Luminescent N-aryl-heteroacene derivatives

Abstract

The incorporation of heteroatoms into polycyclic aromatic hydrocarbons can alter their optical and electronic properties. Here, we report the synthesis and characterization of a series of N,N′-diaryl diazadioxatetrahydropentacenes (4a–e) as well as related N-phenyl azatrioxatetrahydropentacene and triazatetrahydrotetracene derivatives (5, 6) to investigate their photophysical properties and solid-state organization. These compounds were prepared from readily available compounds via a concise approach involving copper-catalyzed aryl amination, followed by nucleophilic aromatic substitution. The compounds display bright luminescence in solution and in the solid state and strong solvatochromism. Single-crystal X-ray diffraction of N,N′-aryl diazadioxatetrahydropentacenes (4b–d) revealed that all the compounds possessed nearly planar polycyclic aromatic systems with the pendant aryl groups nearly orthogonal to the pentacyclic core. Nonetheless, different substituents on the pendant aryl groups resulted in differences in photophysical properties because of differences in molecular geometries and solid-state packing. Interestingly, the N,N′-aryl diazadioxatetrahydropentacene bearing 2,6-dimethylphenyl groups attached to the nitrogen atoms (4d) gave two different polymorphs from the same solvent system, constituting a relatively rare example of concomitant polymorphism for such a rigid structure.