Novel pyrazoline and pyrazole “turn on” fluorescent sensors selective for Zn2+/Cd2+ at λem 480 nm and Fe3+/Fe2+ at λem 465 nm in MeCN

Abstract

A small series of simple pyrazoline and pyrazole based sensors, all derived from the same chalcone precursors, were synthesised, characterised and screened for their fluorescence “turn on” properties in the presence of multiple metals. Pyrazole 8 displayed an excellent fluorescence profile with approx. 20× fold increase in λ_em 480 nm with Zn²⁺ compared to a 2.5× fold increase with Cd²⁺. Pyrazole 9 displayed a 30× fold increase at λ_em 465 nm for Fe³⁺ compared to Fe²⁺ with a Fe³⁺ limit of detection of 0.025 μM. The corresponding pyrazolines displayed contrasting properties with important implications for future pyrazoline and pyrazole sensor design.