Exclusive and Switchable Superoxide Radical Generation by O 2 -Capture-Based Electron Transfer and Supramolecular Assembly.

Type-I photosensitizers (PSs) can generate free radical anions with a broad diffusion range and powerful damage effect, rendering them highly desirable in various areas. However, it still remains a recognized challenge to develop pure Type-I PSs due to the inefficiency in producing oxygen radical anions through the collision of PSs with nearby substrates. In addition, regulating the generation of oxygen radical anions is also of great importance toward the control of photosensitizer (PS) activities on demand. Herein, a piperazine-based cationic Type-I PS (PPE-DPI) that exhibits efficient intersystem crossing and subsequently captures oxygen molecules through binding O 2 to the lone pair of nitrogen in piperazine is reported. The close spatial vicinity between O 2 and PPE-DPI strongly promotes the electron transfer reaction, ensuring the exclusive superoxide radical (O 2 •- ) generation via Type-I process. Particularly, PPE-DPI with cationic pyridine groups is able to associate with cucurbit[7]uril (CB[7]) through host-guest interactions. Thus, supramolecular assembly and disassembly are easily utilized to realize switchable O 2 •- generation. This switchable Type-I PS is successfully employed in photodynamic antibacterial control.