Azaacenes are the analogue of acenes, comprising nitrogen atoms in the carbon-based molecular skeleton, have been gaining attention because of their potential application in organic electronics and material science. However, it is normally difficult to synthesize such large aromatic molecules because of the poor solubility and low stability. On the other hand, we have developed precursor methods to overcome these problems. Briefly, bicyclo[2.2.2]octadiene(BCOD)-fused acenes can be converted its corresponding acenes by thermally induced retro-Diels–Alder reaction, while α-diketone-type precursors can be converted simply by photoirradiation.[1] Significantly, these precursor molecules are often more soluble and stable than its converted forms. More crucially, their corresponding acenes can be prepared quantitatively in solutions or in films, if the precursors are sufficiently pure. So far, by using the precursor methods, we have successfully synthesized polyacenes under anaerobic conditions either at ultrahigh vacuum conditions or at the interior of single crystals to avoid undesirable oxidation of the resulting polyacenes.[2–4]

Here we report a series of tetraazapolyacene precursors synthesis. Briefly, the BCOD moieties were introduced in the tetraazaacenes as the thermally removable leaving group. The possibility of conversion of the precursors into its corresponding tetraazaacenes was examined by thermogravimetric analysis respectively. In addition, α-diketone-type precursor of tetraazaheptacene was also synthesized. Furthermore, we also report the one-pot synthesis of macrocyclic azacyclacene precursor by reacting bis-α-diketo-tetrahydro-diethanopentacene with benzene-1,2,4,5-tetraamine tetrahydrochloride. Here, the targeted compound was clearly confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The obtaining precursor compounds will be subjected to transformation to investigate its optical and physical properties.

References

1. H. Yamada, D. Kuzuhara, M. Suzuki, H. Hayashi, N. Aratani, Bull. Chem. Soc. Jpn. 2020, 93, 1234–1267.
2. J. I. Urgel, S. Mishra, H. Hayashi, J. Wilhelm, C. A. Pignedoli, M. D. Giovannantonio, R. Widmer, M. Yamashita, N. Hieda, P. Ruffieux, H. Yamada, F. Roman, Nat. Commun. 2019, 10, 861.
3. H. Hayashi, N. Hieda, M. Yamauchi, Y. S. Chan, N. Aratani, S. Masuo, H. Yamada, Chem. Eur. J. 2020, 26, 15079–15083.
4. K. Eimre, J. I. Urgel, H. Hayashi, M. D. Giovannantonio, P. Ruffieux, S. Sato, S. Otomo, Y. S. Chan, N. Aratani, D. Passerone, O. Gröning, H. Yamada, R. Fasel, C. A. Pignedoli, Nat. Commun. in press.