Fluorescence Properties of Coumarin Laser Dyes in Aqueous Polymer Media.Chromophore Isolation in Poly(methacrylic acid) Hypercoils

摘要

The photophysical properties of a series of coumarin laser dyes in an aqueouspolyelectrolyte medium have been determined. The binding of the dyes to poly(methacrylic acid) (PMAA) in water has been demonstrated through the observation of a dramatic blue shift of fluorescence bands and increases in emission quantum yield, lifetime, and polarization. The systematic changes in fluorescence properties reveal that the hydrophobic dyes reside in relatively nonpolar (dry) and highly viscous microdomains for aqueous PMAA solutions at lower pH in which a compact conformation of the uncharged polyelectrolyte is important. The transition from a hypercoiled conformation (pH 4-8) can be followed readily by reference to coumarin fluorescence wavelength, quantum yield, or polarization data. Fluorescence parameters also serve as reporters of the low microscopic polarity and high viscosity of PMAA binding domains. Photophysical measurements are also reported for a coumarin moiety that has been covalently attached to the PMAA backbone. For the covalently bound dye, more subtle alterations of fluorescence properties are found over the entire range of pH examined, reflecting the close association with both compact and elongated (charged) forms of PMAA. jg p.2.