Association behaviors of carbazole-labeled polyacrylamide in water studied by fluorescence spectroscopy

Abstract

In this work association behaviors of a carbazole-labeled hydrophobically modified polyacrylamide were studied by fluorescence spectroscopy in order to reveal the aggregation-induced spectral features. Both emission and excitation spectra reveal three distinct regimes for the association process of carbazole-labeled polyacrylamide with increasing concentration. In regime I, there is only a linear relationship between fluorescence intensity and concentration which was ascribed to unimer regime without aggregation. While a marked change in spectral shape could be observed in regimes II and III beyond the critical aggregation concentration. In regime II there is an aggregation-induced red shift in the excitation spectra and a decrease in 0–0 transition in emission spectra. In regime III aggregation-induced quenching was observed. These spectroscopic features of the excitation and emission spectra imply the formation of disordered J-aggregates by carbazole units during the association process, which could be employed to analyse the structural transition of hydrophobically modified polyacrylamide solutions.