A Modular Cascade Synthetic Strategy Toward Structurally Constrained Boron-doped Polycyclic Aromatic Hydrocarbons

Boron incorporation has attracted great interest in the last decade due to its excellent ability to modify the optoelectronic properties of PAHs, e.g., to provide the resulting systems with intense luminescence, high electron deficiency, strong Lewis acidity, and bestowing the resultant compounds with unique supramolecular behavior. Compared with the benchtop-stable boron doped PAHs (B-PAHs) obtained by applying electronic/kinetic stabilization approach, structurally constrained B-PAHs (sc-B-PAHs) stabilized by chelating effect are expected to enable tight intermolecular packing and enhance the intermolecular interaction in the solid state, therefore improving the charge carrier transport properties. Moreover, sc-B-PAHs are capable of forming Lewis acid-base complexes which can undergo photodissociation in the excited state, giving a dual fluorescence emission. Nevertheless, the related studies on sc-B-PAHs are relatively rare due to the limited synthetic approaches.

The researchers from the group of Prof. Xinliang Feng recently developed a novel synthetic strategy for the construction of difficult-to-access sc-B-PAHs via a cascade reaction from the readily available ortho-aryl-substituted diarylalkynes. This domino process features simplicity and a broad substrate scope. Not only sc-B-PAHs with B-doped [4]helicene structure but also specific BN-doped [4]helicene/double-[4]helicene can be constructed by this approach. Noteworthily, the resultant BN-doped [4]helicene demonstrate distinct supramolecular behavior in the solid state, e.g. mono [4]helicene 1o forms a unique π-stacked dimer and adopts helical columnar stacking, while double [4]helicene 1u establishes an unprecedented π-stacked trimeric structure with a 2D lamellar π-stacking. The presented strategy thus provides a new pathway for the development of novel sc-B-PAHs and expanded B-doped graphene nanostructures.

Reference: Jin-Jiang Zhang, Lin Yang, Fupin Liu, Yubin Fu, Junzhi Liu, Alexey A. Popov, Ji Ma, Xinliang Feng. A Modular Cascade Synthetic Strategy Toward Structurally Constrained Boron-doped Polycyclic Aromatic Hydrocarbons. Angew. Chem. Int. Ed. 2021, https://onlinelibrary.wiley.com/doi/10.1002/anie.202109840.

Acknowledgments: This research was financially supported by the EU Graphene Flagship (Graphene Core 3, 881603), ERC Consolidator Grant (T2DCP, 819698), the Center for Advancing Electronics Dresden (cfaed) and DFG-NSFC Joint Sino-German Research Project (EnhanceNano, No. 391979941), as well as the DFG-SNSF Joint Switzerland-German Research Project (EnhanTopo, No. 429265950). The authors acknowledge the use of computational facilities at the Center for information services and high performance computing (ZIH) at TU Dresden. Diffraction data have been collected on BL14.2 at the BESSY II electron storage ring operated by the Helmholtz-Zentrum Berlin, we thank Dr. Manfred Weiss and his team for assistance during the experiment.