pH‐Responsive Fluorescence Change Based on Dynamic Exchange between Emitting Aggregates and Quenching Monomers in Donor–Acceptor Dyes Bearing Carboxylic Acid Groups

pH imaging and measurement in biological systems is important because changes in pH are closely related with physiological and pathological processes. In this paper, a pH‐responsive fluorescence change based on the dynamic exchange between emitting aggregate state and quenching monomer state is reported. At low pH, the aggregate bearing a neutral carboxylic acid group in its protonated form continues to emit red light. In contrast, at high pH, the aggregate dissociates to the fluorescence‐quenching monomer owing to electrostatic repulsion among the anionic carboxylate moieties generated from the deprotonation process, resulting in a pH‐responsive change.