Full Quantification of the Light-Mediated Gilch Polymerization

Abstract

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.

LED‐Illuminated NMR Spectroscopy: A Practical Tool for Mechanistic Studies of Photochemical Reactions

“…Comparable on‐off experiments were also performed to investigate the photochemically induced Gilch polymerization towards a PPV (Scheme ) . It was demonstrated that the polymerization can be initiated by a short light exposure phase and then the polymerization continues in the dark (Figure ), even below the temperature at which thermal initiation/polymerization takes place.…”

Green and stable processing of organic light-emitting diodes from aqueous nanodispersions

“…The fact that we have gained ample experience with PPV chemistry, 21,22 and PLEDs based on PPVs and their blends with other polymers, 17,23,24 allows for optimal performance assessment and optimization protocols amenable to future application of more recent and better performing polymers. The blending with polystyrene is performed for reasons of processability: we anticipate that polystyrene acts as a binder, exhibiting modest flow once heated above its glass transition temperature, thereby closing possible cracks left in the nanoparticle films after wet processing.…”

Unraveling the Photophysical Characteristics, Aromaticity, and Stability of π–Extended Acene‐Quinodimethyl Thioamides†

“…Nevertheless, despite the chimeric nature and attractive chemo‐physical properties of the QDM compounds, many research groups have prepared tens of QDM derivatives [7–11] exhibiting various degrees of stability under ambient conditions. As a result, QDM‐based molecular systems have been useful in applications that range from spintronics [12,13] and optoelectronics devices [14–17] . The diradicaloid species of QDM could be obtained upon photoexcitation, but these species may become relatively unstable under ambient conditions.…”

“…As a result, QDM-based molecular systems have been useful in applications that range from spintronics [12,13] and optoelectronics devices. [14][15][16][17] The diradicaloid species of QDM could be obtained upon photoexcitation, but these species may become relatively unstable under ambient conditions.…”