Complexation of a Conjugated Polyelectrolyte and Impact on Optoelectronic Properties

Abstract

Electrostatic assembly of conjugated polyelectrolytes, which combine a π-conjugated polymer backbone with pendant ionic groups, offer an opportunity for tuning materials properties and a new route for formulating concentrated inks for printable electronics. Complex coacervation, a liquid–liquid phase separation upon complexation of oppositely charged polyelectrolytes in solution, is used to form dense suspensions of π-conjugated material. A model system of a cationic conjugated polyelectrolyte poly­(3-[6′-{N-butylimidazolium}­hexyl]­thiophene) bromide and sodium poly­(styrenesulfonate) dissolved in tetrahydrofuran–water mixtures was used to investigate this complexation behavior of conjugated polyelectrolytes in terms of electrostatic strength, solvent quality, and polymer concentration. The balance of electrostatic interaction between the oppositely charged polyelectrolytes together with their charge compensating counterions and solvent quality for the hydrophobic π-conjugated backbone leads to a rich phase diagram of soluble complexes, precipitates, and complex coacervates. The conjugated polyelectrolyte in the polyelectrolyte complexes has an increased π-conjugation length and enhanced emissivity, with ideal chain configurations due to the reduction of kink sites and torsional disorder. The advantageous photophysical properties in the dense liquid phases makes the scheme attractive for the large-scale processing of optoelectronic devices, chemical sensors, and bioelectronics components.

Li+ and Oxidant Addition To Control Ionic and Electronic Conduction in Ionic Liquid-Functionalized Conjugated Polymers

“…Poly[3-(6'-bromohexyl)thiophene] (P3BrHT) was synthesized according to previous literature. 61,62 An oven-dried Schlenk flask containing 2,5 dibromo-3-(6-bromohexyl)thiophene was placed under vacuum for 2 hours. Dry, degassed THF was added via syringe and the mixture was sparged with Nitrogen.…”

“…59,60 Large, polarizable ionic side-chain moieties serve to weaken ionic associations and increase ion dynamics without the presence of solvent, while the conjugated backbone imparts electron conductivity. 61,62 Polythiophenes with imidazolium side chains have shown intrinsic ionic conductivity up to 10 -4 S cm -1 in the neat state, while also showing evidence of significant long-range order in scattering studies. 60,63 While Ionic liquid functionalized conjugated polymers show potential as solvent-free mixed ion and electron conductors, to this point there have been few studies that investigate lithium-ion conduction in ionic liquid functionalized conjugated polymers.…”

Recent progress in the science of complex coacervation

“…Work by Danielsen et al demonstrated the ability to form liquid coacervates through the use of cosolvent mixtures. 278 Beyond the novelty of invoking π-π interactions, coacervates of conjugated polymers are particularly interesting because of their optical properties. In particular, the formation of a polyelectrolyte com-plex has been shown to result in an increased π-conjugation length, enhanced emissivity, and a dramatically increased fluorescence quantum yield.…”

Small ion effects on self-coacervation phenomena in block polyampholytes

“…This is particularly important as the dilute branch is ignored or constrained to have zero polymer in most theories and simulations of coacervation; yet, the dilute branch is important for both fundamental studies and industrial applications as coacervates are often prepared by entering the phase coexistence window from dilute conditions. 20,22 A single valence of small ions is chosen rather than the total salt concentration (ρs) or the ionic strength, I = ∑ i=± q 2 i ρi to highlight the importance of charge neutrality and partitioning with asymmetries, discussed in Secs. III C-III E. Counter-ions of the polyampholyte are included in ρs (and thus in the ρs,− axis).…”

“…Both simple and complex coacervates, ubiquitous throughout nature from membraneless organelles [1][2][3][4][5][6][7][8][9][10][11] to the wet-adhesion [12][13][14] of mussels and sandcastle worms, have found numerous applications in the food industry, [15][16][17] drug delivery, [18][19][20][21] and organic electronics. 22 Simple, single-component, or self-coacervation of polyampholytes and complex coacervation in the case of mixtures of oppositely charged polyelectrolytes arise from liquid-liquid phase separations that produce a polymer-rich coacervate in coexistence with a polymer-depleted supernatant comprised of primarily salt ions in solution. The broad interest in applications and their fundamental polymer physics has spurred parameterization of their structures and phase diagrams [23][24][25][26][27][28][29][30][31] as well as numerous theories for predicting the richness of coacervation phenomena.…”