Fig. 2: TD-DFT evaluation of the potential energy landscape for rotation of phthalocyanines on NaCl.

a ZnPc⁺, b MgPc⁺ and c H₂Pc⁺ total energy (relative to the energy of the minima E_0min) as a function of rotation by angle ϕ for the ground and excited states. The computed energy is plotted with crosses and the corresponding parabolic fits around the local minima with solid lines. The insets show the schematic models of the respective ground state cations in their equilibrium positions. The angle ϕ is defined as between the molecule x-axes (crossing two opposing isoindole groups along N–N atom direction) and the nearest of the [110] and \([1\overline{1}0]\) NaCl crystallographic direction, as shown in the inset of a). d Detailed comparison of the potential well minima of the three cationic chromophores (computed as a difference with the energy of their respective minima E_0min or E_1min) as a function of the shift in the equilibrium angle positions Δϕ₀ between the ground and excited states. MgPc⁺ and H₂Pc⁺ ground and excited state are vertically offset by increments of 1 meV for clarity. Note the zero Δϕ₀ for H₂Pc⁺, imposed by the symmetry of the system. Source data are provided as a Source Data file.