Singlet Oxygen Generation Driven by Sulfide Ligand Exchange on Porphyrin–Gold Nanoparticle Conjugates

Here, we report a switching method of singlet oxygen ((1)O(2)) generation based on the adsorption/desorption of porphyrins to gold nanoparticles driven by sulfide (thiol or disulfide) compounds. The generation of (1)O(2) by photosensitization is effectively suppressed by the gold nanoparticles and can be restored by a sulfide ligand exchange reaction. The on/off ratio of (1)O(2) quantum yield (Φ(Δ)) reached 7.4. By examining various incoming sulfide compounds, it was found that the ligand exchange reaction on the gold nanoparticle surface could be thermodynamically or kinetically controlled. The remaining gold nanoparticles in the system still suppress the generation of (1)O(2), which can be precipitated out simultaneously with porphyrin desorption by the proper polarity choice of the incoming sulfide to restore the (1)O(2) generation.