Synthesis and characterization of fluorinated derivatives of cresolsulfonphthalein

► We performed a reaction between 0.1% F2 and cresolsulfonphthalein in acidic media. ► We observed a specific fluorination into ortho positions to hydroxyl groups. ► All the fluorinated derivatives of cresolsulfonphthalein act like pH indicators. ► They have biologically relevant pKa 6.4-7.5 and absorption maxima at 582-592 nm. ► The reaction fits for synthesis of 18F-labeled indicators for in vivo pH detection.