Cucurbit[8]Uril-Stabilized Charge Transfer: An Efficient Supramolecular Approach Toward a Heterogeneous Organic...

Host-stabilized charge transfer (HSCT) has been widely utilized in macrocycle-derived supramolecular assemblies and architectures. However, there has been less research attention focused on the direct fabrication of pure organic photocatalysts using HSCT. Herein, four viologen derivatives (m-PV²⁺, m-BPV²⁺, d-PV²⁺, and d-BPV²⁺) with different electron donor-acceptor (D-A) structures were synthesized. Their host-guest complexes with cucurbit[8]uril (Q[8]) in an aqueous solution could be switched using the substituted electron donor moieties, in which the host-guest complexes of m-BPV²⁺@Q[8] and d-BPV²⁺@Q[8] exhibited HSCT interactions. Control experiments revealed that the d-BPV²⁺@Q[8] complex had the strongest ability to sensitize singlet oxygen (¹O₂). This was ascribed to the increased π-conjugation of d-BPV²⁺@Q[8], which led to more effective HSCT upon encapsulation by the Q[8] host. Consequently, the d-BPV²⁺@Q[8] complex could be easily employed as a heterogeneous photocatalyst for the photooxidation reaction of thioether com-pounds with high selectivity. In particular, d-BPV²⁺@Q[8] was successfully applied to the synthesis of sulfoxide drugs, such as the con-version of inexpensive Iberverin ($7.0 per gram) to the expensive bioactive inhibitor Iberin ($19500.0 per gram) in high yield (94 %).