Synthesis and spectral properties of new boron dipyrromethene dyes

New BODIPY dyes have been synthesized via the condensation of R–CH2COCl (R = H, Br, Cl and Et2N) with 2,4-dimethylpyrrole and the coordination with BF3 etherate. The acetyl chlorides with electron-withdrawing substituents (R = Br or Cl) are easier to react with the 2,4-dimethylpyrrole to form the related dyes and make a red-shift in absorbance and fluorescence maximum. Dye 4 (R = Et2N), based on PET mechanism, exhibits good properties as a pH fluorescent sensor with a pKa of 8.74 and a 15-fold fluorescence enhancement in the pH range of 9.38–7.60.