The design and synthesis of new chemosensors for the detection of trivalent cations represent a high interest area into the supramolecular chemistry. The detection and quantification of metallic ions is applied to many fields. In that direction, two derivatives of the bis-vainilline condensed in positions 3- and 3’- with hydralazine and isoniazide respectively, have been analyzed as potential sensors of trivalent cations. The structural geometry and the stability of both substances was determined using the DFT theory. In presence of Al³⁺ the structural differences between both compounds have a great influence in its fluorescents properties which can be explained with to the decrease in the dihedral angle. Moreover, the ΔE values as a consequence of the coupling with the cation Al³⁺ indicate that the energy difference between the HOMO and the LUMO declines, improving the stability of these systems. In the other hand, both compounds display a strong improvement of the signal intensity when Cr³⁺ was used, while when Fe³⁺ was employed with the first ligand a quenching effect was observed. Finally, it is necessary to consider that a mixture of both substances can be used to discriminate between Fe³⁺, Al³⁺, and Cr³⁺.