Electron Transfer in Conjugated Polymer Electrolyte Complexes: Impact of Donor-Acceptor Interactions on Microstructure, Charge Separation, and Charge Recombination

Conjugated polyelectrolyte complexes (CPECs) are an artificial light-harvesting platform formed by pairing oppositely charged conjugated polyelectrolytes in solution. We demonstrate that selective pairing of poly[3-(potassium-4-alkanoate)thiophene-2,5-diyl] (PTAK) of various regioregularity and side-chain lengths with either methyl viologen or an electrolytic naphthalene diimide electron acceptor supports different PTAK microstructures based on specific donor-acceptor stacking relationships. Alteration in microstructure is signaled by distinct signatures of excitonic coupling in steady-state absorption spectra. More ordered PTAK microstructures are obtained in CPECs formed with regioregular PTAK and when the distance between charged groups on the acceptor and PTAK matches. Photoinduced dynamics in these CPECs are characterized by sub-100-fs PTAK-to-acceptor electron transfer with polaron-pair generation in PTAK quenched in higher-order complexes. Rates of subsequent multiphasic charge recombination on picosecond-to-nanosecond timescales are determined by structural characteristics associated with specific donor- acceptor pairings and acceptor-dependent driving force for recombination, with longer-lived charge pairs observed in highly ordered CPEC microstructures. CPECs also demonstrate structure-dependent sensitivity to excitation energy and intensity; excitation energies significantly exceeding PTAK band energy increase exciton delocalization, particularly in complexes with higher structural order. The structure dependence of charge-transfer behaviors in CPECs provides insights for inducing long-range charge separation in related materials for light-harvesting applications.

Automated summary

Conjugated polyelectrolyte complexes (CPECs) are an artificial light-harvesting platform formed by pairing oppositely charged conjugated polyelectrolytes in solution. This study demonstrates the selective pairing and photoinduced dynamics characteristics of different PTAK microstructures, providing insights for inducing long-range charge separation in related materials for light-harvesting applications.