Synthesis and Photophysical Properties of Carbazole-Functionalized Diazaphosphepines via Sequent P-N Chemistry

Chemical structure tunability of organic π-conjugated molecules (OCMs) is highly appealing for fine-tuning the optoelectronic properties. Herein, we report a new series of carbazole-functionalized diazaphosphepines (DPP-CBZs) via one-pot phosphorus-nitrogen (P-N) chemistry. The one-pot synthesis harnessed the mild and selective P-N chemistry that successively installed carbazole moieties and seven-membered heterocycles at one P-center. Single-crystal structure studies revealed the tweezer-like structures for 1PO, 2PO, and 3PO that maintained the intramolecular donor-acceptor interactions between [d]-aryl moieties and carbazole. DPP-CBZs exhibited a more twisted central-diazaphosphepine ring compared with the reference molecules (1-3MO without carbazole group). DPP-CBZs with strong electron-accepting [d]-Ars generally showed lower photoluminescence quantum yields (PLQYs) than those of the reference molecules, which is probably due to the intramolecular charge transfer (ICT) from electron-donating carbazole to electron-withdrawing [d]-Ars. Upon the oxidation of the P-centers, PLQYs of DPP-CBZs increased. Furthermore, photophysical studies and theoretical studies suggested that the carbazole group had a strong impact on the structures of DPP-CBZs. As a proof of concept, we showed that grinding the mixture of 1PO as the electron-donating tweezer and benzene-1,2,4,5-tetracarbonitrile (BzCN) as the electron acceptor induced the formation of the CT complex.