Distorted Nanographenes by Embedding a Cyclopenta[a]heptalene Core and Multiple Additional Heptagons: Chiral...

Nanographenes containing fused pentagon-heptagon units (e.g., 5-7, 5-7-5, or 7-5-7 ring motifs) have demonstrated remarkable electronic and photophysical properties, whereas carbon π-skeletons embedding well-defined 5-7-7 ring units remain elusive. Herein, we present two novel nanographenes incorporating a cyclopenta[a]heptalene core together with two (C70) or three (C88) additional heptagons, which were efficiently synthesized through Scholl reactions, providing four or five heptagons in one step. The embedded odd-membered rings impart favorable solubility, high photostability, multiple redox processes, and excellent fluorescence emission to π-systems. Single-crystal X-ray diffraction analyses revealed saddle-helix and saddle-twist hybrid conformations for C70 and C88, respectively. The smaller distorted saddle exists as a pair of enantiomers that are tightly interlocked into discrete π-dimers, while the larger twisted saddle of identical configuration self-assembled into banana-shaped columnar chiral π-dodecamers, in which six chlorobenzene molecules were alternately intercalated into the interlayers of 12 saddles, forming multilayer sandwich-like structures. Driven by a secondary nucleation event, these bent oligomeric stacks underwent hierarchical organization into quasi-hexagonal, offset-packed columnar arrays. Moreover, 1:1 cocrystallization of saddle C70 and fullerene C₆₀ in toluene afforded a C_i-symmetric 2:2:2 inclusion complex, which further self-assembled into multilayer supramolecular π-architectures. Our work demonstrates how larger distorted nanographenes with reduced symmetry, made accessible by integrating cyclopenta[a]heptalene core subunits and heptagons, can direct the formation of novel solid-state packing structures.