Light‐intersecting Photoclick Reactions for Bioorthogonal Labeling on Single Cells: Dibenzo[<i>b</i>,<i>f</i>][1,4,5]thiadiazepine‐11,11‐dioxide as a Photoswitchable Reporter

Abstract The advancement of ring‐strain preloaded dipolaro‐/dienophiles plays a crucial role in bioorthogonal chemistry, enabling multiple high‐precision conjugations toward biomolecules simultaneously. However, durability of these ring‐strain preloaded reagents in vivo is a concern, as the ring‐strain is not reloadable once released during delivery process. In situ conversion of light‐energy into ring‐strain is a promising approach to ensure both biostability and spatiotemporal control endowed by light. Herein, we advance a seven‐membered cyclic azobenzene photoswitch, dibenzo[ b , f ][1,4,5]thiadiazepine‐11,11‐dioxide (DBTDD), bridged by a sulphone moiety. The photoisomerization from Z ‐DBTDD to ring‐strain‐loaded E ‐DBTDD enables an accelerated cycloaddition with various photogenerated dipoles to establish novel photoclick reactions, featuring a dual‐λ (405 nm+445 nm) synergistic control. In reactions with monoarylsydnones, a higher photo‐stationary ratio of E ‐DBTDD, achieved by varying the power density of 445 nm laser, presented an ultrafast cycloaddition rate ( k E =6.6×10 7 M −1 s −1 ) with a 13.8‐fold acceleration compared with Z ‐DBTDD, which is superior to established ring‐strain reporters (e.g., BCN‐OH, sTCO‐OH, DBTD). Then, bioorthogonal photoclick labeling of DBTDD tagged artificial phospholipid on living cell membranes was realized at subcellular resolution via an essential dual‐λ intersecting lithography with an elevated efficiency by adjusting the 445 nm power density.