Magnetic properties of a polyfluorene derivative containing complexed neodymium ions

Abstract

Poly[9,9′‐dihexylfluorene‐2,7‐diyl)‐6,6″‐(2,2′:6′,2″‐terpyridine)] (LaPPS75) and its complexes with neodymium were synthesized and characterized. Magnetic measurements showed that the noncomplexed polymer presented a ferromagnetic contribution due to the formation of π stacking, and that in absence of those, the ferromagnetic behavior is suppressed. The pristine polymer, the complexed one and a low‐molecular‐weight model compound with the same structure of the complexed site in the parent polymer were studied. The observed behavior found is presented and discussed, the most important finding was that when a conjugated chain is used as a host for the metallic ion, an amplification of four times for the magnetization is achieved, using the same metallic content for complexed polymer and model compound for comparison. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 304–311

Magnetic Properties of a Polyfluorene Derivative Metallopolymer Containing Neodymium Ions

“…The polymer (LaPPS59) was prepared through the crosscoupling Suzuki polycondensation and the metallopolymers (LaPPS59Nd / LaPPS59Nd-Cl) were synthesized following reported procedures. [38] A model compound (LaPPS59M) was synthesized to simulate complexed sites as shown in Scheme 1 in Supporting Information.…”

“…When the ion is inserted into a conjugated polymer chain, it suffers the influence of high mobile 𝜋 surrounding electrons. The subject has been addressed recently in the literature, [38] but a definitive explanation of the nature of interactions polymer-ion has yet to be found. The experimental results showed that magnetic properties can be very much altered, not only by the presence of the polymer backbone itself but also by the inter-macromolecular interaction forces.…”

“…Moreover, the more rigid the polymer chain, more prone to the stacking the system is, due to the enhancement of the electronic delocalization. In another contribution, [38] we have used a similar polymer to the one explored in this work, with the difference that here we have used phenanthroline in place of the t-pyridine used previously. The rationale for that is that phenanthroline is a condensed three ring system much more rigid than the t-pyridine, that allows a degree of rotation between its three rings.…”

“…This approach carries an important potential for the obtainment of magnetic properties at ambient temperature, [37] as demonstrated in the results shown here. In a recent publication, [38] we have demonstrated that a conjugated chain, namely Poly[9,9'dihexylfluorene-2,7-diyl)-6,6"-(2,2':6':2"-terpyridine)], (an alternated copolymer of fluorene and terpyridine) complexed with neodymium was able to amplify fourfold the magnetization response of the corresponding low molecular weight material. Thus, these behaviors indicate that the mobile 𝜋 electrons play an important role for the obtainment of magnetic properties in organic solids, which was accounted for the interaction of the mobile electrons of the rare earth metal and the conducting band of the polymer.…”

“…Moreover, it was demonstrated that the intermolecular 𝜋 stacking of the polymer brought about macroscopic effects enhancing furthermore this interaction. [38,39] Considering the consensus that the 𝜋-stacking between the chains enhances the electronic interaction polymer-metal, [38,39] we designed a molecule similar to the previous one by changing the terpyridine moiety by 1,10-phenanthroline. This would impart rigidity and planarity, thus increasing intermolecular association not found in the terpyridine copolymer, because the pyridine rings in this case are able to assume several conformations, thus somehow hampering the intermolecular association.…”