Figure 2. Potential energy surfaces (PESs) as a function of intermolecular distance, R , (left) and rotational angle,θ , around the normal axis to the molecular plane of the carbazole at its center of mass (right) for the ground (S₀) and excited (T₁/S₁) states calculated with 6-311+G(d) basis set at SOS-MP2 and SOS-CIS(D₀) levels, respectively; in case of PES as a function of θ , the intermolecular distances correspond to the respective equilibrium distances. The calculated singlet and triplet vertical excitation energies of the carbazole at this level are ca. 4.23 and 3.69 eV, respectively.