Azobenzene disperse dye-based colorimetric probe for naked eye detection of Cu2+ in aqueous media: Spectral properties, theoretical insights, and applications

A sensitive colorimetric probe (MRP) was developed by combination of m-methyl red dye-based signalling unit and tridentate chelating moiety. The sensor exhibits high selectivity toward Cu2+ over other common metal ions, displaying a dramatic color change from light yellow to red in the presence of Cu2+ in aqueous media with a physiological pH range. Detailed spectral investigations and mass spectrometry provided corroborative evidence in support of two-step complexation process (2:1 and 1:1 stoichiometry for MRP and Cu2+ in turn) by Jahn-Teller effect in the titration experiments. The drastic red-shift nature of the MRP + Cu2+ can be assigned to intramolecular charge transfer (ICT) and metal-to-ligand charge-transfer (MLCT). Additionally, the electronic structures and sensing mechanisms of MRP with Cu2+ were calculated by density functional theory (DFT/TDDFT) calculations. Moreover, using this azo disperse dye-based probe, MRP could be used to monitor Cu2+ adsorbed on live bacteria using an optical microscope. (C) 2017 Elsevier B.V. All rights reserved.