J -Aggregation-Reshaped pK a in a Spirocyclic BODIPY Enables Ratiometric Lysosomal pH Sensing and Super-Resolution Imaging

Abstract Ratiometric fluorescent pH probes typically rely on complex intramolecular energy/charge transfer, rendering the design strategies increasingly rigid. We report a conceptually distinct ratiometric probe based on pH-driven J-aggregate disassembly utilizing a spirocyclic BODIPY platform. Strategic installation of β-Cl and α-3,5-bis(trifluoromethyl)phenylvinyl substituents on BODIPY synergistically drives J-aggregate formation via directional X···π, F···H, and π···π interactions. The resulting J-aggregates and the corresponding monomer displayed markedly different pKa values (4.69 vs. 7.54, ΔpKa = 2.85). As pH increases, spirocyclization is triggered, driving the cooperative disassembly of the J-aggregates, while monomer emission remains constant, thereby enabling a robust ratiometric readout (I714/I654) with excellent reversibility. This supramolecular J-aggregate enables quantitative lysosomal pH detection in cells, diagnosis of acute gastritis in mice, and self-blinking super-resolution lysosomal imaging without exogenous additives. This work establishes a new paradigm for ratiometric probe design via aggregation control and stimulus-responsive supramolecular disassembly.