Oxidative cyclization of N-acylhydrazones. Development of highly selective turn-on fluorescent chemodosimeters for Cu2+?

Organic & Biomolecular Chemistry Pub Date: 2008-11-10 DOI: 10.1039/B811612A

Abstract

A series of N-acylhydrazones were synthesised and found to be “turn-on” fluorescent chemodosimeters for Cu2+. Among the tested transition metal ions such as Cu2+, Pb2+, Zn2+, Cd2+, Hg2+, and Ni2+, a prominent fluorescence enhancement of up to 1000-fold was only observed for Cu2+ in acetonitrile (CH3CN). This was indicated by an onset of unprecedented structured emission. Detailed experiments established that the highly Cu2+ selective fluorescence enhancement resulted from an oxidative cyclization by Cu2+of the originally nonfluorescent N-acylhydrazones into highly fluorescent rigid 1,3,4-oxadiazoles, n-dope type blocks in optoelectronic materials. The chemodosimeters can be applied to sense Cu2+ at nM levels in CH3CN and sub-μM levels in neutral aqueous environments, despite a slower response in the latter case. It is expected that these redox-based chemodosimeters might be of general applicability.

Graphical abstract: Oxidative cyclization of N-acylhydrazones. Development of highly selective turn-on fluorescent chemodosimeters for Cu2+
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