Electron and Ion Transport in Semi-Dilute Conjugated Polyelectrolytes: View from a Quantum-Mechanically Informed Coarse-Grained Model

Abstract

Conjugated polyelectrolytes (CPEs) are a rising class of organic mixed ionic-electronic conductors, with applications in bio-interfacing electronics and energy harvesting and storage devices. Here, we employ a quantum mechanically informed coarse-grained model coupled with semiclassical rate theory to generate a first view of semidilute CPE morphologies and their corresponding ionic and electronic transport properties. We observe that the poor solvent quality of CPE backbones drives the formation of electrostatically repulsive fibers capable of forming percolating networks at semi- dilute concentrations. The thickness of the fibers and the degree of network connectivity are found to strongly influence the electronic mobilities of the morphologies. Calculated structure factors reveal that fiber formation alters the position and scaling of the inter-chain PE peak relative to good solvent predictions and induces a narrower distribution of interchain spacings. We also observe that electrostatic interactions play a significant role in determining CPE morphology, but have only a small impact on the local site energetics. This work presents a significant step forward in the ability to predict CPE morphology and ion-electron transport properties, and provides insights into how morphology influences electronic and ionic transport in conjugated materials.

Bringing Quantum Mechanics to Coarse-Grained Soft Materials Modeling

“…With the capability of predicting configurationally dependent electronic properties at the CG resolution using ECG, there is significant promise for integrating existing ECG models with established CG simulation capabilities to explore the structure–processing–function relationships of OSCs with unprecedented scalability. Our group − along with others − have pioneered the use of anisotropic CG models that capture the multiscale morphologies of OSCs spanning π-stacking to domain formation. Since anisotropic π-conjugated features (π-stacking and inter-ring dihedral) are preserved at the CG resolution, the morphological dependence on their electronic properties can be systematically investigated by employing phenomenological analysis or TB Hamiltonians without implementing the backmapping process.…”

“…Recently, we have advanced this new paradigm of purely CG structural and electronic prediction models in OSCs to understand the behavior of OSCs in ionic media relevant to biosensing, bioelectronics, and neuromorphic devices. , In this work, thiophene-based conjugated polyelectrolytes were represented using the aforementioned anisotropic CG model, and single-chain conformations were modeled as a function of the solvent, represented by both the solvent dielectric and solvent quality. A phenomenological Hamiltonian in which the electronic couplings were parametrized by the inter-ring dihedrals and nonbonded monomer orientations was then coupled to the sampled configurations to qualitatively address the correlation between chain conformations and charge transport properties. − Importantly, electrostatic potentials resulting from the ionic environment were directly incorporated into modulations in the electronic structure of the Hamiltonian to assess the impact of the electrostatic environment on the electronic wave function, which has never been attempted at these length scales for OSCs.…”