Morphology controllable fabrication of poly-o-phenylenediamine microstructures tuned by the ionic strength and their applications in pH sensors

We report a one-recipe-various-structure method to prepare poly(o-phenylenediamine) (PoPD) microstructures. The assembly units, i.e., PoPD oligomers, were formed in the presence of a low redox potential oxidant of CuCl₂. The further assembly process of the oligomers was triggered by the introduction of concentrated NaCl solution. The belts, bow-tie-shaped microstructures and clusters of PoPD were fabricated in a controlled manner by varying the concentration of NaCl and oPD. The introduction of NaCl is believed to influence the hydrogen bonding behaviour of PoPD oligomers. The morphology and optical properties were influenced by acidic or basic treatment. Interestingly, the belts after treating with NaOH produce strong fluorescence emission. A pH sensor based on this property was developed.