Azatriseptanes: Strained Framework Analogs of [7,7,7]Circulenes

The syntheses and characterizations of heptagon-embedded polycyclic aromatic compounds are essential for understanding the effect of negative curvature on carbon allotropes such as fullerene and graphene that have applications in functional organic materials. However, owing to the synthetic difficulties in functionalizing and embedding 7-membered rings, these strain-challenged structures are relatively unexplored. We report here the synthesis and photophysical characterization of a triarylamine core bridged with ethane chains at the 2,2’-positions. In doing so, we provide access to the first heterocycle containing three fused heptagon rings with a nitrogen at its core (BATA-NHAc). DFT calculations and X-ray crystallography reveal a remarkably strained structure wherein two of the bridged aryl units approach coplanarity, whilst the third ring is twisted out of plane. The unique conformation of BATA-NHAc results in distinctive photophysical and electrochemical properties that open new avenues in understanding the structure-property relationships of curved π-aromatics and the construction of π-frameworks of increasing complexion.