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

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=6.6×10⁷ 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.