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.