• Multilayers;
  • Optically active materials;
  • Patterning;
  • Photochemistry;
  • Photoluminescence;
  • Polymers


Novel patternable, light-reflecting multilayer polymer films are presented. The investigated elements comprise 1024 nanolayers of two different, transparent polymers in strictly alternating fashion. Polymers with different refractive indices were employed and the individual layer thickness was controlled between 50 and 200 nm; as a result the investigated films exhibit pronounced optical interference effects. Different photoreactive additives were integrated into the multilayer films, rendering the optical characteristics of these elements tunable. One approach relied on the use of photoreactive blends of poly(methyl methacrylate) (PMMA) and up to 25 wt.-% of trans-cinnamic acid (CA) or trans-methyl cinnamate (MC). Upon exposure to ultraviolet (UV) radiation, CA and MC undergo dimerization through 2+2 cycloaddition, leading to a significant decrease of the blend's refractive index. As a result, the reflectivity of the multilayer films based on these photoreactive blends changes considerably upon photoreaction. The second approach was based on the use of blends of PMMA and 2-(2′-benzoylphenyl)benzoxazole (BzPO), a ‘caged’ photoluminescent dye. This benzoyl ester of 2-(2′-hydroxyphenyl)benzoxazole (HPBO) is not photoluminescent, but upon exposure to appropriate UV radiation, the ester bond is cleaved, and the photoluminescent HPBO is quantitatively restored. Thus, using conventional photolithographic techniques, reflective multilayer films were patterned with photoluminescent designs.