Host–Guest Charge Transfer Mediated Disequilibration of Stilbenes Inside a Water-Soluble Nanocage

Stilbenes are prototypical photoswitches due to their pronounced photoinduced structural changes and robust thermal stability. However, a narrow window of excitation in the UV range, formation of photostationary states (PSS), low quantum yields, and photochemical side-products have significantly constrained their practical applications. Here, we leverage nanoconfinement-driven chemistry to achieve ultrafast, high-efficiency <i>cis</i>-to-<i>trans</i> isomerization of stilbenes in aqueous media. The selective encapsulation of <i>cis</i>-stilbene derivatives compared to their <i>trans</i>-versions within the water-soluble nanocage Pd₆L₄¹²⁺ induces host-guest charge-transfer interactions, enabling visible-light-mediated photoisomerization without PSS formation. Broadband femtosecond transient absorption spectroscopy provided direct signatures of <i>cis</i>-stilbene radical cation and allowed us to track the isomerization dynamics, occurring on ultrafast time scales in tens of picoseconds. Computationally derived optical signatures along with low-temperature electron paramagnetic resonance spectroscopy further validate the radical cation-mediated isomerization pathway. This work presents the first sensitizer-free strategy for driving stilbene photoisomerization out of equilibrium using visible light in aqueous environments, broadening the scope of charge-transfer-driven photochemical transformations.