pH-Sensitive perylene tetra-(alkoxycarbonyl) probes for live cell imaging

A fluorescent pH-sensitive probe, 1-hydroxyl-3,4;9,10-tetra(n-butoxyloxycarbonyl)perylene (HPTBAC), was synthesized and used for pH sensing in living cells. The probe exhibits fluorescence emission characteristics with a pKa value of 7.9 and linear response to the very important pH range of 6.7–8.9. We designed a probe for binding the O− of hydroxyl in the perylene skeleton with H+ to possess the probing capability for detection in the acid to weak base pH range. The pH sensitivity is introduced via the O− moiety upon either protonation or deprotonation. In the deprotonation form, HPTBAC exhibits very weak emission due to strong electron-donating groups of O−. HPTBAC was successfully applied as a high-performance fluorochrome for living A549 cell (human lung cancer) and E. coli cell imaging. The results demonstrate that as a pH probe, HPTBAC is a good candidate for monitoring pH fluctuations in living cells.