Colorimetric detection of Mn( ii ) based on a mixture of an anionic pyridylazo dye and a cationic polyelectrolyte in aqueous solution

We have developed a simple and valuable method for the construction of a colorimetric chemosensor for detecting Mn( ii ) in aqueous media. The chemosensor was prepared by mixing two commercial products, an anionic organic dye, 2‐(5‐nitro‐2‐pyridylazo)‐5‐( N ‐propyl‐ N ‐sulphopropylamino)phenol (Nitro‐PAPS) and a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC). Upon gradual addition of Mn( ii ) to the chemosensor, the absorption spectra showed a remarkable bathochromic shift concomitantly with a distinct colour change from yellow to blue‐green, while Nitro‐PAPS alone could not detect Mn( ii ) in a colorimetric method. PDADMAC played a key role in sensing Mn( ii ) for the mixture. The colour change might be due to the formation of the aggregate obtained through electrostatic interactions of a Nitro‐PAPS‐based Mn( ii ) complex with PDADMAC. This investigation can inform the development of a new chemosensor by the combination of an anionic dye and a cationic polyelectrolyte.