Spiropyran-based triphenylamine AlEgens: pH-responsive and light-activated mitochondria-targeted fluorescence imaging

Mitochondria are important sites of energy metabolism in eukaryotic cells and are critical for cellular physiological functions, which are closely related to mitochondrial pH (∼8.0). In this work, novel smart-responsive fluorescent probes TOCy3 and MTOCy3 for visualizing pH changes in the mitochondrial microenvironment were prepared from spiropyran structures. TOCy3 and MTOCy3 exhibited good photochromic and photoelectric switching properties. Based on the fact that Spiropyran can be exchanged between open-ring merocyanine (MC) and Spiropyran (SP) forms under the irradiation of a short-wavelength laser light source during pH change, the structure forms a semicarbocyanine structure when the structure is MC, and the molecule is positively charged and the fluorescence is enhanced. As a result, cells can be "light up", thus enhancing cellular mitochondria-targeted fluorescence imaging under light control with a Pearson's coefficient from 0.49 → 0.88. In addition, the probe is characterized by low cytotoxicity, excellent cellular uptake, and good cell migration. At the microenvironmental pH of (∼8.0) or so, it showed the highest fluorescence intensity in solution and the stability of mitochondrial targeting in living cells, indicating that TOCy3 and MTOCy3 can be applied to detect changes in subcellular organellar mitochondrial pH in solution and living cells. Thus, it can be used to monitor specific dynamic changes associated with transitions in pathological and physiological states.