Recently, researchers have paid extensive attention to colorimetric/fluorimetric probe development and its applications in biological and industrial samples. The actual development of such probe molecules, however, often requires an iterative process to achieve certain goals such as selectivity and sensitivity toward a target analyte. In spite of growing interest in the development of practical molecular probes, there has not been much effort to implement the synthesis of detector molecules and the examination of their structure-reactivity relationship in undergraduate laboratories. A straightforward synthesis of copper probe molecules, which are systematically varied with aromatic substituents, is described to compare the reactivity toward copper(II) ion. The comparative kinetic study can readily visualize how the number and position of aromatic substituents affect the reactivity. This experiment is appropriate to demonstrate how mechanistic understanding will provide significant insight into rational design of practical colorimetric/fluorimetric probe molecules.