Ionic Tunability of Conjugated Polyelectrolyte Solutions

Abstract

Conjugated polyelectrolytes (CPEs), which combine a π-conjugated polymer backbone with pendant ionic functionalities, offer an opportunity for electrostatic control of materials properties. In this work, the mesoscale morphology and physical properties of a high-mobility conjugated polyelectrolyte are tuned by the addition of salt, variation of the charge-compensating counterion, and complexation with an oppositely charged polyelectrolyte containing the same π-conjugated backbone. In systems with a single polyelectrolyte species, added ions screen the electrostatic repulsions stabilizing the gel-phase, resulting in the dissolution of ionic cross-links and hydrophobic collapse. Exchanging the charge compensating counterion is found to enable finer structural control of the solution behavior and modulation of the self-doping behavior. Finally, novel CPE–CPE complexes resulting in dense solutions and gels of semiconductive material are produced by combination of oppositely charged polyelectrolytes. Such concentrated CPE formulations should be useful materials for mixed electronic–ionic conduction and pseudocapacitative energy storage.

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

“…Fiber formation appears to result from the delicate interplay of short range poor solvent aggregation and longer-range electrostatic repulsion, with the polymer's semiflexibility helping nucleate fiber formation. While the fiber formation in this work is generally consistent with that observed experimentally, 12,14 it is important to note that these experimental systems employ polymers with ∼five times larger polymer persistence lengths, and consequently fiber formation occupies larger length scales and is significantly more pronounced. The molecularly detailed view of semidilute poor solvent CPE morphologies in this work suggests the formation of regularly separated multi-chain fibers at the ∼ 10nm length scale.…”

“…To the author's best knowledge, this is the first assignment of a harmonic peak in a modeled CPE structure factor, providing a potential alternative interpretation of the SANS peaks observed in a similar CPE system. 13,14 Note that when side chain beads are included in the structure factor, the harmonic peak becomes much less distinct (Figure S5).…”

“…or micelles at low concentrations. 10,11 For rigid CPE backbones, these micelles can become effectively crosslinked via poor-solvent interactions, forming hydrogels at concentrations as low as 1% w/v, [12][13][14] with longer chain lengths improving the percolation and electronic conductivity of these networks. 15,16 More flexible CPEs (e.g.…”

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

“…Conjugated polyelectrolytes are a material platform that can support long-range energy transfer and enhanced charge mobility when paired with counterions that induce extended π-delocalization as a result of noncovalent interactions. ,− Electrolytes have been used to process films with ordered microstructures and photovoltaic devices with improved charge transport. ,− Relatively recently, oppositely charged conjugated polyelectrolytes have been paired in solutions to form what are known as conjugated polyelectrolyte complexes (CPECs) and have been investigated for their light-harvesting potential in solutions and other complex environments. ,,− For example, a rudimentary light-harvesting complex has been demonstrated using a polyelectrolyte complex that associates with a membrane and facilitates energy transfer to an acceptor located at the membrane’s interior . Photoinduced charge transfer has also been observed between polyelectrolytes and electrolytic small-molecule acceptors. ,, Charge-transfer behavior has been shown to be sensitive to specifics of polyelectrolyte interactions, , and long-lived charge separation with potential for photoredox chemistry has been demonstrated …”

Ionic Push–Pull Polythiophenes: A Further Step towards Eco-Friendly BHJ Organic Solar Cells

“…Indeed, the presence of ionic groups promotes intermolecular interactions, which should improve the contact between the active layer and the electrode, thus enhancing the efficiency step of extraction of the charge carriers at the interface with the electrodes [ 17 , 18 , 19 ]. However, despite these materials also being used lately as photoactive layers in BHJ cells, the presence of ionic groups may also induce disorder at the macromolecular level in the solid state or act as traps for charges, thus leading to unsatisfactory efficiency values [ 20 , 21 , 22 , 23 ]. Nevertheless, this research field is constantly evolving.…”