From the UV–vis titration profiles (Fig. 4 and Fig. 5), the association constants for receptor 1–F− and 1–CN− in CH3CN were determined as 8.12 × 101 M−1 and 5.61 × 104 M−1 by the Hill equation, respectively. Job plot indicated a 1:1 complexation stoichiometry to receptor 1–F− and receptor 1–CN− (Figs. S3 and S4), respectively. Based on the UV–vis measurements, the detection limit of receptor 1 toward F− and CN− ion were determined to be 0.28 ppm and 0.41 ppm, respectively. The two detection limit values were sufficiently low to detect submicromolar concentration of the F− and CN−.