Supramolecular Complexes of Conjugated Polyelectrolytes with Poly(ethylene oxide): Multifunctional Luminescent Semiconductors Exhibiting Electronic and Ionic Transport

Abstract

Solution processability endows polymer semiconductors with several intriguing prospects, from low-cost processing, such as inkjet printing, to the possibility of creating new materials by simply mixing solutions. Polymer blends have already been exploited in light-emitting diodes (LEDs) [1] and photovoltaic diodes, [2,3] as well as light-emitting electrochemical cells (LECs), [4] although the factors controlling their supramolecular structures [5] and properties are not fully understood. Most polymer blends undergo phase segregation. [6] This has been used to generate large-area heterojunctions, [2] but it can be detrimental where solid solutions are sought to increase photoluminescence (PL) efficiency, and where rough surface morphology is a problem. Here we use three supramolecular strategies to prepare a complex material that has none of these drawbacks and benefits from enhanced electroluminescence properties: firstly, ionic interactions favor mixing of a conjugated polyelectrolyte with poly(ethylene oxide), PEO, preventing phase segregation and boosting the PL efficiency; secondly, the PEO facilitates ion transport and allows fabrication of LEC-like devices which display a two orders-of-magnitude increase in the electroluminescence (EL) efficiency; thirdly, threading the conjugated polymer through cyclodextrins gives higher PL efficiencies at small PEO loadings, and increases the EL efficiency over the full range of PEO concentrations. Insulated molecular wires, IMWs, consisting of conjugated polymers threaded through cyclodextrin rings (b-CD-poly(paraphenylene) (b-CD-PPP), b-CD-poly(fluorene) (b-CD-PF), a-CD-poly(4,4′-diphenylene vinylene) (a-CD-PDV), and b-CD-poly(4,4′-diphenylene vinylene) (b-CD-PDV); Fig. 1) are versatile supramolecular architectures [7] that display a reduced degree of interchain interactions reflected in higher electroluminescence efficiency, blue-shifted absorption/emission, and reduced luminescence quenching and packing density, when compared to their uninsulated analogues (PPP, PDV, and PF). [8] In this paper we exploit their polyelectrolytic nature, and use the presence of lithium carboxylate and sulfonate substituents to drive the formation of supramolecular complexes with polymers featuring ion-coordination properties. This supramolecular assembly enables us to reduce the tendency of the different components to phase separate, to promote smooth surface morphologies, and to boost the PL and EL efficiency. The interaction of PEO with polyrotaxanes in aqueous solution was tested by fluorescence titration, using b-CD-PDV and PDV. This experiment revealed that both conjugated polymers bind PEO strongly even under extremely dilute conditions (1 ppm PEO by weight, ca. 1 × 10 -8 mol dm -3 of both components). The fluorescence spectra of PDV at a range of PEO concentrations are shown in Figure 2a, and the corresponding titration curve is plotted in Figure 2b (see Fig. S1 in the Supporting Information for analogous data for b-CD-PDV). The titration curves for b-CD-PDV and PDV fit remark...

Control of Rapid Formation of Interchain Excited States in Sugar‐Threaded Supramolecular Wires

“…However, here we show that polyrotaxane photoluminescence decay dynamics are exponential and independent of concentration despite the incomplete shielding of the conjugated cores by the cyclodextrins. [8,16] Our results demonstrate that supramolecular encapsulation is an extremely effective and versatile strategy to control the photophysics of semiconducting polymers and is thus crucial to the development of organic electronics. Control of the dimensionality of excited states in electronic and photonic materials has been proposed as an effective tool for tailoring their photophysics.…”

“…Previous investigations in the solid state have shown that polyrotaxanes benefit from a partial reduction of interchain electronic interactions, evident from an increase in luminescence efficiency, and a blue-shifted emission. [8,16,19] Incorporation of the threaded b-cyclodextrin macrocycles also reduces energy transport rates and therefore exciton diffusion to sites that quench [20,21] or red-shift the luminescence. [6] Such properties are all crucially relevant to the development of conjugated semiconductors for optoelectronics applications.…”

Isolierte molekulare Drähte

“…d) Veränderung der Elektrolumineszenzeffizienz mit dem PEOGewichtsanteil für Mischungen mit PDV1&a-CD, PDV1&b-CD und PDV1. [190] Feld wandern Elektronen und Defektelektronen durch das Material, bevor sie schließlich kombinieren und angeregte Zustände erzeugen, die daraufhin fluoreszieren.…”

“…[190] Die EL-Quantenausbeuten der freien Polymere werden durch Mischen mit PEO ebenfalls gesteigert, sie bleiben jedoch deutlich hinter den Werten für die Polyrotaxane zurück (siehe die logarithmische Auftragung in Abbildung 26 d). Fluoreszenztitrationen in verdünnten wässrigen Lösungen und AFM-Untersuchungen sprechen für eine starke Bindung von PEO an diese Polyrotaxane, die wohl auf der Komplexierung der Lithiumkationen beruht.…”

Poly-and oligothiophenes : Optical probes for multimodal fluorescent assessment of biological processes

“…The charges also provide for interactions with ionic species. Another advantage is their amphiphilic character; due to the hydrophobic backbone and the hydrophilic side-chains, CPEs are able to aggregate in aqueous solutions and some CPEs can form supramolecular complexes [28]. This amphiphilic character allows for both electrostatic and hydrophobic interactions with different analytes.…”