A new class of three 2,4-thiazolidinedione based macrocycles (3a–c) have been synthesized and then characterized from spectral data and X-ray crystallography. The fluorescence quenching of the compounds caused by the addition of nineteen separate metal cations to their solutions in ethanol–water (3 : 1) was investigated, when it was observed that among the cations, the response to Fe³⁺ was distinctive. Again, among the macrocycles, 3c gave the best result.