Fluorescent Probe Investigation of a Water Soluble Polyphosphazene

Three fluorescent probes were utilized to investigate the microenvironment created by a water-soluble polyphosphazene copolymer in aqueous solution. The combination of intensity, wavelength shift, and vibrational analysis measurements of the three small-molecule probes is used to postulate an environment at high pH (with no added electrolyte) that is similar in polarity to methanol. In the absence of excess small-molecule electrolyte, negatively charged probes are repelled by the charge on the polymer. Addition of small-molecule electrolyte results in solubilization of the negatively charged probes. However, pyrene, even in the absence of added electrolyte (NaCl), is solubilized. Investigation of pyrene fluorescence quenching demonstrates the ability of the polyphosphazene copolymer to bind positively charged ions (Tl+) and repel negatively charged ions (I-). Neutral quenchers such as nitromethane readily penetrate the microenvironment of the polymer