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Design and Synthesis of a Luminescent Cyclometalated Iridium(III) Complex Having N,N‑Diethylamino Group that Stains Acidic Intracellular Organelles and Induces Cell Death by Photoirradiation

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journal contribution
posted on 03.12.2012, 00:00 by Shinsuke Moromizato, Yosuke Hisamatsu, Toshihiro Suzuki, Yasuki Matsuo, Ryo Abe, Shin Aoki
Cyclometalated iridium­(III) complexes have received considerable attention and are important candidates for use as luminescent probes for cellular imaging because of their potential photophysical properties. We previously reported that fac-Ir­(atpy)3 4 (atpy = 2-(5′-amino-4′-tolyl)­pyridine) containing three amino groups at the 5′-position of the atpy ligand shows a maximum red emission (at around 600 nm) under neutral and basic conditions and a green emission (at 531 nm) at acidic pH (pH 3–4). In this Article, we report on the design and synthesis of a new pH-sensitive cyclometalated Ir­(III) complex containing a 2-(5′-N,N-diethylamino-4′-tolyl)­pyridine (deatpy) ligand, fac-Ir­(deatpy)3 5. The complex exhibits a considerable change in emission intensity between neutral and slightly acidic pH (pH 6.5–7.4). Luminescence microscopic studies using HeLa-S3 cells indicate that 5 can be used to selectively stain lysosome, an acidic organelle in cells. Moreover, complex 5 is capable of generating singlet oxygen in a pH-dependent manner and inducing the death of HeLa-S3 cells upon photoirradiation at 377 or 470 nm.