Novel pyrazoline and pyrazole “turn on” fluorescent sensors selective for Zn<sup>2+</sup>/Cd<sup>2+</sup> at <i>λ</i><sub>em</sub> 480 nm and Fe<sup>3+</sup>/Fe<sup>2+</sup> at <i>λ</i><sub>em</sub> 465 nm in MeCN
RSC advances