Poly(Phenylene Ethynylene) Based Thermochromic Nanoparticles with Large Fluorescence Shifts for Thermal Sensing

In this study, we developed a poly(phenylene ethynylene) (PPE–CO2)-based nanoparticle thermal sensor with a large spectral shift. The sensor was developed by carefully tuning the ionic strength and the supporting polyvinylpyrrolidone-co-polystyrene (PVP-co-PS) nanoparticles concentration. The nanoparticle thermometer exhibited a linear response between 20 and 90 °C and a large 62.0 nm shift in its maximum emission, from 519.2 to 457.2 nm. This resulted in an excellent absolute thermochromic sensitivity of 0.795 nm/°C, enabled by precise control of nanoscale polymer–nanoparticle interactions that influence emission properties. The sensor demonstrated good reversibility and cyclability when exposed to heating and cooling cycles. In addition to the observed spectral shift, the PPE–CO2/PVP-co-PS nanothermometer also exhibited a lifetime-based thermal response with an absolute sensitivity of 0.024 ns/°C between 20 and 90 °C. Single-particle spectroscopy measurements confirmed changes in PPE–CO2 inter/intrachain exciton coupling when assembled onto the PVP-co-PS nanoparticles in response to temperature variations, providing mechanistic insights into the thermal response of the developed sensor.