Colorimetric sensing of cyanide ion by pyromellitic diimides synthesized in one step from commercially available reactants

Abstract

Several pyromellitic diimides (PMDIs) containing different groups including thiol, carboxyl, hydroxyl, and alkyl as N-substituent were synthesized from commercially available reactants in one step, and their interactions with anions like CN¯ and F¯ were studied. The investigation indicated that the anions more basic than RS¯ trigger generation of colorful radical anion in diimides bearing thiol group as N-substituent. The study of mechanism using various techniques such as spectroelectrochemical analysis and UV–vis spectroscopy suggested deprotonation of thiol by anion, followed by electron transfer (ET) from thiolate ion to carbonyl as a probable mechanism. The proposed mechanism was further approved through theoretical study. The geometry optimization of diimide/CN¯ system resulted in complete deprotonation of thiol by CN¯ as a stable structure. Also, the calculation of HOMO and LUMO levels for diimide, its anion, and CN¯ showed that deprotonation make intramolecular ET more feasible, while decreasing the probability of intermolecular ET. Thereafter, in order to develop a new sensor for CN¯, the selectivity and sensitivity of diimides possessing thiol group were tested. The results indicated that although these diimides can be applied as a sensor to differentiate CN¯ from many anions at a micro-level concentration, they undergo the same reaction with any anion more basic than HS¯. The present study did not only introduce a novel indicator for CN¯ (or any anion more basic than RS¯), but also provided new insights into the interaction of anions with aromatic diimides (ADs).