Experimental and computational study on the spectroscopic and colorimetric copper sensing behaviour of three ketimine derivatives

Abstract

Three imine based colorimetric copper sensors were successfully synthesized and their copper sensing behaviours characterized via absorption spectroscopy and rationalized by density functional theoretical (DFT) calculations. All three compounds interact strongly with copper in non-aqueous and semi- aqueous media, as indicated by the exergonic nature of this process: ΔGbinding = ∼ -28 kJ mol−1, which leads to a visible colour change; a process controlled by entropic effects in combination with the relative hardness of the binding sites. These compounds allow selective detection of copper at concentrations as low as 0.16 ppm with linear ranges of 1–5 ppm and quantification limits as low as 0.52 ppm. Whereas, only zinc leads to reduced accuracy for 2-[1-(2-hydroxyphenyl)ethylideneamino]phenol, at equimolar levels, for the other derivatives, hard-soft interactions allow significant interference from various metals, present at such a concentration. Overall, these compounds represent a viable starting point for the development of cheap colorimetric copper sensors.