Two in One: Luminescence Imaging and 730 nm Continuous Wave Laser Driven Photodynamic Therapy of Iridium Complexes

Abstract

A phosphorescent cationic iridium complex (1) with a donor−π-donor type unit as a N∧N ligand and 2-phenylpyridine as a C∧N ligand was synthesized and characterized. 1 exhibits an intense absorption peak centered at ∼450 nm with a large molar extinction coefficient (ε) of ∼2.4 × 104 M–1 cm–1 and displays highly efficient orange-red phosphorescence located at 620 nm with a quantum efficiency of ∼3% in PBS buffer solution at room temperature, which is beneficial for a luminescence probe in living cells excited by visible light. Importantly, the generation of singlet oxygen (1O2) by 1 was observed by 730 nm continuous wave (CW) laser irradiation owing to its reverse saturable absorption property, which was confirmed by the 1O2 scavenger of 1,3-diphenylbenzo[c]furan (DPBF) and ESR spectra. The photodynamic therapy effect of 1 in vivo by a 730 nm CW laser was further assessed by histological examination and immunohistochemistry.