Detection of β-transition in polyesters <i>via</i> clusteroluminescence

The secondary transition of polymer chains is crucial for understanding its multiple properties, yet conventional methods to measure the corresponding transition temperature often face limitations in sensitivity and practicality. Fluorescence spectroscopy, renowned for its real-time response, high sensitivity, and non-destructive nature, has emerged as a powerful alternative. However, existing fluorescence-based techniques typically rely on external probes and exhibit limited sensitivity to sub-glass transitions. Herein, we introduce a novel approach leveraging clusteroluminescence (CL), a unique luminescence generated from the through-space interactions between polymer chains, to monitor secondary transitions in polyesters with unprecedented sensitivity. By analyzing the first derivative of fluorescence intensity with respect to temperature, we successfully identify both the glass transition temperature (<i>T</i>_g) and the sub-<i>T</i>_g transition (<i>T</i>_β). This work not only demonstrates the potential of CL as a robust tool for probing polymer dynamics, but also represents the first probe-free method for simultaneously monitoring <i>T</i>_g and <i>T</i>_β transitions. Our findings open up new avenues for advanced material characterization and deepen the understanding of polymer behavior.