Influence of the molecular shape and shape-selective recognition on a three-component-based selective fluorescence probe. In the present contribution, we describe the synthesis of 3-hydroxycoumarin bearing a pyridyl group linked to the scaffold through an ester bond, which functions as a dual responsive fluorophore. In order to obtain a new fluorescent probe, this platform was conjugated to a polymerizable group allowing us to obtain a polymer. As a result, this study showed that the conjugation of polymerizable groups on the fluorescent probe may introduce new properties and thus expand the scope of applications in the field of chemosensors. In this article, we present some experimental and theoretical studies on the influence of the molecular shape on the optical properties, in particular the fluorescence anisotropy. The results showed that the two compounds display a different anisotropy. An original model based on the analysis of their molecular shapes was proposed to explain this finding. We have then demonstrated that this new fluorescent probe can be used as a three-component-based probe and its fluorescence quenching has shown to be selective towards different cations, based on the shape of the cation. Finally, we investigated the effect of the substituents (X and Y) at the pyridyl moiety (i.e. X = Br, Y = H, H, and H; X = Cl, Y = H; X = Cl, Y = Cl) on the selectivity of fluorescence quenching. The results showed that, in particular, the X substituents at the pyridyl moiety have a strong influence on the ion selectivity of the fluorophore. Indeed, the difference between the optical signal in the presence and in the absence of a metal is higher when X = H and Y = H (2-fold difference) than when X = Cl and Y = H (1.6-fold difference) than when X = Cl and Y = Cl (1.3-fold difference).