• While it has been known for some time that conjugated polyelectrolytes (CPEs) can assemble with biological macromolecules, leading to a strong optical response due to structural changes in the polymer backbone, we managed to gain unprecedented atomistic-level understanding of how single DNA strands impact the conformation of thiophene-based CPEs, allowing to predict which combinations of DNA sequences with specific CPEs yield the largest photophysical changes.
• The electronic structure and origin of the optical transitions in doped organic semiconductors have recently been put into question by theoretical work. Our excited-state study on a self-doped CPE has allowed first direct experimental evidence for this new interpretation, which radically changes the understanding of the optoelectronics in those doped systems.
• For doped small molecule TAPC, we were able to evidence excited-state charge transfer between cationic TAPC molecules and their neutral neighbors, leading to enhanced conductivity. This brings insight to the debated question of how charges separate from he Coulomb potential of the ionized dopant, highlighting the role of excess energy and delocalization.
• We have put together a unique palette of experiments to gain comprehensive insights to the functioning of organic electrochemical transistors (OECTs). In particular, the development and full characterization of a highly sensitive terahertz (THz) detection scheme represent a significant technological advance, that has allowed us to carry out in-operando THz measurements on OECTs, which has not yet been achieved by any other group.
• By measuring the electrochemical dedoping and redoping dynamics of PEDOT:PSS at different temperatures, we have determined the full thermodynamic reaction profile of the redox reactions in this most used organic bioelectronic material. We revealed that dedoping is driven by enthalpy, while redoping is driven by entropy and that the reaction rates are determined by the transition state entropy.
• We have obtained a full picture of the electrochemical doping of P3HT (a state-of-the-art polymer) in KPF6 electrolyte, using in-operando spectroscopy in different wavelength ranges. We have distinguished the redox species in the ordered and disordered regions of semicrystalline P3HT due to their different optical and Raman signatures. This revealed that bipolarons preferentially form in the disordered regions, which are by themselves not very conductive. Interestingly, these bipolarons still enhance the overall fraction of conductive charge (seen by THz spectroscopy), possibly by helping the transport between ordered regions along tie chains.
• We have applied our experimental approach to a variety of materials, including thiophenes with ioniuc sidechains, glycolated ProDOT derivatives, light-responsive systems, and OECTs interfaced with lipid membranes.
• We have shown by SFG spectroscopy that the alkyl sidechains of P3HT stand up in air but lie down in water, while hydrophillic sidechains also stand up in water, which can impcact ion peneration and interfacial fields.
