Luminescence variation by rigidity control of acrylic composite materials

Photoluminescent composite materials whose emission depends on the rigidity of the hosting matrix were synthesized by dispersing molecular copper iodide clusters, [Cu₄I₄L₄], in a series of photopolymerizable matrices exhibiting different glass transition temperatures (T_g). These matrices were obtained by blending at different molar ratios two chemically similar acrylic monomers presenting different flexibility. The kinetics of the photocuring process was followed by Real Time FTIR and high conversion values were achieved for all the formulations indicating a high degree of polymerization. In addition to the optical properties, the cluster integrity in the materials was demonstrated by an XPS study. The photoluminescence characterization of the composite materials showed a red shift of the emission band by decreasing the T_g value of the polymeric matrix. A change of the emitted color ranging from yellow to orange is thus observed. This effect is based on the luminescence rigidochromism of the copper iodide cluster which emits at lower energy by increasing the medium flexibility. These composite materials make it possible to control selectively the light emission by changing the rigidity of the matrix while keeping the same emitter and are very promising in the field of photoactive materials based on molecular copper iodide clusters.