Amphiphilic copolymers of some aromatic vinyl compounds and an electrolytic monomer as potential media for photosensitized electron transfer: Fluorescence quenching by an amphiphilic electron acceptor in aqueous media

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Abstract
Amphiphilic polymers were prepared by the copolymerization of 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) and aromatic vinyl compounds such as 9‐vinylphenanthrene (VPh) and 1‐vinylpyrene (VPy) with the expectation that they would serve as potential media for photosensitized electron transfer reactions. AMPS strongly solubilizes the hydrophobic segments into water; i.e., poly(AMPS‐co‐VPh) with VPh mole fraction (fPh) up to about 0.60 and poly(AMPS‐co‐VPy) with VPy mole fraction (fPy) up to about 0.35 were found to be soluble in water. Poly(AMPS‐co‐VPh) in aqueous solution, as compared with that in DMF solution, showed a broad fluorescence spectrum with significant tailing in the longer‐wavelength region along with a decrease in the intensity of the structured, monomer fluorescence band. These phenomena seem to imply the presence of an excimerlike interaction of phenanthryl groups in an aqueous solution through which the fluorescence from excited VPh units may be partly self‐quenched. A considerable enhancement of the fluorescence from sodium 8‐anilino‐1‐naphthalenesulfonate (ANS) caused by hydrophobic interaction of the probe with poly(AMPS‐co‐VPh) in aqueous solution indicated that these copolymers assume micellar structures. The fluorescence of these copolymers in aqueous solutions was quenched by bis(2‐hydroxyethyl)terephthalate (BHET), an amphiphilic quencher, far more effectively than by fumaric acid, a hydrophilic quencher. This tendency is particularly strong for the copolymers with higher content of hydrophobic units. The second‐order rate constants for the quenching of poly(AMPS‐co‐VPh) (fPh = 0.58) by BHET were found to be ca. 3 × 1010 and 1.5 × 109 M−1 s−1 in aqueous and in DMF solution, respectively. The larger value in an aqueous solution is presumably due to an increase of the effective concentration of the amphiphilic quencher around the VPh sequences of the copolymer resulting from hydrophobic interaction.