Cyanide Sensing by 5‐Halo‐2,2′‐Bithiophene‐5‐Carboxaldehyde Nanomaterials: Effect of Halogenation and Density Functional Theory Studies

The development of efficient strategies for the detection of cyanide ions simply and cost‐effectively is significant in contemporary research. Novel design principle for efficient visual and fluorometric sensing methods for cyanide ions using halogenated (Br, I) organic nanomaterials of 2,2′‐bithiophene‐5‐carboxaldehyde was developed, and the effects of the number of halogen substituents on sensing were analyzed. Quantitative analysis of cyanide sensing by 5′‐Iodo‐2,2′‐bithiophene‐5‐carboxaldehyde revealed that the binding constant is 1.38 × 10 ³ M ⁻¹ at room temperature. The limit of detection (LOD) and the limit of quantification (LOQ) were determined to be 3.52 × 10 ⁻⁵ M and 0.17 × 10 ⁻⁵ M, respectively. Additionally, Job's plot revealed 1:1 stoichiometric binding between 5′‐Iodo‐2,2′bithiophene‐5‐carboxaldehyde and cyanide ion. Halogen bond and π–π stacking interaction mediated assembly of 5′‐Iodo‐2,2′‐bithiophene‐5‐carboxaldehyde was obtained from single crystal X‐ray diffraction studies. Noncovalent interaction‐mediated self‐assembly of the sensor resulted in spherical nanostructures, as evident from transmission electron microscopy (TEM). Importantly, density functional theory (DFT) studies showed that by increasing the number of halogen substitutions (Br, I) on 2,2′‐bithiophene‐5‐carboxaldehyde, the activation energy for the nucleophilic attack of cyanide to the aldehyde moiety decreases, and thereby the cyanide sensing efficiency increases.