Phosphorescent Cyclometalated Iridium(III) Complexes Bearing Ethynyl-Extended 2-(2'-Hydroxyphenyl) Benzoxazole Ancillary Ligands

This article describes the synthesis and full photophysical studies at room and low temperature of a series of iridium(III) complexes incorporating an ethynyl-extended benzoxazole-based ancillary ligand. The electronic nature of the terminal end-group of the ancillary ligand was modulated by the simple introduction of electron-donating (Me, NBu) or -withdrawing (CN) groups. For all complexes, TD-DFT calculations showed that the lowest-lying transition was ligand-centered and that the nature of the first triplet state was very sensitive to electronic parameters leading to a charge transfer (CT) or locally excited (LE) excited state, always centered on the ancillary ligand. Singlet oxygen sensitization studies were performed on all compounds, showing that iridium(III) complexes containing cyano-functionalized ligands feature sensitization parameters, making them attractive candidates for photodynamic therapy.