Fig. 6. (a) Fluorescence spectra of PBT in the presence of various anions. [PBT] = 10 μM, [An⁻] = 20 μM, 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: direct observation of fluorescence emission difference of the probe PBT (10 μM) under UV irradiation (365 nm) in the presence of different anions. Left to right: Cl⁻, Br⁻, I⁻, F⁻, NO₂⁻, CO₃²⁻, HCO₃⁻, ClO₄⁻, H₂PO₄⁻, SO₄²⁻ and AcO⁻. (b) The selectivity of PBT in the presence of various anions.