Novel polycyclic "turn-on" and "turn-off" pyrazoline and pyrazole fluorescent sensors for selective real-world monitoring of Fe(3+)/Fe(2+) in aqueous environments

Seven novel polycyclic pyrazoline and pyrazole sensors were synthesised and screened for useful photophysical properties with pyrazoline 2 and pyrazole 7, displaying an Fe(3+) "turn-off" response in aqueous environments with Fe(3+) limits of detection (LoD) of 2.12 μM and 3.41 μM, respectively. Both 2 and 7 sensors functioned in aqueous environments with real-world examples of Fe(3+) detection in tap water and mineral water samples. 2 and 7 are suitable for the detection of Fe(3+) at concentrations below the maximum iron limits for drinking water set by the Environmental Protection Agency (EPA) and European Union (EU).