Luminescence thermochromism of acrylic materials incorporating copper iodide clusters

Abstract

By incorporating molecular copper iodide clusters of formula [Cu₄I₄L₄] (L = PPh₂(CH₂)₂CH₃) into an UV-polymerizable acrylic resin, namely BEDA (Bisphenol-a-EthoxylateDiAcrylate), transparent and highly emitting photoluminescent composite materials have been synthesized. In these materials, the original luminescence properties of the copper iodide cluster and the transparency and processability of the acrylic matrix are combined. Study of the photopolymerization kinetics shows that the clusters incorporated in low concentration have limited influence on the polymerization reaction leading to a highly cross-linking polymeric matrix. These composite materials exhibit thermochromic luminescence properties with intense emissions varying with the temperature. A perfectly controlled luminescence thermochromism is observed due to a ‘protecting effect’ of the matrix preventing the non-radiative phenomenon of the cluster luminescence. The patterning of these UV-polymerizable photoluminescent films has been also realized by the UV-NIL technique to optimize the light-emitting properties of these materials. The surface patterning acts as a diffraction grating to extract the light which was previously guided inside the film. Moreover, the nanopatterning allows tuning of the emission color of the film as a function of the viewing angle. These composite materials present potential applications as photoactive systems with emission wavelength sensitive to the temperature and the surface nanostructuration.