Control of Photoinduced Charge Separation in Conjugated Polyelectrolyte Complexes through Microstructure-Dependent Exciton Delocalization

Conjugated polyelectrolyte complexes (CPECs) are promising aqueous-compatible materials for artificial light-harvesting applications that possess continuous one-dimensional pathways for exciton and charge delocalization and migration. We demonstrate how donor-acceptor composition in complexes of electrolytic polythiophene (PTAK) and naphthalene diimide (ENDI) impacts the microstructure of the polymer and donor-acceptor interaction, with consequences for photoinduced charge-pair formation and recombination. PTAK evolves from microstructures with H-like to random-coil to J-like excitonic coupling character with increasing ENDI/PTAK charge ratio, while ENDI exhibits weak J-like coupling at high acceptor densities that reflects ordering along PTAK strands. We observe sub-100-fs charge separation between PTAK and ENDI that implies close donor-acceptor orbital proximity and hot-exciton relaxation via charge-transfer exciton states. Multiphasic recombination is observed and reflects a distribution of charge-pair separation distances that is correlated with degree of exciton delocalization, which can be controlled with CPEC composition. Recombination timescales and the fraction of long-lived charge pairs increase with higher excitation energies, consistent with energy-dependent coupling between hot polymer and delocalized charge-transfer excitons. These results indicate that CPEC structure is characterized by an ordered donor-acceptor interface that could be used to induce long-range charge separation for the benefit of applications in artificial light harvesting and photosynthesis.

Automated summary

This study focuses on the impact of donor-acceptor composition in conjugated polyelectrolyte complexes on polymer microstructure and photoinduced charge-pair formation. It demonstrates the relationship between charge separation and recombination processes, as well as the correlation between charge-pair separation distances distribution and exciton delocalization. The results suggest that the ordered donor-acceptor interface in CPECs could be utilized for inducing long-range charge separation in artificial light harvesting and photosynthesis applications.