Exhaustive Syntheses of Naphthofluoresceins and Their Functions

Naphthofluorescein and/or seminaphthofluorescein derivatives possessing the additional benzene units to one or both sides of fluorescein were exhaustively constructed through Friedel-Crafts type reactions between corresponding aroylbenzoic acids and dihydroxynaphthalenes. Compound 4 works as a one-dye pH indicator, which shows red in strong acid condition and blue in basic solution. Compound 23 (diacetate of compound 4) shows good transitivity to the HEK 293 cells and acts as a fluorescent pigment for the living cell imaging. Compounds 5, 6, and 9 show fluorescent emission in the NIR region (>700 nm) and imply the potentialities of NIR fluorescent probes.