Dynamic interaction between polarons and torsional vibrations in conjugated polymers

Abstract

ABSTRACT:We propose a model for the electronic interaction associated with torsional and bond length vibrations in quasi-one-dimensional chains of conjugated polymers. The model admits conformational bond length objects like polarons and bipolarons and torsional modes of vibration. It is shown that the dynamics of these objects can be studied by numerically integrating the corresponding time-dependent equations of motion for the bond length; ring torsion angle, and -electrons. An extension of the PPP and SSH models is numerically solved using the time-dependent Hartree-Fock approximation. A wide range of conducting polymers is simulated by varying the moment of inertia of the monomers [ranging from polypyrrole to poly(3-hexyl)thiophene]. The stereometric interactions between chains are parametrically considered with different torsional potentials. The results show that polarons and bipolarons are trapped between the antinodes of torsional vibration modes with wavelengths larger than their widths. This effect damps down their mobility. We also found that torsional vibration modes with very long wavelengths or wavelengths shorter than the width of polarons and bipolarons produce almost no effect on their propagation.

Enhanced Charge Transfer Doping Efficiency in J-Aggregate Poly(3-hexylthiophene) Nanofibers

“…For example, if the injected polymer hole polaron can escape the Coulombic attraction with the ionized dopant, increased free carrier levels and conductivities are observed. Based on our present and previously reported findings, polymer chains with high intrachain order promote exciton and polaron intrachain delocalization which is essential for producing mobile charges and increasing conductivity. Otherwise, conformational and packing disorder (i.e., torsional distortions, packing defects, and ordered–disordered domain boundaries) localizes injected holes leading to bound charge transfer complexes that do not contribute to increased conductivity.…”

2D-IR Studies of Annealing-Induced Changes to Structural Dynamics in Organic Semiconductor Thin Films

“…Using a simplified model that incorporated only torsional degrees of freedom, de Brito and co-workers have shown through simulations that charge carrier trapping occurs along P3HT chains when the antinode spacings of torsional vibrations are comparable to the size of the polaron or bipolaron, whereas vibrational wavelengths significantly larger or smaller than the polaron width have no appreciable effect on its mobility. 77 Therefore, a shift of the low frequency vibrations to higher energies during annealing, characterized as a transition of the 400 fs FCF component to the motionally narrowed regime, could have the effect of boosting mobilities by eliminating hole trapping along the polymer chains.…”

“…Vukmirovic and co-workers have recently used molecular dynamics simulations to demonstrate that charge carriers can in fact be localized through the disordered regions of P3HT by torsional motions, leading to a decrease of charge mobilities. , Our experimental evidence in this work supports the notion that mobility enhancements can originate in both static and dynamic structural changes. Using a simplified model that incorporated only torsional degrees of freedom, de Brito and co-workers have shown through simulations that charge carrier trapping occurs along P3HT chains when the antinode spacings of torsional vibrations are comparable to the size of the polaron or bipolaron, whereas vibrational wavelengths significantly larger or smaller than the polaron width have no appreciable effect on its mobility . Therefore, a shift of the low frequency vibrations to higher energies during annealing, characterized as a transition of the 400 fs FCF component to the motionally narrowed regime, could have the effect of boosting mobilities by eliminating hole trapping along the polymer chains.…”

Polarons in one‐dimensional molecular chains with intermolecular and intramolecular vibrations

“…A considerable number of works have been devoted to the study of the dynamics and thermodynamics 19 of polarons in a large variety of compounds including polymers 9, 10, 13, 20–23, superconducting 24, metallic, semiconducting, insulating 25 as well as magnetic 26–29 materials. Closer to our main topic, polarons have been greatly discussed in connection with the transfer of energy in molecular and biomolecular systems including nanostructured molecular compounds like carbon nanotubes 30 and DNA 31–37.…”