Ziyang Liu is a doctoral student at the Graduate School of Frontier Sciences, The University of Tokyo, and currently a research trainee in the Supermolecules Group at the Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS). His research focuses on molecular doping of conjugated polymers, particularly dopant organization, intermolecular interactions, and structure–property relationships in organic semiconductors.

Structural order plays a critical role in charge transport in semicrystalline conjugated polymers, and extensive efforts have therefore focused on controlling polymer-chain packing and crystallinity.[1] Although ion intercalation into crystalline conjugated-polymer films has been demonstrated,[2] the organization and chemical state of dopant ions within the resulting doped films remain comparatively underexplored, despite their direct influence on charge compensation and electronic properties.

Here, we investigate multivalent-anion doping of a semicrystalline polythiophene derivative, aiming to introduce directional intermolecular interactions between dopant species through hydrogen bonding (Fig. 1). Combined UV–vis–NIR and XPS analyses reveal an apparent charge-compensation ratio of approximately 1.3 holes per incorporated dopant molecule, below the two-hole compensation expected for a fully deprotonated divalent anion, suggesting partial protonation of the incorporated dopant. Supporting this interpretation, FTIR spectroscopy reveals proton-associated, hydrogen-bonded O–H species in the doped films. These results indicate that protonation may regulate the effective valency of multivalent dopants, while hydrogen bonding offers a molecular-level strategy for controlling dopant organization in semicrystalline conjugated polymers.

1. I. E. Jacobs et al., J. Am. Chem. Soc. 144, 3005–3019 (2022).
2. M. Ishii et al., Nature 622, 285–291 (2023).