Studies on the dynamics of poly(carboxylic acids) with covalently bound thionine and phenosafranine in dilute aqueous solutions

Abstract

The poly(carboxylic acid) bound phenosafranine and thionine dyes show that, the fluorescence intensity and lifetime increases first and starts to decrease after reaching a maximum at pH 4.0. The fluorescence decay curve of the fluorophore bound polymers follow the biexponential decay fit independent of pH, while poly(MAA-Th) follows single exponential function above pH 4.0. At low pH, a more compact environment of the fluorophore exerts a more hydrophobic environment. In the subnanosecond time domain the solvation process is found to be incomplete while in the nanosecond time scale the solvation of the macromolecular chains is found to be over. The time resolved fluorescence spectra of the polymer bound fluorophores at different pH indicate distinct hydrophobic and hydrophilic environments due to the dynamics of the macromolecules in dilute aqueous solutions. For the first time structural transitions involving solvent are observed in the nanosecond and picosecond time domains for the same macromolecule.