Three fluorescent probes CdABA′, CdABA and ZnABA′, which are structural isomers of ZnABA, have been designed with N,N-bis(2-pyridylmethyl) ethylenediamine (BPEA) as chelator and 2-aminobenzamide as fluorophore. These probes can be divided into two groups: CdABA, CdABA′ for Cd²⁺ and ZnABA, ZnABA′ for Zn²⁺. Although there is little difference in their chemical structures, the two groups of probes exhibit totally different fluorescence properties for preference of Zn²⁺ or Cd²⁺. In the group of Zn²⁺ probes, ZnABA/ZnABA′ distinguish Zn²⁺ from Cd²⁺ with F_Zn²⁺–F_Cd²⁺ = 1.87–2.00. Upon interchanging the BPEA and carbamoyl groups on the aromatic ring of the fluorophore, the structures of ZnABA/ZnABA′ are converted into CdABA/CdABA′. Interestingly, the metal ions selectivity of CdABA/CdABA′ was switched to discriminate Cd²⁺ from Zn²⁺ with F_Cd²⁺–F_Zn²⁺ = 2.27–2.36, indicating that a small structural modification could lead to a remarkable change of the metal ion selectivity. ¹H NMR titration and ESI mass experiments demonstrated that these fluorescent probers exhibited different coordination modes for Zn²⁺ and Cd²⁺. With CdABA′ as an example, generally, upon addition of Cd²⁺, the fluorescence response possesses PET pathway to display no obvious shift of maximum λ_em in the absence or presence of Cd²⁺. However, an ICT pathway could be employed after adding Zn²⁺ into the CdABA′ solution, resulting in a distinct red-shift of maximal λ_em.