Optical properties of conjugated hydrophobic weak polyelectrolytes: Effects of pH, temperature and ionic strength

Abstract

ABSTRACTWe measure the UV-visible absorption of an annealed hydrophobic conjugated polyelectrolyte as a function of the pH, for different temperatures and ionic strengths. The position of the absorption maximum shifts non-monotonically as the neutralization degree f decreases from 1 to 0, thus defining two regimes. In the hydrophilic regime, 1>f>f1, the red shift is due to dominant direct Coulombic interactions between the charges along the backbone and the ? electrons, without significant conformational effects. In the hydrophobic regime,f1>f>0, the blue shift is dominated by conformational effects with two successive isosbestic points as f decreases. We propose two possible scenarios for the collapse of the chains at low neutralization degrees.