Embedding seven-membered rings into polycyclic aromatic molecules is attractive as they can exert an influence on molecular conformation that ultimately changes the solubility and π-electronics. The considerations in designing and synthesizing a highly strained azatriseptane framework is discussed herein. We employ a twofold macrocyclization strategy to form the [7,7,7]-system and through scoping various strategies identify a Friedel-Crafts approach is key. The synthetic limitations we have identified, in addition to the successes presented here, highlights the key challenges in forming triseptane frameworks and paves the way for secondgeneration analogues that may have various applications in optical as well as electronic organic materials.

The synthesis and characterization of heptagonembedded polycyclic aromatic compounds are essential for understanding the effect of negative curvature on carbon allotropes such as fullerenes and graphenes that have applications in functional organic materials. However, owing to the synthetic difficulties in functionalizing and embedding seven-membered rings, these strain-challenged structures are relatively unexplored. We report here the synthesis, characterization, and properties of a triarylamine core bridged with ethano 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). X-ray crystallographic analysis and DFT calculations revealed a remarkably strained structure wherein two of the bridged aryl units approach coplanarity, while the third ring is twisted out of plane at 70°. UV-vis and emission spectroscopies identify red-shifted absorption and concentration-dependent emission profiles, respectively, as a result of the unique conformation and self-assembly properties of BATA-NHAc. Furthermore, cyclic voltammetry shows a decrease in the oxidation potential for BATA-NHAc in comparison to the non-bridged analog. This study opens new avenues in understanding the structure-property relationships of curved π-aromatics and the construction of π-frameworks of increasing complexity.

Invited for the cover of this issue is the group of Michel Rickhaus at the University of Zurich. The image depicts the “unearthing” of the highly contorted azatriseptane, a carbon framework consisting of three fused seven‐membered rings surrounding a central nitrogen. Read the full text of the article at 10.1002/chem.202203954.

Unearthing azatriseptane: Explore the properties and potential of a newly synthesized, highly strained carbon framework with a nitrogen core, containing three fused heptagon rings. This heterocycle could serve as an encouraging platform from which to explore the supramolecular behavior of these contorted hydrogen‐bonding systems or to obtain negatively curved nanographenes. More information can be found in the Research Article by M. Rickhaus and co‐workers (DOI: 10.1002/chem.202203954).

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.