TetraClick - Tetrazines as versatile building blocks in polymer chemistry

The proposed research project is intended to investigate the scope of electron-deficient tetrazine monomers. These materials are expected to be highly interesting building blocks in polymer chemistry which will a) show high reactivity in inverse-electron demand Diels-Alder reactions and b) allow for low-bandgap conjugated polymers. Thus, novel copolymers with unique properties can be achieved. The inverse electron-demand Diels-Alder reaction has only recently gained attention in the polymer science community although it represents an efficient way to combine different polymer chains to yield block copolymers with exciting new properties. One key hypothesis within the proposed research is that this click reaction is orthogonal to two already well-established reactions (azide-alkyne and thiol-ene click chemistry) meaning that under mild, biocompatible conditions, all three click chemistries can be selectively accessed without the need for protecting groups. First indications for this orthogonality are given by results from our preliminary experiments. The electron-deficient nature of the targeted tetrazine structures, which is the leitmotif for enhanced reactivity in the ied-DA reaction, also renders them as useful alternative to electron-deficient monomers for conjugated donor-acceptor polymers. Therefore, as a second major part, tetrazine-containing electroactive copolymers will be investigated. Due to their tuneable electron-deficient nature, the developed tetrazines are expected to act as acceptors in donor-acceptor conjugated polymers and could therefore, in combination with the right electron-rich partner, lead to alternative low-bandgap p-type donor polymers with interesting properties for photovoltaic applications. An important feature of these materials is again the clickability which could be used for morphology stabilisation of bulk heterojunction photovoltaic devices. For this part of the project, collaboration with Professor Ian McCulloch (Imperial College London) is envisaged. Recently his group has been especially active in the development of novel electron-rich structures for electroactive polymers and DFT (density functional theory) studies to optimise the structure of such materials. In summary, this project is seen by the applicants as an opportunity to develop the fundamental knowledge which is needed for development of tetrazine-based materials which can be used in various applications.