Water-Soluble Copolymers .36. Photophysical Investigations of Water-Soluble Copolymers of 2-(1-Naphthylacetamido)ethylacrylamide

A hydrolytically stable monomer, 2-(1-naphthylacetamido)ethylacrylamide (NAEAm), has been synthesized to utilize as a label in photophysical studies of copolymers with methacrylic and acrylic acid. An increase in excimer emission relative to monomer emission (I(E)/I(M)) is observed upon increasing solution pH. The hydrophobic character of both the naphthyl chromophores and the pendent methyl groups of MAA and the effective decoupling of the naphthyl chromophores from the polymer backbone via a spacer linkage are responsible for this behavior. The effects of NaCl, urea, and Triton X-100 surfactant on solution properties indicate that hydrophobic interactions among naphthyl chromophores are responsible for formation of an intramolecular hypercoil at high pH. Fluorescence measurements confirm the importance of coil dimensions and ion binding on quenching by nitromethane and copper(II) ions