1 December 1997 Dynamic dielectric screening and exciton binding energies in conjugated polymers
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Semi-empirical quantum chemistry predicts exciton binding energies for a single chain of a conjugated polymer that are significantly larger than those measured in the solid state. This paper continues our development of an electronic- polaron model that explicitly includes Coulomb screening from adjacent chains. The original model used Huckel theory to describe the polarization induced in the surrounding solvent chains. Here, the use of Pariser-Parr-Pople theory instead of Huckel theory is shown to have little effect on the solvation energies obtained from the electronic-polaron model. The results confirm that the dynamic dielectric response plays a crucial role in establishing the exciton binding energy. The free electron-hole pair states are well solvated because the charge fluctuations arising from electron-hole motion are slow and the polarization of the surrounding chains can nearly follow the electron-hole motion. HOwever, the exciton state is weakly solvated because the charge-fluctuations are fast, and the surrounding chains cannot follow the electron-hole motion. The electron and hole must then shed their solvation cloud when they join to form an exciton. This consequence of dynamic dielectric screening enhances the differential solvation of the free electron-hole pair versus the exciton, and leads to a large reduction in the exciton binding energy.
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Jason Weibel, Jason Weibel, David Yaron, David Yaron, } "Dynamic dielectric screening and exciton binding energies in conjugated polymers", Proc. SPIE 3145, Optical Probes of Conjugated Polymers, (1 December 1997); doi: 10.1117/12.279281; https://doi.org/10.1117/12.279281

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