Spiropyran and spironaphthoxazine based opto-chemical probes for instant ion detection with high selectivity and sensitivity to trace amounts of cyanide

Abstract

Colorimetric chemical sensors with instant detection of cyanide ion, as a dangerous effluent from various industries and high toxicity, are nowadays of significant importance. Here, photochromic spironaphthoxazine (SNO) and hydroxyethyl spiropyran (SPOH) were synthesized and employed to detect some cations as well as trace amount of cyanide ion with reasonable selectivity and sensitivity among different anions. Their spiro forms were not triggered by metal cations, while their UV-induced open-ring isomers became susceptible to establish a dye-cation complex. The opto-chemical results demonstrated that neither SPOH nor SNO could make reliable discrimination between different metal cations, even after UV irradiation. However, both SPOH and SNO were selectively attached to CN− with a 1:1 stoichiometric ratio (from Job’s plot), even in the presence of several other anions and in the absence of UV irradiation. This was approved by 1HNMR and UV–vis spectroscopies. Besides, the interaction of CN− with SPOH and SNO was approved by visual color change from colorless (λmax of 345 nm for both) to dark yellow with λmaxs of 416 and 412 nm for those linked to hydroxyethyl merocyanine (MC-CN) and meronaphthoxazine (MNO-CN), respectively. The detection limits of SPOH (0.091 µM) and SNO (0.094 µM) sensors toward CN− were lower than its permitted level in drinking water by WHO (1.9 µM). These were also checked and compared with other spiro-based sensors. The obtained results demonstrate the potentiality of SNO and SPOH as promising colorimetric and opto-chemical sensors with wide linear dynamic detection range for determining trace amount of CN−.