Unveiling the Key Role of Aggregation in the Self-Doping of Conjugated Polyelectrolytes

Conjugated polyelectrolytes (CPEs) are a distinct class of polymers that feature a pi-conjugated backbone and pendant ionic groups, which confers them unique properties. In particular, since the discovery, during their purification in water, that some CPEs have the ability to be self-doped, they have attracted increasing interest from the organic electronics community. More recently, a self-acid doping mechanism was proposed after it was proven that the degree of doping can be modulated by the addition of an acid or a base. However, the explanation of both the self-doping and self-acid doping processes remains ambiguous, and their investigation continues to present significant challenges. In this work, we address the problem through a combination of experimental and computational techniques, including spectroscopy (UV-vis and Raman) and electrochemistry measurements in conjunction with DFT calculations and molecular dynamics simulations. We performed a comprehensive investigation into the self-doping mechanism of CPE-2K, poly [2,6-(4,4-bis-potassium butanylsulfonate-4H-cyclopenta-[2.1-b:3,4-b '] dithiophene)-alt-4,7-(2,1,3-benzothiazole)], and its homologue with only one alkyl ionic chain, CPE-K. Our findings point to a framework that integrates the self- and self-acid doping mechanisms into a unified one, in which backbone aggregation acts as the driving force.