Two new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes (1 and 2) with piperazine subunits on position 3 or 5 were synthesized. Their absorption and steady-state fluorescence properties were investigated as a function of solvent. In water/MeCN (9:1, V/V) solution, the dyes show fluorescent enhancement upon increasing the acidity of the solution. They can be used in water/MeCN (9:1, V/V) solution as fluorescent pH probes excitable with visible light, with pKa values near-neutral (around 6.5 and 6.8). Dyes 1 and 2 are readily taken up by biological cells in the cytosol where it has no obvious toxic effects.
Deng, M., Yang, C., Gong, D., Iqbal, A., Tang, X. L., Liu, W. S., & Qin, W. W. (2016). BODIPY-derived piperazidine fluorescent near-neutral pH indicator and its bioimaging. Sensors and Actuators, B: Chemical, 232, 492–498. https://doi.org/10.1016/j.snb.2016.04.003