Schiff base fluorescence probes for Cu2+ based on imidazole and benzimidazole

• Two new Schiff base fluorescence probes were designed and synthesized.
• Theoretical calculations showed the compounds could coordinate with metal ions.
• Experiments showed that the compounds have outstanding fluorescence properties.
• The fluorescence probes exhibited excellent sensitivity and selectivity for Cu2+.

Two novel Schiff base fluorescence probes for Cu2+ were designed and synthesized by reactions between p-fluorobenzaldehyde, p-phenylenediamine and heterocyclic compound (including imidazole and benzimidazole). The optimized geometries, frontier orbitals, molecular orbital contributions and excitation energies for the probes were predicted at B3LYP/6-31G* by theoretical calculation. And the probes were characterized by FTIR, 1H NMR, UV–vis and fluorescence spectroscopy. Test results showed the probes had a high selectivity for Cu2+ compared to other metal ions measured (Ag+, Co2+, Mg2+, Ni2+, Pb2+, Zn2+, Cd2+ and Fe3+). From test results, a high selectivity for Cu2+ was discovered in this type of probes, especially, the probe based on benzimidazole exhibited more significant enhancement in fluorescence intensity compared with imidazole-based due to its relative large conjugate rigid plane structure. The detection mechanism of the synthesized probes with high selectivity for Cu2+ was also discussed.

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