Singlet-triplet excitation energies of naphthyl cations: High level composite method calculations suggest a singlet ground state

► Singlet-triplet excitation energies (ES-T) calculated for phenyl, 1-naphthyl, and 2-naphthyl cations. ► Range of model chemistries and basis sets employed. ► Significant variability dependent on model chemistry. ► Composite methods indicate singlet ground state naphthyl cations. ► Magnitude of naphthyl cation ES-T sufficient that triplet state not appreciably populated.