A diketopyrrolopyrrole-based near-infrared sensor for selective recognition of fluoride ions

A new colorimetric and on-off fluorescence sensor based on diketopyrrolopyrrole (DPP) was synthesized for detection of fluoride anion. The sensor displayed a rapid responsivity and high selectivity and sensitivity toward F^- over other anions, with a significant 267 nm bathochromic shift of the absorption maximum, and the new peak was located in the near-infrared region. Meanwhile, it could be easily observed that the sensor for F^- ion changed from red to dark green by the naked eye, and from fluorescence red to non-fluorescence dark under UV lamp immediately after the F^- ion was added. The experimental results revealed that the formation of anionic species from deprotonation of the hydrazone N-H moiety by fluoride ion was responsible for the spectral changes. Density function theory calculations were conducted to rationalize the optical response of the sensor. To the best of our knowledge, it was the first sensor for fluoride ever reported with a 267 nm red shift response, which could give a colorimetric and on-off fluorescence response instantly.