Colorimetric chemodosimeter for cyanide detection based on spiropyran derivative and its thermodynamic studies

• We synthesized a chemodosimeter 5 based on spiropyran derivative for CN− detection.
• 5 was found with high selectivity to CN− even in the presence of halide ions.
• Only by adding CN− to 5 in DMSO, 5 underwent a ring-opening reaction.
• The rate constants of ring-opening were investigated at different temperatures.
• Recovery of 5 was achieved by adding Cu2+ due to the formation of [Cu(CN)x]n−.

A colorimetric chemodosimeter based on a spiropyran–azosalicylal conjugated structure has been synthesized and investigated with high selectivity and sensitivity toward cyanide anions. This spiropyran derivative and cyanide anions form a 1:1 stoichiometry confirmed by Job's plot method. By absorption spectroscopy experiments at different temperatures and 1H NMR titration experiment, the ring-opening mechanism has been determined as that the ring-opening course only arises when cyanide anion is present. However, higher temperature can lead to a higher ring-opening constant related to a faster color changing rate, which is identical to the results of the absorbance/time-responding experiment. Furthermore, the behavior that by the addition of copper cations(II) to the complex of spiropyran and cyanide anion (1:1) the recovery that takes place on absorption spectra due to the formation of copper cyanides, makes spiropyran be possibly used as a molecular switch.

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