A cucurbit[8]uril-triggered ionic photosensitizer in solution and solid states: selective control of ¹O₂ and O₂˙^-...

Selective control of reactive oxygen species (ROS) generation captures the imagination of scientists because of its broad potential applications in photochemical reactions and biomedicine. Herein, we develop a novel supramolecular method enabling selective control of ¹O₂ and O₂˙^- generation based on host-guest assembly in solution and the solid state. The cationic guest G-I (Cl^- as counteranions) lacks the ability to sensitize ROS but is transformed into an efficient organic photosensitizer through face-to-face dimerization within the cucurbit[8]uril (Q[8] or CB[8]) cavity via host-guest interactions. Although the G-I@Q[8] complex retains an identical assembly structure in both solution and solid-state phases, the differing electron transfer pathways of Cl^- counteranions between phases result in selective control of ¹O₂ and O₂˙^- generation. This control is readily achievable by employing the host-guest complex as homogeneous or heterogeneous photocatalysts. Importantly, X-ray structural analysis reveals that the dimerized G-I@Q[8] framework exhibits remarkable formaldehyde (HCHO) adsorption capability due to the outer-surface interactions of the Q[8] host, enabling the solid G-I@Q[8] complex to serve as a highly efficient adsorption-photocatalytic platform for HCHO remediation. This study advances our understanding of macrocycle-mediated host-guest assembly in controlling ROS generation and photocatalysts with multiple functions.