High refractive index coumarin-based photorefractive polysiloxanes

In the past decades the development of photorefractive devices evolved rapidly as can be seen by the increasing number of publications and numerous applications. There is still need of innovative materials which are suitable for a broad range of applications through tailored properties. We present photorefractive linear and crosslinked polysiloxanes with refractive indices of up to n = 1.603 which may be tuned in their refractive index in a range of up to Δn = 0.04 photochemically. The polysiloxanes, more commonly named silicones, have side chains containing coumarin which are attached to the polymer backbone via different spacers ranging in length from 3 to 9 methyl groups. The coumarins undergo wavelength-dependent photodimerization and photocleavage in the polymer which cause the desired refractive index changes. The polysiloxanes have low glass transition temperatures ranging from −2 °C to 35 °C and show a high thermal stability (T5% > 410 °C). These properties make these materials promising candidates for the manufacture of photo tunable polymers, e.g. for the use as optical data storage materials, alignment of liquid crystals, and photorefractive intraocular lenses.