Fig. 1. UV-Vis spectra of L4 with recognition metal ions
(a): CH₃CN/CH₂Cl₂=9:1, V/V;(b): CH₃CN/H₂O=8:2, V/V, pH=7.0

Fig. 2. UV-Vis spectra of L5 with recognition metal ions

Fig. 3. Fluorescence spectra of L4 with various metal ions
(a): CH₃CN/CH₂Cl₂=9:1, V/V;(b): CH₃CN/H₂O=8:2, V/V, pH=7.0

Fig. 4. Fluorescence spectra of L5 with various metal ions

Fig. 5. Fluorescence response of L4 with Cu²⁺
(a): CH₃CN/CH₂Cl₂=9:1, V/V;(b): CH₃CN/H₂O=8:2, V/V, pH=7.0

Fig. 6. Proposed mechanism for L4 and L5 recognizing metal ions