Position Dependent Effects of the Aza‐Substitution on the Electronic Properties and Crystal Structures Based on Hexaazaphenalene Isomers

Abstract

We synthesized two hexaazaphenalene derivatives, 6AP-Pm (2, 5-di(tert-butyl)-1, 3, 4, 6, 7, 9b-hexaazaphenalene) and 6AP-Pz (2, 5-di(tert-butyl)-1, 3, 4, 6, 8, 9b-hexaazaphenalene) and compared the electronic properties with the pentaazaphenalene derivative 5AP (2, 5-di(tert-butyl)-1, 3, 4, 6, 9b-pentaazaphenalene). We clarified the position-dependent effects of the aza-substitution on the electronic states followed by the optical and electrochemical properties. In comparison to 5AP, 6AP-Pm had the blue-shifted UV-vis absorption spectrum due to the lowered HOMO level and the slightly affected LUMO level. On the other hand, 6AP-Pz showed the red-shifted UV-vis absorption spectrum owing to the slightly-affected HOMO level and the lowered LUMO level. From the theoretical investigations, it is suggested that one of frontier molecular orbitals can be lowered by the aza-substitution. Consequently, these opposite behaviors should be induced in the optical properties. Furthermore, 5AP, 6AP-Pm and 6AP-Pz showed the different favored packings in the crystalline state presumably because the effect on their dipole moments by the nitrogen atoms was varied. It is demonstrated that the aza-substitution to aromatic rings is applicable not only for specifically modulating the energy level of one of molecular orbitals but also for altering molecular distributions in crystal.