In this paper, pH‐responsive fluorescent poly(amino ether ester)s with reversible “on–off” switching fluorescence and concentration‐dependent emission behavior were reported. A remarkable difference fluorescence behavior was observed at diverse polymer concentrations with pH values. Moreover, at all investigated concentrations, poly(amino ether ester)s can respond to acid pH and exhibit extreme acid‐induced fluorescence quenching phenomenon. Dynamic light scattering and transmission electron microscopy analyses confirmed that the fluorescence quenching phenomenon is due to the aggregation, which was caused by the protonation of tertiary amine groups in poly(amino ether ester)s under extreme acidic conditions. Interestingly, the quenched fluorescence can be completely recovered by adding an alkaline solution, thereby enabling an “on–off” switch function by adjusting the pH value. Most importantly, the pH‐responsive fluorescent poly(amino ether ester)s exhibit good biocompatibility and cellular imaging, and its cellular imaging function is highly sensitive to acid pH. Thus, this study opens a new idea for the preparation of amine‐based fluorescent polymers as stimuli‐responsive fluorescent probe for cellular imaging, drug delivery, and disease diagnostics.

Nontraditional small organic luminogens (NTSOLs) without classic conjugated chromophores have attracted significant attention. However, the design and synthesis of NTSOLs with fluorescence in the red region remain significantly challenging. In this study, we established a self‐catalyzed hydroxyl‐yne click reaction for preparing long‐wavelength and red‐emitting NTSOLs. Owing to their perfect reaction selectivity, high efficiency, and excellent universality, a series of compounds with well‐defined structures were obtained in high yields. Moreover, the obtained compounds showed concentration‐enhanced and excitation‐dependent emission characteristics. The compounds also exhibited dramatical chemical structure‐dependent and aggregation‐induced red‐shifted fluorescence properties, based on which we successfully obtained red‐emitting NTSOLs by simply adjusting chemical structure and concentration. Also, the compounds show good cell staining ability, which can be used in cell imaging.