Planarization of negatively curved [7]circulene on a graphene monolayer

[7]Circulene (C₂₈H₁₄) is the smallest saddle-shaped [n]circulene with negative Gaussian curvature. The electronic properties of highly curved π-systems change upon planarization, and therefore the induced planarization of these systems has attracted considerable attention in recent years. Here we use dispersion-corrected density functional theory (DFT) calculations (at the PW6B95-D4/def2-QZVP level) to show that the highly nonplanar [7] circulene adopts a completely planar equilibrium structure upon adsorption on a nanographene (modeled as C₉₆H₂₄). This planarization is rooted in strong dispersion and electrostatic interactions between the [7]circulene and C₉₆H₂₄ (est. as △E_e,int = 166.9 kJ mol^{− 1} ), which are significantly stronger than the planarization energy of the free [7]circulene (est. as △E_e,planar = 40.0 kJ mol^{− 1} ). Upon planarization, the magnetic nature of [7]circulene changes from nonaromatic to antiaromatic. Thus, this graphene-induced planarization provides a novel approach for a reversible nonaromatic/antiaromatic molecular switch.