Light-Induced Thermal and Optical Behavior of Functionalized Side-Chain Push–Pull Azo Polymer Thin Films

Abstract

In this work, we focus on the impact of UV/vis light on the physical properties of polymers with azo chromophores. We study the relationship between light, the structure of azo molecules, and their thermal and optical properties. Our research objects are functionalized side-chain push−pull mono and bis-azo polymer thin films (80−457 nm). We induced structural changes in the azo molecules by photoisomerization (applying light at 405 nm and 300 mW/cm 2 ), and we observed them by measuring the transmittance spectra. We characterized the local thermal conductivity (κ) of azo polymers by scanning thermal microscopy (SThM). We used quantum chemistry calculations to explain the thermal and optical reactions of the azo polymers to illumination by light. We also used photothermal radiometry to support SThM. We imaged the surfaces of azo polymers in their trans and cis states by atomic force microscopy. The SThM measurements show reversible κ changes for the azo polymer with CN groups, between 0.21 and 0.17 W m −1 K −1 for the trans and cis states, respectively.