Mechanical-Bond-Enabled Highly Efficient Charge Separation in a Light-Harvesting Hetero[2]Catenane

Photodriven charge separation is a key process for converting solar energy into chemical energy. However, it remains a challenge to develop artificial light-harvesting materials that can simultaneously achieve ultrafast charge separation and a long-lived charge-separated state with low energy loss. In contrast to conventional strategies based on covalent or noncovalent interactions, we employed a mechanical bond to forcibly assemble two strongly electron-deficient cationic chromophores (TTzBox⁴⁺ and PDI-C²⁺), which have very similar reduction potentials and exhibit limited noncovalent interactions, into a hetero[2]catenane (TTzPCat⁶⁺). This design provides efficient π electronic couplings, enabling ultrafast charge separation (<2.3 ps) even with a low driving force (|ΔG_CS| ≈ 160 meV). Furthermore, the adaptive molecular conformation of TTzPCat⁶⁺, in combination with the Marcus inverted region effect, successfully prolongs the charge-separated state lifetime (k_CS/k_CR > 1000), surpassing the conventional trade-off between driving force and charge separation efficiency in heterogeneous donor-acceptor systems. The photocatalytic system based on TTzPCat⁶⁺ exhibits an over 2-fold enhancement in selective oxidation of aryl sulfides under mild conditions, demonstrating the potential of mechanical bonding for preparing photocatalytic materials. This investigation not only highlights a strategy for achieving highly efficient charge separation with low energy loss but also offers fresh insights into developing efficient solar energy conversion systems.