The Gilch polymerization is one of the most popular routes toward high molecular weight alkoxy-substituted poly(p-phenylenevinylenes) (PPV) applied in, for instance, organic electronics and bioimaging. As the interplay between optoelectronic performance and (synthesis-related) defects represents an active area of research, control over the polymerization is of utmost importance. In this work we quantify for the first time the rate constants of the reaction steps of the Gilch polymerization. We obtain these values by fitting concentration transients of various key intermediates, measured by in situ low-temperature (−68 °C) 1 H NMR spectroscopy, to kinetic models based on sets of coupled rate equations. The modeling not only accounts for the usual processes of initiation, propagation, transfer, and radical recombination but also involves the side reaction cascade associated with the presence of residual water in the reaction mixture. The results demonstrate that chain growth initiation by active monomer dimerization is slow and rate determining. We show that a low temperature suppresses the occurrence of bisbenzyl and bisbromobenzyl coupling defects. The initiation rate is reduced by orders of magnitude compared to the propagation rate. Hence, fast chain growth occurs at a relative low concentration of radical intermediates, which suppresses defect formation due to both active monomer dimerization and radical−radical recombination.
We show that the exciton transport and decay processes in two poly(p-phenylene vinylene) (PPV) based semiconducting polymers exhibit distinct temperature dependence based on the energetic disorder of the polymer.
Alkoxy-substituted poly(p-phenylenevinylenes) (PPVs) continue to be major workhorse materials in optoelectronics, ranging from thin film electronics to bioimaging. An attractive synthetic route toward PPVs is the Gilch polymerization. Nevertheless, obtaining control over molecular weight and chain constitution is challenging due to the free-radical nature of this reaction. In this work we quantitatively show with in situ UV-irradiation NMR spectroscopy how control over the Gilch polymerization can be enhanced by irradiation with UV-light. The potential of this method has been demonstrated but never interpreted within a quantitative framework, resulting in a lack of mechanistic and kinetic insight. We account for this not only by in situ analyzing and modeling the photochemical Gilch polymerization but also by characterizing the photolysis of the starting material. The latter shows that the solvent THF likely acts as radical transfer agent in the Gilch pathway and similar precursor-based biradical routes. We perform two photopolymerization runs: (i) under continuous UV-irradiation and (ii) by applying a short UV pulse while monitoring the chemical response of the mixture. Since existing models of the Gilch polymerization are inadequate for describing the recorded time−concentration profiles, we develop a new model that couples thermal and photoinduced polymerization. Numerical curve fitting quantifies the rate constants associated with both pathways. We demonstrate that (i) a photoactivated p-quinodimethane species Q* reacts in the (re)initiation and propagation steps, (ii) photopropagation is significantly faster than photoinitiation, and (iii) the photochemical reactions are considerably faster than their thermal analogues, which allows for decoupling the thermal and photochemical pathways at temperatures low enough to suppress the former.
Organische Leuchtdioden (OLEDs) sind moderne Leuchtmittel der nächsten Generation. Sie verwenden (u. a.) halbleitende Polymere für die Lichtemission und erschließen völlig neuartige Anwendungsgebiete wie flexible oder transparente Displays und Leuchten. Für die Implementation von OLEDs in den Chemieunterricht wurden bereits low‐cost Experimente und Lehr‐Lern‐Materialien bereitgestellt. Dieser Beitrag erweitert das Thema um die Synthese eines Halbleiterpolymers im Schulversuch und präsentiert ein gelungenes Beispiel für die curriculare Innovation durch die Kooperation zwischen der Fachdidaktik und Fachwissenschaft.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.