Fluorescent macrocyclic chemosensor for Zn(II) detection at alkaline pH values

ABSTRACT

The new macrocyclic ligand L (28,29-dimethoxy-27-oxa-8,11,14,17,25,26-hexaazatetracyclo[22.2.1.1(2,6).1(19,23)]nonacosa-2,4,6(28),19,21,23(29),24,26(1)-octaene) has been synthesised. It contains a tetramine chain and the 2,5-bis(2-methoxy-3-metyl-phenyl)-1,3,4-oxadiazole (PPD-OMe) chromophore, acting as coordinating and sensing units, respectively.

The fluorescent emission of L depends on the pH being highly fluorescent at pH = 2 and not emitting from pH >10. The studies highlighted that L is a PET mediated emitting chemosensor, being the PET effect regulated by the degree of the tetraamine protonation.

L coordinates metal ions (Cu(II), Zn(II) and Cd(II)) in water giving rise to an OFF-ON fluorescent response for the presence of Zn(II) ion thus signalling its presence in the medium. This response is particularly notable at pH = 9 allowing to extend the Zn(II) sensing also in the alkaline pH field.

Graphical abstract

KEYWORDS:

• Zinc sensor
• Macrocycle
• 2,5-Diphenyl-1,3,4-oxadiazole
• 5-Diphenyl-1
• Fluorescence

Acknowledgments

The authors thank the Italian Ministero dell’Istruzione dell’Università e della Ricerca (MIUR) project 2015MP34H3 and Department of Pure and Applied Sciences of the University of Urbino (project DISPEA_FORMICA_PROG17, DISPEA_FUSI_PROG17, DISPEA_GIORGI_PROG18).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Ministero dell’Istruzione, dell’Università e della Ricerca [project 2015MP34H3].