Luminescence and Generation of Reactive Oxygen Species in Solution by Ta₆Br₁₂ Clusters

An intrinsic metal cluster NIR-II emission of the {Ta₆Br₁₂}²⁺ aqua/hydroxocomplexes was determined in aqueous solutions under inert atmosphere. The photoluminescence (PL) is enhanced in D₂O, and the lifetime scale expands from nanoseconds to microseconds. Possible cluster emission transitions have been assigned and analyzed from a computational perspective. In the presence of O₂, the cluster compound kept its robustness but showed partial quenching of the PL. Stern-Volmer and laser-flash photolysis studies confirmed that quenching is mainly associated with O₂ diffusion. Laser-flash photolysis experiments showed that singlet oxygen (¹O₂) was not detected under measurement conditions. Generation of peroxide and superoxide radical species after irradiation in D₂O was confirmed by using luminol as a probe, whereas no hydroxide radical species were detected as evidenced by the emission of the 3-coumarin carboxylic acid (3-CCA) molecular sensor.