyridine), were found to be remarkably strong photo-oxidants with enhanced light absorption in the visible region. In particular, judicious ligand design provided access to Ir-bpph, with a molar absorption coefficient, ε = 9800 M −1 cm −1 , at 450 nm and an excited-state reduction potential, E(Ir + * /0 ) = 1.76 V vs NHE. These complexes were successful in performing light-driven charge separation and energy storage, where all complexes photo-oxidized seven different electron donors with rate constants (0.089−3.06) × 10 10 M −1 s −1 . A Marcus analysis provided a total reorganization energy of 0.7 ± 0.1 eV for excited-state electron transfer.

The design and characterization of new ruthenium(II) complexes aimed at targeting G‐quadruplex DNA is reported. Importantly, these complexes are based on oxidizing 1,4,5,8‐tetraazaphenanthrene (TAP) ancillary ligands known to favour photo‐induced electron transfer (PET) with DNA. The photochemistry of complexes 1–4 has been studied by classical methods, which revealed two of them to be capable of photo‐abstracting an electron from guanine. From studies of the interactions with DNA through luminescence, circular dichroism, bio‐layer interferometry, and surface plasmon resonance experiments, we have demonstrated the selectivity of these complexes for telomeric G‐quadruplex DNA over duplex DNA. Preliminary biological studies of these complexes have been performed: two of them showed remarkable photo‐cytotoxicity towards telomerase‐negative U2OS osteosarcoma cells, whereas very low mortality was observed in the dark at the same photo‐drug concentration.

Telomeric regions containing G-quadruplex (G4) structures play a pivotal role in the development of cancers. The development of specific binders for G4s is thus of great interest in order to gain a deeper understanding of the role of these structures, and to ultimately develop new anticancer drug candidates. For several years, Ru complexes have been studied as efficient probes for DNA. Interest in these complexes stems mainly from the tunability of their structures and properties, and the possibility of using light excitation as a tool to probe their environment or to selectively trigger their reaction with a biological target. Herein, we report on the synthesis and thorough study of new Ru complexes based on a novel dipyrazino[2,3-a:2',3'-h]phenazine ligand (dph), obtained through a Chichibabin-like reaction. Luminescence experiments, surface plasmon resonance (SPR), and computational studies have demonstrated that these complexes behave as selective probes for G-quadruplex structures.

Photosensitizers that gather high photo‐oxidizing power and strong visible‐light absorption are of great interest in the development of new photo‐chemotherapeutics. Indeed, such compounds constitute attractive candidates for the design of type I photosensitizers that are not dependent on the presence of oxygen. In this paper, we report on the synthesis and studies of new ruthenium(II) complexes that display strong visible‐light absorption and can oxidize guanine residues under visible‐light irradiation, as evidenced by nanosecond transient absorption spectroscopy. The reported compounds also tightly bind to G‐quadruplex DNA structures from the human telomeric sequence (TTAGGG repeat). The kinetic and thermodynamic parameters of the interaction of these Ru(II) complexes with G‐quadruplex and duplex DNA were studied thanks to luminescence titrations and bio‐layer interferometry measurements, which revealed higher affinities towards the non‐canonical G‐quadruplex architecture. Docking experiments and non‐covalent ionic analysis allowed us to gain information on the mode and the strength of the interaction of the compounds towards G‐quadruplex and duplex DNA. The different studies emphasize the substantial influence of the position and the number of non‐chelating nitrogen atoms on the interaction with both types of DNA secondary structures.

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