Unveiling the molecular features of p- and n-doped polyfluorene

The electrochemical doping processes of poly(9,9-dioctylfluorene) (PFO) films have been studied by a combination of vibrational and electronic spectroscopy with electrochemical methods in acetonitrile. This analysis provided a comprehensive understanding of the distinct mechanisms governing p- and n-doping and revealed the molecular nature of their respective charge carriers. P-doping induces substantial structural and optical transformations, including the formation of polaronic and quinoid domains, and is accompanied by strong interactions between the polymer and solvent molecules. In contrast, n-doping shows lower solvent interaction, faster charge equilibration, and limited structural reorganization. A key finding is that polaron compression phenomena occur exclusively under p-doping, due to inter-polaron interactions at higher doping levels. These results reveal the asymmetric roles of solvent and charge compensation in the two doping regimes and contribute to a deeper understanding of the electronic, structural, and dynamic behavior of PFO during reversible electrochemical doping.