Fig. 3. The fluorescence spectra of PBT in the absence and presence of F⁻, [PBT is 10 μM], [F⁻ is 20 μM], [Tris buffer is 20 mM] in a mixture of THF and Tris buffer solution (pH 8.0), (1 : 9, v/v). λ_ex = 335 nm, λ_em = 470 nm. Inset: The fluorescence colour change of PBT in the absence and presence of F⁻.