Near-infrared phosphorescent terpyridine osmium(II) photosensitizer complexes for photodynamic and photooxidation therapy

Osmium(II) complexes usually exhibit an excellent NIR (near-infrared) emission, which conforms to the optical window in a biological system. Here we designed three mitochondria-targeted NIR terpyridine Os(II) complexes as photosensitizers, which demonstrated great NIR phosphorescence emission and long phosphorescence lifetime. The emission spectra of the osmium(II) complexes were red-shifted with increasing conjugated planes of their terpyridine ligand (Os3 > Os2 > Os1). Furthermore, the Os(II) complexes, especially Os3, could produce singlet oxygen and oxidize NADH under both 465 nm and 633 nm LED light irradiation. It was found that Os3 has certain phototoxicities upon red light irradiation, and have great potential for NIR photodynamic therapy.