Conjugated Polyelectrolyte-Based Temperature Memory Probes for Applications at the Macro- and Nano-scale Levels

Abstract

Temperature memory probes have the potential to be indispensable in basic science research for their ability to couple temperature measurements with other techniques, both on the macro and nanoscale levels. Herein, we report the development of a fluorescent material with temperature memory properties. Unlike previously developed systems which can only report on a single triggering memory point, the conjugated polyelectrolyte-based sensor detects its exposure to a wide range of temperatures. To achieve this unique property, large poly (phenyl ethylene) (PPE-CO2) conjugated polyelectrolytes are destabilized and locked in a more emissive configuration using a large amphiphilic polymer (polyvinylpyrrolidone PVP) when exposed to heating. With the decrease in solution temperature, the large PVP polymer hinders the aggregation of the stiff and bulky PPE-CO2 back to its original conformation leading to a weaker intramolecular stacked structure with a significantly enhanced radiative emission decay. The temperature memory effect increased with the PVP molecular weight and concentration and was independent of the solution viscosity. The temperature memory effect was tested between 30 C and 70 C and it was retained for at least 24 hours.

As a proof of concept, magnetic nanoparticles were heated using an alternating magnetic field in the presence of the PPE-CO2/PVP sensor. These thermal measurements are often challenging due to the interference of the alternating magnetic field with traditional temperature probes. The fluorescent signal measured 45 minutes after the experiment was able to accurately report back on the maximum temperature solution achieved during the heating experiment.

The system was then studied with different polymers in order to gain further insight on the type of interactions between PPE-CO2-108 and the added polymer. We concluded that the interaction between the former and PVP is nuanced and very specific as only PVP-VA, out of all tested polymers, was able to convey a similar fluorescent behavior with temperature memory properties. Further experimentation must be done for better insight.