Substituent effect on colorimetric detection of biologically and environmentally relevant anions: Insight in real-life applications.

A new set of chromogenic anion receptors R1-R4 have been synthesized with a different substituent, including electron withdrawing (nitro moiety in R1), conjugated group (naphthyl in R2), and electron donating (methyl in R3), respectively. The receptors R1-R4 exhibited very good sensitivity towards the F and AcO anions in the DMSO. In addition, R1 showed selectivity towards HPO ions over other tested anions. R1 especially acted as an effective sensor for sodium salts of F, AcO, AsO, and AsO ions in an aqueous medium due to the presence of two electron-withdrawing nitro substituents, which showed hydrogen bond donor tendency and acidity of the OH proton. This result indicates that R1 is highly capable of competing with an aqueous medium to detect anions without counter Na ion interference. Interestingly, R1 displays solvatochromic property in the presence of AcO ions in different aprotic solvents. Additionally, the receptor R1 shows high binding affinity towards AcO ions in the buffer medium (DMSO: HEPES, 9:1 v/v), which displayed remarkable colour change from pale yellow to blue with a large ∆λ of 170 nm. The CV studies reveal the deprotonation of the -NH proton upon interaction with the AcO ions. The receptor R1 is subjected to practical application to sense F and AsO ions using the test strip. In addition, the receptor R1 proves itself as a potential applicant for the detection of F ions quantitatively in commercially available mouthwash.