**4. Conclusion**

Conclusively, the comparative studies on the chemosensing property studies of the two Alizarin probes (**A3** and **AS3**) were successfully conducted. The two entities displayed closely similar behaviors towards the discrimination of cations and anions in CH3CN. However, variations in behaviors was observed in cations towards **A3** and **AS3**, where each probe was able detect certain cations, by means of UV–Vis absorption titrations, as well as fluorometric responses. The UV–Vis titration of **A3** with cations resulted in selective detection of Cu2+, Fe3+, Fe2+ and Zn2+, while **AS3** was responsive towards Cu2+, Fe3+, Fe2+, Ni2+ and Zn2+ respectively. The behaviors of anions towards **A3** and **AS3** in UV–Vis titrations (so as colorimetrically) and fluorometrically were consistently similar. On the hand, fluorometric titrations resulted in distinctive behaviors, where mostly fluorescence quenching effect was observed upon adding cations to **A3** or **AS3** in CH3CN. However, distinctive features were experienced upon adding Zn2+ to **A3** and **AS3**, where chelation fluorescence enhancement (CHEF) and chelation enhanced fluorescence quenching (CHEQ ) were observed, respectively. Another distinctive feature between the two probes observed was the deprotonation effects exhibited by **A3** upon interacting with anions (F<sup>−</sup> , CN− , OH− and AcO− ), where at first a quenching effect was observed, then further addition resulted in the enhancement effect (due to deprotonation effect). However, this was not the case for the with **AS3**, where all anions were restricted to fluorescence quenching ONLY, even after large quantities were added. The differences in fluorometric properties of **A3** and **AS3** towards Zn2+ and anions, were influenced by the presence of the sulfonyl group in **AS3**, which was the main determining factor, since it is a strong electron withdrawing group. Thus, it can be said that the two probes have displayed interesting features in applications towards the detection of cations and anions, which can be used in the development of analytical probes for real time applications.
