A significant impact of nitrogen substitution on the solid state electronic structure: a case of 1,3,6,8-tetrakis(methylchalcogeno)-2,7-diazapyrene

Abstract

Nitrogen substitution of carbon atoms in polycyclic aromatic hydrocarbons is a promising approach to develop novel π-conjugated molecules, keeping a similar molecular shape and isoelectronic structure, both of which are key to maintaining a solid-state electronic structure that governs optoelectronic properties. We report here the synthesis and characterization of 1,3,6,8-tetrakis(methylthio)-2,7-diazapyrene (MT-azapyrene), together with its selenium analogue,1,3,6,8-tetrakis(methylseleno)-2,7-diazapyrene (MS-azapyrene), an isoelectronic homologue of the ultrahigh-mobility organic semiconductor, 1,3,6,8-tetrakis(methylthio)pyrene (MT-pyrene). For the synthesis of MT- and MS- azapyrene, we have newly developed 1,3,6,8-tetrachlcoro-2,7-diazapyrene, which was then utilized in nucleophilic aromatic substitution reaction with methilthiolate and methylselenolate anion. Single-crystal X-ray analysis revealed the molecular and crystal structures of MT- and MS-azapyrene; to our surprise, their crystal structures were characterized as one-dimensional inclined brickwork structures, markedly different from the two-dimensional brickwork structures of the pyrene counterparts, despite the similarity in molecular shape between the pyrene and azapyrene derivatives. Because of the difference in the crystal structures, the carrier mobility of MT- and MS-azapyrene was far lower, 0.073 cm² V^–1 s^–1 and 0.035 cm² V^–1 s^–1, respectively, than that of MT-pyrene (> 30 cm² V^–1 s^–1). These results demonstrate that even subtle structural changes, such as nitrogen substitution, alter the crystal structure and thus drastically alter transport properties.