A new spiropyran compound for selective naked-eye detection of copper ions in aqueous media and on test paper strips

Abstract

Using a strategy of modifying a bis(pyridin-2-ylmethyl) amino group in the 5-position, a new spiropyran dye ((1′-ethyl-3′,3′-dimethyl-N, N-bis(pyridin-2-ylmethyl) was synthesized. The dye was able to distinguish copper ions with remarkable selectivity by naked eye on paper strips and in aqueous media. Copper ions are selectively coupled to the receptor, which stimulates the opening of the spirocycle. Consequently, the π -electrons are localized on the spiropyran and a new absorption peak appears between 450 and 600 nm. Due to its functional properties, the receptor facilitates the rapid, selective, and sensitive detection of copper ions with a detection limit of 19 nM. According to Job's plot analysis, the correlation ratio between the probe and copper ions appears to be 2:1. Further, the probe was successfully applied to test papers strips that demonstrated distinct colors changes in response to different concentrations of copper ions.