Off-On–Off Cascade Recognition of Cyanide, Mercury, and Aluminum Using N/5-Monosubstituted Rhodanines

Abstract

This study aims to synthesize N-and 5-monosubstituted rhodanine derivatives as ion-sensing organics and investigate their sensing abilities. Following an easy and green approach to synthesis, the anion-sensing properties of the rhodanines were studied using colorimetric detection and spectroscopic methods. As a result of studies, rhodanines are found to be highly solventcontrolled colorimetric and fluorescent cyanide, mercury, and aluminum sensors. The stoichiometry of the interaction between CN − and both probes was determined to be 1:1 using Job's plot analysis. The binding constants (K s ) of CN − to 5-arylRh and N-arylRh were calculated to be 3.25 × 10 4 and 7.07 × 10 4 M −1 , respectively, demonstrating their high affinity for cyanide ions. The limits of detections for the 5-arylRh and N-arylRh were also determined as 356 and 617 nM, respectively. In addition to detecting CN − , 5-arylRh also serves as a specific turn-off sensor for mercury and aluminum when cyanide and hydroxide are present. This enables the fluorescence intensity to be toggled on/off by alternating the addition of CN − /OH − and Hg 2+ /Al 3+ . Furthermore, the LOD values for Hg 2+ and Al 3+ with 5-arylRh−CN − and 5-arylRh−OH − were determined to be 414 nM and 1.35 μM, respectively. Furthermore, the turn-on binding mechanisms of 5-arylRh and N-arylRh with cyanide ions were elucidated, and the experimental band gap (highest occupied molecular orbital/least unoccupied molecular orbital) energy values corroborated the proposed mechanism. Additionally, the interaction mechanism of the probes with CN − was further investigated by using the 1 H NMR technique. Collectively, these findings suggest that 5-arylRh, N-arylRh, and 5-arylRh−CN − hold promise as selective and sensitive candidate sensors for CN − , Hg 2+ , and Al 3+ ions.