Synthesis of pH-responsive cyclometalated iridium(III) complex and its application in the selective killing of cancerous cells.

Cyclometalated iridium(III) complexes are promising candidates as photosensitizers (PSs) in photodynamic therapy (PDT). The challenge in PDT is the selective killing of cancerous cells over the neighboring normal cells. In this work, a pH-responsive cyclometalated iridium(III) complex (probe 1) was designed and synthesized as an effective PS to selectively kill cancerous cells, with 3-(2-pyridyl)benzaldehyde used as the main ligand and 1-(2-pyridyl)-β-carboline used as an ancillary ligand. Probe 1 shows enhanced photoluminescence emission and higher 1O2 quantum yield in an acidic environment compared to a neutral solution, which led to remarkable phototoxicity toward cancerous cells and high selectivity for killing cancerous cells over normal cells within 10 min. This work demonstrates that the cyclometalated iridium(III) complex with acidic pH-responsive photoluminescence emission and high 1O2 generation is an effective alternative PS for selectively killing cancerous cells.