Fluorescence Studies on the Hydrophobic Association of Pyrene-Labeled Amphiphilic Hyperbranched Poly(sulfone−amine)s

Pyrene-labeled amphiphilic hyperbranched poly(sulfone−amine)s (Py-Am-HPSA) with a hydrophilic hyperbranched core and different amounts of hydrophobic tails were synthesized by end-capping of pyrene-labeled hyperbranched poly(sulfone−amine) (Py-HPSA) with palmitoyl chloride. The characterization of fluorescence showed that the excimer-to-monomer intensity ratio ( I E / I M ) increased with increasing content of hydrophobic units in polymers. In the range pH below 7, Py-Am-HPSA displayed the ordinary concentration-quenching effect of fluorescence for monomer emission and excimer emission, while the ratio of I E / I M monotonically increases with the increase of polymer concentration. With the rise of concentration of Py-Am-HPSA, I E / I M increases slightly and then significantly as it reaches the critical point where the concentration is 2−5 g/L. The acidity (or pH) of the aqueous solution has a great influence on the association behavior of Py-Am-HPSA. In the range pH 6.5−8, the ratio of I E / I M for Py-Am-HPSA increases dramatically with increasing pH, while that for Py-HPSA only varies a little.