Functional silicon crosslinks in conjugated polymer networks.

Amorphous conjugated polymer networks (CPNs) are highly crosslinked materials based on rigid organic building blocks. The introduction of main group elements not only imparts new properties but also enables new synthetic approaches. While several examples including heteroatoms (e.g. N, O, S) have focused on the structure and morphology, there has been less progress on the preparation of amorphous CPNs based on Group 14 elements (e.g., Si, Ge, Sn). A limitation on the synthesis of Group 14 containing CPNs is the dearth of appropriate crosslinkers. Herein we report a novel disilane (e.g., Si-Si bond) containing crosslinker, which affords examples of Si-Si crosslinked π-conjugated polysilafluorenes with tunable levels of crosslinking. The novel structure and synthetic approach accesses well-defined polymeric materials and we report rigorous characterization by 1H, 13C, and 29Si NMR spectroscopy. Density functional theory was used to study the electronic structure of neutral, cationic, and anionic oligomer models. A decrease in bond dissociation energies of the Si-Si bonds was found after reduction or oxidation, supporting the presence of redox active crosslinks. While previous work has focused on polymerization strategies for incorporating silicon into the main-chain of polymer strands, such as the well-known polysilanes, using Si-Si bonds as crosslinks in macromolecules has remained unstudied.