In-situ NMR spectroscopic investigations of the organic photochromism in spiropyran and spiroxazine norbornens and their homopolymers

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Upon irradiation with ultraviolet light (UV) spiropyranes and -oxazines show a change in color mostly from colorless to purple. This change in color is caused by a reversible ring opening reaction from the closed spiro- to the open merocyanine-form. The changes induced in physical properties, like the dipole moment, are used for the design of stimuli responsive materials. For the development of such materials, parameters like the degree of conversion to the open form upon irradiation or reaction rates of the thermal ring closing reaction are important. Furthermore these properties are related to the conditions present (solvent, temperature, etc.). The open merocyanine is stabilized by polar solvents, e.g., and thus thermal back reaction is slowed down. A goal of the proposed project is the investigation of the organic photochromism of monomeric and polymeric spiropyran and -oxazine-norbornenes with in-situ NMR spectroscopy. The use and development of NMR-spectroscopic methods to investigate organic photochromism is a main objective of the proposed project. Spiropyrans show degradation reactions upon irradiation. A deeper and systematic understanding of the pathways of photodegradation of spiropyran and spiroxazine norbornens is also in the focus of our investigations, as these limit the applicability of such systems. Furthermore the interaction of spiropyrans and -oxazine with (metal) ions is within the scope of this project as such interactions can have an influence on the photochromic behavior of spiropyrans and -oxazines. A deeper knowledge of the scope of these interactions would allow for a targeted use of ions to influence transport properties in mesoporous films. The monomers and polymers are synthesized in the the group of Andrieu-Brunsen and shall be used for the development of photocontrollable ionic transport in mesoporus silica-films. Results obtained from our in-situ NMR investigations of such spiropyrans and -oxazines with respect to photodecomposition reactions can then be used to improve before mentioned hybrid materials.