Photochromic spiropyran- and spirooxazine-homopolymers in mesoporous thin films by surface initiated ROMP

The control of ionic permselectivity in porous films is an interesting aspect in the context of lab-on-chip devices and μ-electronics. Especially, visible light triggered ionic permselectivity control is of relevance because control by light can be maintained externally without changing internal system parameters. In addition, light is a sustainable energy source if sunlight is used. Here, we present the first mesoporous films modified with two different photochromic homopolymers by surface-initiated ring opening metathesis polymerization (SI-ROMP). Spiropyran- and spirooxazine functionalized norbornene monomers and the corresponding ROMP homopolymers are synthesized in solution and in mesopores and compared concerning their optical properties such as photochromic conversion kinetics, photostability, and the ratio of converted molecules. Optical properties are investigated using UV/VIS spectroscopy and 1 H-NMR spectroscopy. Especially, spirooxazine, whose surface functionalization has not been studied in detail, shows fast switching properties and higher ratios of photochromically interconverted molecules. After grafting spiropyran- and spirooxazine norbornene homopolymers into mesopores, a slightly faster photochromic interconversion of polymers located inside the mesopores is observed compared to the solution polymers. A strategy towards photochromic SI-ROMP homopolymers based on spiropyran and spirooxazine in mesopores is presented and photochromism is systematically investigated using UV-VIS spectroscopy and NMR.