Indole-azadiene conjugate as a colorimetric and fluorometric probe for selective fluoride ion sensing

An indole-azadiene conjugate (1), synthesized by facile one-step condensation, behaves as a highly selective probe for detection of fluoride ion both in colorimetric and fluorometric analyses. The probe 1 shows F⁻-selective color change from colorless to yellow and appearance of green fluorescence. ¹H NMR analysis and ab initio calculation reveal that the F⁻-induced colorimetric and fluorometric responses of 1 are simply driven by hydrogen bonding interaction between the indolic NH protons and F⁻.