BIS(1-PYRENYLMETHYL) ETHER AS AN EXCIMER-FORMING PROBE OF HYDROPHOBICALLY MODIFIED POLY(N-ISOPROPYLACRYLAMIDES) IN WATER

The hydrophobic probe bis(1-pyrenylmethyl) ether [dipyme] shows intramolecular excimer fluorescence (intensity I(E)) in competition with fluorescence from locally excited pyrene chromophore ("monomer" emission, intensity I(M)). The intensity of the ratio I(E)/I(M) is sensitive to solvent viscosity. In addition the fine structure of the emission from locally excited pyrene is sensitive to solvent polarity. Dipyme has been used to investigate the fluidity and micropolarity of the polymeric micelles that exist in aqueous solutions of copolymers of N-isopropylacrylamide (NIPAM) and decyl-, tetradecyl-, or octadecyl-substituted acrylamides (NIPAM to N-alkylacrylamide molar ratios in the copolymers 100:1 and 200:1). Solutions of the copolymers in water exhibit an LCST. Fluorescence of dipyme dissolved in the polymeric micelles shows that macroscopic phase separation is accompanied by disruption of the hydrocarbon clusters. Potential artifacts associated with the use of dipyme in aqueous polymeric systems are discussed.