Photoinduced refractive index changes of 3-phenyl-coumarin containing polymers for ophthalmic applications

• Photorefractive acrylic polymer with phenylcoumarin in the side chain.
• High refractive index of n = 1.61.
• Light-induced refractive index change of Δn = 0.045.
• High lightfastness of the polymer.
• Refractive index change due to light-triggered cyclobutan cleavage.

A novel photorefractive polymer has been developed where 3-phenyl-coumarin (3PC) is attached via alkyl spacers to a methacrylate backbone. The 3PC is a fusion of the structural motives of coumarin and stilbene. In 3PC the E/Z  -isomerization, known from stilbenes, is blocked and a more extended conjugated π-electron system than in coumarin is obtained. A methacrylate based polymeric material comprising 3PC in the side chain has been synthesized and its photorefractive properties have been studied. The initial refractive index is n633o = 1.613 and the maximal light-induced change of the refractive index was found to be Δn633 = −0.045 in spin-coated thin films as well as in bulk material. The glass transition temperature of about 37 °C and the high lightfastness of the polymer make it a candidate material for intraocular lenses with photo-tunable refractive index properties.

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