Fig. 1: Type I and type II mechanism of ROS generation using photoexcited gold nanoclusters (upon one- and two-photon excitation).

CT charge transfer, ISC intersystem crossing, \({{{{{{{\rm{O}}}}}}}_{2}}^{\cdot -}\), superoxide anion, •OH hydroxyl radical, H₂O₂ hydrogen peroxide, ³O₂ triplet state oxygen (molecular oxygen), ¹O₂ singlet oxygen.