Synthesis, post-functionalization, and photoluminescence of contorted diazaphosphepine-based polycyclic aromatic heterocycles.

Heteroatom-doped organic π-conjugated molecules (OCMs) have become one type of emerging optoelectronic material with intriguing functionalities. Phosphorus (P)-doped OCMs are a special member of heteroatom-doped OCMs where rich P-chemistry is able to fine-tune their optoelectronic properties. Herein, we report a new series of nonplanar diazaphosphepine-based polycyclic aromatic heterocycles (DPP-PAHs). Efficient and mild double P-N cyclization allowed one to readily incorporate two P-centers in DPP-PAHs. With nonplanar diazaphosphepine rings, DPP-PAHs exhibit contorted structures in single crystal structures. The functionalization of double P-centers by HO and S gave DPP-PAHs with PO and PS centers, respectively. Compared with the parent small molecule, the DPP-PAHs exhibit high photoluminescence quantum yields. Our experimental and theoretical studies further revealed that both P-environments and conjugated backbones have impacts on the photophysical properties of the DPP-PAHs.