Exciton and polaron interactions in self-assembled conjugated polymer aggregates

John K. Grey; Alan K. Thomas; Jian Gao

doi:10.1117/12.2190229

20 August 2015 Exciton and polaron interactions in self-assembled conjugated polymer aggregates

John K. Grey, Alan K. Thomas, Jian Gao

Proceedings Volume 9549, Physical Chemistry of Interfaces and Nanomaterials XIV; 95490V (2015) https://doi.org/10.1117/12.2190229
Event: SPIE Nanoscience + Engineering, 2015, San Diego, California, United States

Abstract

We study exciton coupling and interconversion between neutral and charged states of different spin in pi-stacked conjugated polymer aggregates. Rigorous self-assembly approaches are used to prepare aggregate nanofibers that permit reliable control of polymer chain conformational and packing (intra- and interchain) order within these structures. Exciton coupling can be tuned between the H- and J-aggregate limits, which has important implications for determining the fates of excitons and polarons. Single molecule intensity modulation spectroscopy was performed on individual nanofibers and large quenching depths of emissive singlet excitons by triplets are found in J-aggregate type structures. We propose that high intrachain order leads to exciton delocalization that effectively lowers singlet-triplet energy splittings thus increasing triplet yields. Exciton-polaron and polaron-polaron interactions are next investigated in both H- and J-type nanofibers where polarons are injected by charge transfer doping. We find that the enhanced intrachain order of J-aggregates enables efficient intrachain polaron transport and leads to significantly larger doping efficiencies than less ordered H-aggregates. As polaron densities increase, signatures of spin-spin interactions between polarons on adjacent chains become appreciable leading to the formation of a spinless bipolaron. Overall, these studies demonstrate the potential for controlling and directing exciton and polaron interactions via tuning of subtle intra- and interchain ordering characteristics of aggregates, which could benefit various polymeric optoelectronic applications.

Conference Presentation

Citation Download Citation

John K. Grey, Alan K. Thomas, and Jian Gao "Exciton and polaron interactions in self-assembled conjugated polymer aggregates", Proc. SPIE 9549, Physical Chemistry of Interfaces and Nanomaterials XIV, 95490V (20 August 2015); https://doi.org/10.1117/12.2190229

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