A-Nor: New Concepts for the Norbornadiene/Quadricyclane (NBD/QC) Interconversion

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For the design and optimization of future MOST systems, precise chemical fine-tuning as well as comprehensive understanding of the photochemical isomerization mechanism is of major importance. Therefore, the syntheses of new norbornadiene/quadricyclane (NBD/QC) derivatives and the development of efficient and unprecedented catalytically triggered energy release processes is targeted. Based on the NBD/QC interconversion couple, as well as chromophore-mostophore hybrid structures, our goal is to optimize the molecular architectures and system properties in order to approach competitive MOST applications while simultaneously generating new insights into the fundamental mechanistics of the underlying photoisomerization and energy release processes. For this purpose, our proposal will consist of three work-packages. The thrust of work-package 1 is to generate a library of new NBD/QC couples and their related heterocyclic analogues containing e.g. oxygen or nitrogen in the bridge. Consequently, the focus is to perform tailored functionalization of NBD/QC couples to obtain optimized photophysical properties, which are necessary for future applications. The synthesis of novel rylene-norbornadiene hybride structures as model compounds for fully photo-switchable systems is the task of work package 2. This will help to unravel the fundamental switching process and generate comprehensive understanding of the underlying photophysical mechanism, thus allowing for precise chemical tuning of the related properties of NBD/QC couples. In work-package 3, both the [2+2] photocyclization from NBD to QC and the catalytic back-conversion within shell-by-shell functionalized nanoparticles and their confined space in the bilayer, will be investigated. Therefore, tailor-made functionalized nanoparticles will be used as a) quasi-homogeneous catalysts, b) platforms providing a tunable confined space reaction scenario and c) as phase-transfer mediators allowing for example to operate in aqueous solutions. Through the conscientious processing of the proposed work-packages, three main research questions will be investigated: (i) How can we design and optimize NBD/QC couples as suitable MOST systems with low synthetic effort and efficient reaction procedures? (ii) How do we implement the fundamental mechanistic understanding to unravel the key factors limiting the relevant MOST properties such as energy storage density? (iii) How can we maximize the efficiency of the catalytic energy release trigged by tailor-made nanoparticle-based catalysts and what are the main challenges by using such systems for practical applications? As essential part within FOR MOST, our project will push forward the future MOST technology by providing a series of novel norbornadiene-based energy storage systems, model compounds for the investigation of fundamental mechanistics and nanoparticle-based catalysts to trigger the energy release reaction.