The synthesis, crystal structure and enhanced blue fluorescence emission of novel antipyrine derivatives

Article abstract of DOI:10.1016/j.saa.2012.06.047

Four new antipyrine derivatives were synthesized and characterized by elemental analysis, FT-IR, ¹H NMR, ¹³C NMR spectroscopy, and a representative compound 1b was confirmed based on the X-ray crystallographic analysis. The antipyrine-phenylboronic acid 1b crystallizes in the monoclinic space group P2₁/c, and displays an E configuration about the CN double bond. The absorption and fluorescence spectra of these compounds were investigated. Replacement of a six-membered phenyl group with a five-membered thienyl unit in the antipyrine derivatives resulted in a bathochromic shift approximately 21 nm, while the bithienyl system caused a strong bathochromic effect of 53 nm relative to the substituted phenyl groups. The bithienyl-antipyrine hybrid 1c displayed a turn-on fluorescence response to water, acetic acid (HOAc) and sulfuric acid (H₂SO₄) in ethanol solution, but no fluorescence response toward alkali. Whereas the free compound was very weakly fluorescent in ethanol, the addition of water, HOAc and H₂SO₄ leads to an appearance of strong blue fluorescence and a dramatic increase of emission intensity.