Fluorescence Responses of the Protonation and Deprotonation Processes between Phenolate and Phenol within Rosamine

Two rosamine‐based pH probes 1a and 1b with pyronine‐phenol skeleton were designed and synthesized by a simple one‐step reaction. pH titration experiments showed that probes 1a and 1b exhibit near OFF–ON fluorescence responses around 550–750 nm towards the hydrogen ions. The pK_a of the probe 1a is 8.29, while that of the probe 1b increases to 12.1 because of the hydrogen bond inside it. Selective and competitive experiments indicated that both common ions and amino acids did not interfere their emission with hydrogen ions. Moreover, confocal fluorescent imaging showed that the probe 1a could be served as mitochondria biomarker in HeLa and Ges‐1 cells.