Abstract: The development of colorimetric chemosensors is an area in great expansion due to the simplicity of assay and lower cost compared with others sensing methods. Sensing devices for the analysis of toxic or heavy metal ions play an important role in clinical toxicology, environmental, bioorganic chemistry, bioremediation, and waste management. Until now, most of the chemosensors developed involve laborious and expensive procedures and there is an interest in strategies for single step synthesis, optimizing the efficiency of the chemical reaction and avoiding time-consuming processes of separation and purification. Therefore, the development of a small molecule-based colorimetric chemosensors with simple synthetic and isolation procedures has received much attention in the last decade. The current interest in azine derivatives arises from their wide range of applications in diverse areas such as material and environmental sciences, biomedical, analytical, supramolecular chemistry and catalysis. Additionally, azine ligands bearing N, O and S heteroatoms in their structure should exhibit improved coordination ability. Following our previous work, azine ligands functionalized with heterocycles such as thiophene L1, pyrrole L2 and furan L3, were used in a cation chemosensory study in ACN and ACN-water mixtures. L2 exhibited a selective and high sensitive colorimetric response in the presence of Hg(II) and Pd(II) (colourless to yellow or colourless to orange, respectively).Acknowledgements: thanks are due to FCT and FEDER (European Fund for Regional Development)-COMPETE-QREN-EU for financial support to the research center, CQ/UM [PEst-C/QUI/UI0686/2013 (F-COMP-01-0124-FEDER-037302). FCT is also acknowledged for financial support to the NMR Portuguese network (PTNMR, Bruker Avance III 400-Univ. Minho) and for the post-doctoral grant of R.M.F. Batista (SFRH/BPD/79333/2011). We are also grateful to the Instituto da Educação of Universidade do Minho for providing the laboratory infrastructure necessary for the development of this work.