Spectroscopic investigation on poly[bis(carboxylatophenoxy)]-phosphazene polyelectrolyte interactions with cationic dyes in dilute aqueous solution

The results of spectroscopic investigations on poly[bis(carboxylatophenoxy)]phosphazene, (NaPCPP), interactions with a cationic dye (methylene blue, MB) and with a cationic fluorescent probe ((1- dimethylaminonaphthalene 5-sulfonamidoethyl)trimethylammonium perchlorate, DA) in dilute aqueous solution are reported. The metachromatic behaviour and the DA fluorescence spectral perturbations induced by NaPCPP was measured as a function of polymer concentration and univalent added salt concentration and compared with that found using different, highly charged polyelectrolytes. NaPCPP is shown to strongly bind both dye molecules, with hydrophobic dye/polymer side chain interactions playing a significant role in the aggregation (at low polyelectrolyte/dye molar ratios, P/D) and redistribution (at high P/D values) of the dye molecules along the chains. The findings of this work are discussed also in the light of the results obtained in previous studies on other features of NaPCPP polyelectrolytic behaviour in dilute aqueous solution.