Synthesis of N+-Doped triphenylene derivatives by electrochemical intramolecular pyridination and their optoelectronic properties Yushi Ohno, Shogo Ando, Daisuke Furusho, Ryoyu Hifumi, Ikuyoshi Tomita, Shinsuke Inagi Tokyo Institute of Technology, Japan Polycyclic aromatic hydrocarbons (PAHs) have attracted attention for their unique properties due to their planar structure. Heteroatom-doping into the sp 2 -carbon frameworks of PAHs drastically alters their electronic structures and thus can easily modulate their optoelectronic properties. In particular, PAHs containing nitrogen cations (N + ) exhibit interesting optical properties and peculiar aggregation behavior based on the ionic moiety incorporated into π-systems. Therefore, N + -doped PAHs have led to their application in organic photocatalysts, ion-conductive materials, and bioimaging. However, the approaches to synthesize N + -doped PAHs are limited, [1] thus a facile synthesis is required to access N + -doped PAHs. In this study, we demonstrated the facile synthesis of N + -doped triphenylene derivatives by intramolecular cyclization via electro-oxidative S N Ar reaction. This protocol is a quite simple and efficient method without transition metal catalysts. First, the preparative-scale anodic oxidation of 1a was carried out under constant-current conditions in a divided cell equipped with a carbon felt anode, and a Pt plate cathode under the reported standard conditions for anodic pyridination of arenes [2] (Figure 1a). Under the optimized conditions, the intramolecular anodic pyridination successfully proceeded to yield product 2a in 60% isolated yield (84% NMR yield). Interestingly, the reactivity varied with the position of the methoxy groups. Furthermore, this reaction was tolerant to various aryl substitutions of the ortho -position of 2-phenylpyridine. (e.g., ethlenedioxy, dimethoxy, tolyl, phenyl, and naphthyl groups). However, 1f did not provide corresponding products 2f , but spiro compound 2f ’ (Figure 1b). The reactivity and regioselectivity of this reaction are consistent with the DFT simulation results for the β-LUMO coefficients 1a - 1j in their one-electron-oxidation state. As a result of the investigation of the optoelectronic properties, the obtained N + -doped triphenylene derivatives have high electron-accepting nature and good emission properties due to the incorporation of the pyridinium moiety. In single crystal X-ray diffraction analysis, N + -doped triphenylene derivatives formed relatively high planar structures except 2j , and columnar structures with cation species like charge-segregated assemblies with plane distances of 3.29 and 3.32 Å (Figure 1c). This result indicates that N + -doped triphenylene derivatives have the potential utility of organic semiconducting materials. In conclusion, we successfully achieved the facile synthesis of N + -doped triphenylene derivatives for the first time by intramolecular anodic pyridination. This method is very useful for introducing a nitrogen cation into PAHs to perturb the π-electron system.
References 1. a) N. Toriumi, N. Asano, K. Miyamoto, A. Muranaka, M. Uchiyama, J. Am. Chem. Soc . 2018 , 140 , 3858–3862; b) Y. Asanuma, H. Eguchi, H. Nishiyama, I. Tomita, S. Inagi, Org. Lett . 2017 , 19 , 1824–1827. 2. T. Morofuji, A. Shimizu, J. Yoshida, J. Am. Chem. Soc . 2013 , 135 , 5000–5003.
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