Central sp³-C Substitution Directs Supramolecular Assembly and Molecular Properties of Tris-HBC Nanographenes

Understanding how structural modifications control the electronic and supramolecular behavior of hexa-peri-hexabenzocoronene (HBC) nanographenes remains a central challenge in π-conjugated materials design. Here, we demonstrate that variation of a central sp³-C substituent in tris-HBC(tBu)₅ nanographenes modulates the electronic structure through combined through-bond and through-space effects. Single-crystal X-ray diffraction reveals a pronounced substituent-size dependence on supramolecular organization. The ─CH₃ derivative assembles exclusively via π-π stacking into well-separated two-dimensional parallel layers with one-dimensional channels. In contrast, the ─H analogue adopts offset antiparallel layered assemblies driven by cooperative π-π and C─H⋯arene edge contacts, bringing adjacent layers into closer proximity. Notably, solvent-mediated hydrogen-bonding induces a distinct layered arrangement in the ─OH analogue. The bulkier ─OCH₃ and ─OC₂H₅ substituents disrupt this packing motif, with only two HBC units participating in intermolecular π-π stacking, while the third engages in C─H⋯π interactions with a differently oriented neighboring unit, leading to a different packing arrangement. Consistent with these structural differences, systematic variations in redox potentials, photophysical responses, excited-state lifetimes, and vibrational features are observed, in good agreement with density functional theory (DFT) and time-dependent DFT calculations. Overall, central sp³ substitution provides an effective strategy for tuning structure-property relationships in tris-HBC nanographenes.