Boron-phenylpyrrin dyes: facile synthesis, structure, and pH-sensitive properties.

Boron-phenylpyrrin dyes: In the presence of BF3⋅OEt2, 4-(diethylamino)salicylaldehyde reacts with substituted pyrroles to give boron-phenylpyrrin dyes, which contain a central boron-containing seven-membered ring. Upon protonation in acidic solution, the complexes, with a large Stokes shift, exhibit a color change and a unique red shift in both the electronic absorption and fluorescence emission spectra (see picture), thus rendering them new analogues of boron-dipyrrin dyes that can be used as pH sensors.