Synthesis of ¹⁸F-labeled phenolphthalein and naphtholphthalein

The fluorination of phenolphthalein and naphtholphthalein was performed with diluted fluorine gas under acidic conditions. For both compounds we observed an electrophilic fluorination into ortho position to the hydroxyl group. Through the use of this reaction we synthesized and characterized mono-and difluorinated derivatives of phenolphthalein and naphtholphthalein. The compounds were also prepared in the ¹⁸F labeled form, which are usable as a new type of probe for in vivo pH measurement in biological objects using Cerenkov imaging or combination of light absorption and PET.