Enhanced fluorescence probes based on Schiff base for recognizing Cu2+ and effect of different substituents on spectra

Three enhanced fluorescence probes based on Rhodamine B-Schiff base structure were synthesized for detecting Cu2+. The corresponding detection limits were found to be 0.25 μM, 0.15 μM and 0.18 μM. Binding ratio and binding sites were determined by Job's and nuclear magnetic titration experiments. The binding constants obtained by the Benesi-Hildebrand equation to be 341.0 M−0.5,1.8 × 104 M−1, and 265.4 M−0.5, respectively. As isomers, the different effects of probes on Cu2+ detection were researched. By adjusting the position and the size of the substituent group, the effects of binding sites and steric hindrance on the complexation ratio, response time and detection limit were discussed. Optimal spatial combination structure with Cu2+ was obtained through energy calculation. Detection mechanism of Rhodamine B ring opening based on the complex of the Schiff base with Cu2+ was confirmed. E. coli staining and detection of real water samples had expanded their applications. Scheme of RB-1 and RB-2 detecting Cu2+ by different complexation sites and complexation forms. [Display omitted] •Three enhanced fluorescence probes for Cu2+ were synthesized.•The detection properties of Cu2+ were studied by fluorescence and ultraviolet spectra.•The influence of substituents on the detection was studied by DFT calculation, Job's and nuclear magnetic titration.•These probes were used for E. coli imaging and real water detection.