Fluorescent-Based Temperature Memory Reporter for Nanoscale Thermal Measurements

Abstract

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 and 70 °C, and it was retained for at least 24 h. 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 min after the experiment was able to accurately report back on the maximum temperature solution achieved during the heating experiment. © 2022 American Chemical Society.