A Pyridine-bridged Bispyrrole Having N-Fluoroalkyl Imino Groups That Serves as Color and Spectroscopic Indicators of Perfluorocarboxylic Acids

Perfluoroalkylcarboxylic acids (PFCAs) have been produced in large quantities in industry around the world. Multiple C–F bonds on the alkyl chain allows them to exhibit high stability, high temperature resistance, and water and oil repellency. However, these properties also enhance their environmental persistence to result in bioaccumulation and biomagnification.^[1,2] With this reason, a convenient method to detect PFCAs in high sensitivity may play an important role to prevent the spread of environmental pollution. In this study, we newly designed a pyridine-bridged bispyrrole having N-fluoroalkyl imino groups (BPFI) that specifically serve as color and spectroscopic indicators of PFCAs.

We have synthesized BPFI from a pyridine-bridged bispyrrole having two formyl groups, which was synthesized through multi-step procedures, and 1H,1H-perfluorooctylamine. The product was characterized by means of NMR spectroscopy and mass spectrometry. In the UV-Vis absorption spectroscopy, BPFI showed the lowest energy absorption band at λ_max= 330 nm in CH₃CN. Although it showed no changes in color and spectrum upon mixing with common carboxylic acids such as acetic acid, and trichloroacetic acid, red-shift of the absorption band occurred upon mixing with PFCAs such as perfluoroheptanoic acid and heptadecafluoronanoic acid. BPFI also showed fluorescence with λ_max at 432 nm upon excitation at 320 nm. Its fluorescence intensity was slightly decreased upon mixing with the common carboxylic acids, but was dramatically decreased upon mixing with PFCAs. Further, color of the emission upon excitation at 365 nm with a commercially available handy UV light was specifically changed from blue to green upon mixing with PFCAs. We expect that BPFI will be a convenient reagent to detect PFCAs.

[1] S. Taniyasu, N. Yamashita, E. Yamazaki , G. Petrick, K. Kannan, Chemosphere, 2013, 90, 1686–1692.

[2] T. Stahl1, D. Mattern, H. Brunn, Environ. Sci. Eur. 2011, 23, 38.