Triazole-appended pyrano[2,3-c]pyrazolone based colorimetric chemosensors for recognition of Fe3+ ions and their molecular logic gate behavior

Abstract

Herein, two new triazole-appended pyrano[2,3-c]pyrazolone based colorimetric chemosensors (4a and 4b) have been designed and synthesized by a click-chemistry approach for recognition of Fe³⁺ and H₂PO₄⁻ ions. The chemosensors (4a and 4b) display excellent selectivity for Fe³⁺ ions in the presence of competitive metal ions with an instantaneous change in color that is perceptible to the naked eye. The selectivity and sensitivity of 4a and 4b were investigated through colorimetric and UV-vis studies in a mixed aqueous medium (MeOH/H₂O (8 : 2, v/v)). The binding constant (K_a) of chemosensor 4b for binding Fe³⁺ ions was determined to be 1.27 × 10³ M⁻¹ which is higher than that of chemosensor 4a (K_a = 5.9 × 10² M⁻¹). The binding mechanisms of 4a and 4b were investigated by ¹H NMR, FT-IR, HR-MS and UV-vis spectroscopy which were further supported by DFT studies. Moreover, 4a-Fe³⁺ and 4b-Fe³⁺ complexes were found to respond to H₂PO₄⁻ ions out of all other competitive anions. The chemosensor 4b was also found to be reversible for 4 cycles. Furthermore, the reversible colorimetric changes observed upon addition of Fe³⁺ and H₂PO₄⁻ ions to 4b were found to mimic an ‘INHIBIT’ molecular logic gate. The practical application of chemosensor 4b was also demonstrated successfully by evaluating the capability of the chemosensor to detect Fe³⁺ ions in real samples.