Structure-dependent thermochromism of PAZO thin films: theory and experiment

Poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) exhibits a range of unique physical properties that are critical for its diverse applications in photonics, optoelectronics, memory devices, and sensing technologies. In this study, we investigate the thermochromic behavior of PAZO thin films, focusing on the relationship between the structural organization of the polymer side chains and temperature-induced optical changes. By combining experimental spectroscopic techniques with theoretical modeling, we demonstrate that the thermochromic response of PAZO films is strongly influenced by molecular aggregation, film thickness, and thermal treatment conditions. The observed changes in optical properties suggest that this response is governed by temperature-induced modulation of molecular ordering and aggregation state, which in turn alters the electronic transitions responsible for light absorption. Theoretical calculations further support these findings, indicating that temperature-dependent intermolecular interactions and conformational changes play a significant role in shaping the optical behavior of the films. These results provide new insights into the structure–property relationships underlying thermochromism in azopolymer thin films and offer valuable guidelines for the design of thermally responsive photonic materials.