Dynamic Double Carbaporphyrin-Fused Nanographene: Facile Monolayer and Persistent Bilayer Switching

Manipulating the dynamic processes of nanographenes, from conformational flipping to supramolecular dimerization, is essential for gaining precise control over their properties and functions. In this study, a nanographene with two fused carbaporphyrin units (HBC2P) was synthesized by introducing dipyrromethene units into opposite bay areas of hexa-peri-hexabenzocoronene (HBC). HBC2P has a flexible monolithic skeleton, with a backbone length exceeding 1.8 nm. Its two conformations, referred to as "boat-shaped" and "chair-shaped," were individually achieved by selecting a suitable solvent. Notably, HBC2P forms a stable bilayer structure with two "boat-shaped" monomers arranged back-to-back in the polar solvents. Moreover, its flexible structure can be fixed by metal coordination, where the hollow ribbon-like nanographene is transformed into a planar metallized nanographene after the insertion of two Cu(III) ions. This metallization modulates the assembly behavior and terminates the dimerization behavior observed in the free-base form. This work provides a unique example of a nanographene that is fully tunable in its monomeric and dimeric forms, forms a stable bilayer in polar solvents, and has an assembly behavior that can be tuned further through metalation. The clarification of the structure-photophysical property relationships of such a dynamic nanographene offers guiding principles for the rational design of molecular bilayer graphenes and related π-conjugated systems with both tailored structures and tailored properties.