Photochromism of Azopyridine Side Chain Polymer Controlled by Supramolecular Self-Assembly

Abstract

Polymethacrylate bearing azopyridine side chains was prepared by the radical polymerization of the corresponding methacrylate monomer. The trans-cis photoisomerization of the azopyridine moieties was studied by UV/Vis spectroscopy in both the solution and solid thin film states. The parent polymethacrylate displayed a slightly better photochromic behavior in the THF solution than in the thin film state. This difference became significant when the supramolecular assemblies, based on the hydrogen-bond between the pyridine moieties of the polymer side chain and carboxylic acids of the guest molecule, were formed. Thus, the supramolecular polymer showed a dramatically reduced trans-cis photoisomerization in the thin film state, probably due to the immobilized trans-azopyridine moieties in the confined polymer crystalline environment in terms of the hydrogen bonds. The highly crystalline features of the aliphatic side chains of the guest molecule were demonstrated by the DSC thermograms and polarized optical microscopic images. A better understanding of the photochromism and weak intermolecular interactions of the azopyridine moiety is very important when designing novel functional supramolecular polymers.