Two new dinuclear iridium (Ir) complexes bridged by a conjugated aromatic tppz ligand, (bhq)2Ir(tppz)Ir(bhq)2 (1) and (ppy)2Ir(tppz)Ir(ppy)2 (2) (bhq = benzo(h)quinolone, ppy = phenyl-pyridine, tppz = tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine), were prepared. The DNA binding properties of complexes 1 and 2 were studied using single-stranded DNA, double-stranded DNA, and G-quadruplex DNA. G-Quadruplex binding was characterized by higher emission enhancements than those observed with other control DNA strands. Photophysical properties of complexes 1 and 2 indicated that 1 displayed selective G-quadruplex binding affinity, but 2 did not. The emission properties of complexes 1 and 2 were also studied using liposomes in order to understand their possible interactions with lipid-rich organelles in live cells. The phosphorescence intensity of 1 and 2 was enhanced upon interaction with liposomes, but 2 showed greater enhancement. We also confirmed that 1 and 2 could be used as probes in live cells. Complexes 1 and 2 were intensely stained in HeLa cervical cancer cells. Excitation with a λ = 488 nm laser showed red emission localized in the cytosol of cells. Cellular studies showed that 1 and 2 were located inside HeLa cells, but neither complex passed through the nuclear membrane. However, complexes 1 and 2 possessed superior photostability, indicating their role as good luminescent agents for imaging and tracking the endoplasmic reticulum (ER) in live cells. Overall, complex 1 exhibited better selectivity for G-quadruplexes, liposomes, and ER staining.
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation of Korea's (NRF) grant funded by the Korean Government (MEST) (NRF-2016R1A2B4012488). This work was also supported by a grant from the National Creative Research Initiative Programs of the National Research Foundation of Korea (NRF) funded by the Korean Government (MSIP) (No. 2012R1A3A2048814).
© The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.